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  • 1.
    Birznieks, Ingvars
    et al.
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Burstedt, Magnus K
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Edin, Benoni B
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Johansson, Roland S
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Mechanisms for force adjustments to unpredictable frictional changes at individual digits during two-fingered manipulation.1998In: Journal of Neurophysiology, ISSN 0022-3077, E-ISSN 1522-1598, Vol. 80, no 4, p. 1989-2002Article in journal (Refereed)
    Abstract [en]

    Previous studies on adaptation of fingertip forces to local friction at individual digit-object interfaces largely focused on static phases of manipulative tasks in which humans could rely on anticipatory control based on the friction in previous trials. Here we instead analyze mechanisms underlying this adaptation after unpredictable changes in local friction between consecutive trials. With the tips of the right index and middle fingers or the right and left index fingers, subjects restrained a manipulandum whose horizontal contact surfaces were located side by side. At unpredictable moments a tangential force was applied to the contact surfaces in the distal direction at 16 N/s to a plateau at 4 N. The subjects were free to use any combination of normal and tangential forces at the two fingers, but the sum of the tangential forces had to counterbalance the imposed load. The contact surface of the right index finger was fine-grained sandpaper, whereas that of the cooperating finger was changed between sandpaper and the more slippery rayon. The load increase automatically triggered normal force responses at both fingers. When a finger contacted rayon, subjects allowed slips to occur at this finger during the load force increase instead of elevating the normal force. These slips accounted for a partitioning of the load force between the digits that resulted in an adequate adjustment of the normal:tangential force ratios to the local friction at each digit. This mechanism required a fine control of the normal forces. Although the normal force at the more slippery surface had to be comparatively low to allow slippage, the normal forces applied by the nonslipping digit at the same time had to be high enough to prevent loss of the manipulandum. The frictional changes influenced the normal forces applied before the load ramp as well as the size of the triggered normal force responses similarly at both fingers, that is, with rayon at one contact surface the normal forces increased at both fingers. Thus to independently adapt fingertip forces to the local friction the normal forces were controlled at an interdigital level by using sensory information from both engaged digits. Furthermore, subjects used both short- and long-term anticipatory mechanisms in a manner consistent with the notion that the central nervous system (CNS) entertains internal models of relevant object and task properties during manipulation.

  • 2.
    Burstedt, Magnus K
    et al.
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Birznieks, Ingvars
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Edin, Benoni B
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Johansson, Roland S
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Control of forces applied by individual fingers engaged in restraint of an active object.1997In: Journal of Neurophysiology, ISSN 0022-3077, E-ISSN 1522-1598, Vol. 78, no 1, p. 117-128Article in journal (Refereed)
    Abstract [en]

    We investigated the coordination of fingertip forces in subjects who used the tips of two fingers to restrain an instrumented manipulandum with horizontally oriented grip surfaces. The grip surfaces were subjected to tangential pulling forces in the distal direction in relation to the fingers. The subjects used either the right index and middle fingers (unimanual grasp) or both index fingers (bimanual grasp) to restrain the manipulandum. To change the frictional condition at the digit-object interfaces, either both grip surfaces were covered with sandpaper or one was covered with sandpaper and the other with rayon. The forces applied normally and tangentially to the grip surfaces were measured separately at each plate along with the position of the plates. Subjects could have performed the present task successfully with many different force distributions between the digits. However, they partitioned the load in a manner that reflected the frictional condition at the local digit-object interfaces. When both digits contacted sandpaper, they typically partitioned the load symmetrically, but when one digit made contact with rayon and the other with sandpaper, the digit contacting the less slippery material (sandpaper) took up a larger part of the load. The normal forces were also influenced by the frictional condition, but they reflected the average friction at the two contact sites rather than the local friction. That is, when friction was low at one of the digit-object interfaces, only the applied normal forces increased at both digits. Thus sensory information related to the local frictional condition at the respective digit-object interfaces controlled the normal force at both digits. The normal:tangential force ratio at each digit appeared to be a controlled variable. It was adjusted independently at each digit to the minimum ratio required to prevent frictional slippage, keeping an adequate safety margin against slippage. This was accomplished by the scaling of the normal forces to the average friction and by partitioning of the load according to frictional differences between the digit-object interfaces. In conclusion, by adjusting the normal:tangential force ratios to the local frictional condition, subjects avoided excessive normal forces at the individual digit-object interfaces, and by partitioning the load according the frictional difference, subjects avoided high normal forces. Thus the local frictional condition at the separate digit-object interfaces is one factor that can strongly influence the distribution of forces across digits engaged in a manipulative act.

  • 3.
    Burstedt, Magnus K
    et al.
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Edin, Benoni B
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Johansson, Roland S
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Coordination of fingertip forces during human manipulation can emerge from independent neural networks controlling each engaged digit.1997In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 117, no 1, p. 67-79Article in journal (Refereed)
    Abstract [en]

    We investigated the coordination of fingertip forces in subjects who lifted an object (i) using the index finger and thumb of their right hand, (ii) using their left and right index fingers, and (iii) cooperatively with another subject using the right index finger. The forces applied normal and tangential to the two parallel grip surfaces of the test object and the vertical movement of the object were recorded. The friction between the object and the digits was varied independently at each surface between blocks of trials by changing the materials covering the grip surfaces. The object's weight and surface materials were held constant across consecutive trials. The performance was remarkably similar whether the task was shared by two subjects or carried out unimanually or bimanually by a single subject. The local friction was the main factor determining the normal:tangential force ratio employed at each digit-object interface. Irrespective of grasp configuration, the subjects adapted the force ratios to the local frictional conditions such that they maintained adequate safety margins against slips at each of the engaged digits during the various phases of the lifting task. Importantly, the observed force adjustments were not obligatory mechanical consequences of the task. In all three grasp configurations an incidental slip at one of the digits elicited a normal force increase at both engaged digits such that the normal:tangential force ratio was restored at the non-slipping digit and increased at the slipping digit. The initial development of the fingertip forces prior to object lift-off revealed that the subjects employed digit-specific anticipatory mechanisms using weight and frictional experiences in the previous trial. Because grasp stability was accomplished in a similar manner whether the task was carried out by one subject or cooperatively by two subjects, it was concluded that anticipatory adjustments of the fingertip forces can emerge from the action of anatomically independent neural networks controlling each engaged digit. In contrast, important aspects of the temporal coordination of the digits was organized by a "higher level" sensory-based control that influenced both digits. In lifts by single subjects this control was mast probably based on tactile and visual input and on communication between neural control mechanisms associated with each digit. In the two-subject grasp configuration this synchronization information was based on auditory and visual cues.

  • 4. Cipriani, Christian
    et al.
    Segil, Jacob L.
    Clemente, Francesco
    Weir, Richard F. Ff.
    Edin, Benoni
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Humans can integrate feedback of discrete events in their sensorimotor control of a robotic hand2014In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 232, no 11, p. 3421-3429Article in journal (Refereed)
    Abstract [en]

    Providing functionally effective sensory feedback to users of prosthetics is a largely unsolved challenge. Traditional solutions require high band-widths for providing feedback for the control of manipulation and yet have been largely unsuccessful. In this study, we have explored a strategy that relies on temporally discrete sensory feedback that is technically simple to provide. According to the Discrete Event-driven Sensory feedback Control (DESC) policy, motor tasks in humans are organized in phases delimited by means of sensory encoded discrete mechanical events. To explore the applicability of DESC for control, we designed a paradigm in which healthy humans operated an artificial robot hand to lift and replace an instrumented object, a task that can readily be learned and mastered under visual control. Assuming that the central nervous system of humans naturally organizes motor tasks based on a strategy akin to DESC, we delivered short-lasting vibrotactile feedback related to events that are known to forcefully affect progression of the grasp-lift-and-hold task. After training, we determined whether the artificial feedback had been integrated with the sensorimotor control by introducing short delays and we indeed observed that the participants significantly delayed subsequent phases of the task. This study thus gives support to the DESC policy hypothesis. Moreover, it demonstrates that humans can integrate temporally discrete sensory feedback while controlling an artificial hand and invites further studies in which inexpensive, noninvasive technology could be used in clever ways to provide physiologically appropriate sensory feedback in upper limb prosthetics with much lower band-width requirements than with traditional solutions.

  • 5. Clemente, Francesco
    et al.
    D'Alonzo, Marco
    Controzzi, Marco
    Edin, Benoni B.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Cipriani, Christian
    Non-Invasive, Temporally Discrete Feedback of Object Contact and Release Improves Grasp Control of Closed-Loop Myoelectric Transradial Prostheses2016In: IEEE transactions on neural systems and rehabilitation engineering, ISSN 1534-4320, E-ISSN 1558-0210, Vol. 24, no 12, p. 1314-1322Article in journal (Refereed)
    Abstract [en]

    Human grasping and manipulation control critically depends on tactile feedback. Without this feedback, the ability for fine control of a prosthesis is limited in upper limb amputees. Although various approaches have been investigated in the past, at present there is no commercially available device able to restore tactile feedback in upper limb amputees. Based on the Discrete Event-driven Sensory feedback Control (DESC) policy we present a device able to deliver short-lasting vibrotactile feedback to transradial amputees using commercially available myoelectric hands. The device (DESC-glove) comprises sensorized thimbles to be placed on the prosthesis digits, a battery-powered electronic board, and vibrating units embedded in an arm-cuff being transiently activated when the prosthesis makes and breaks contact with objects. The consequences of using the DESC-glove were evaluated in a longitudinal study. Five transradial amputees were equipped with the device for onemonth at home. Through a simple test proposed here for the first time-the virtual eggs test-we demonstrate the effectiveness of the device for prosthetic control in daily life conditions. In the future the device could be easily exploited as an add-on to complement myoelectric prostheses or even embedded in prosthetic sockets to enhance their control by upper limb amputees.

  • 6. Crea, Simona
    et al.
    Edin, Benoni B.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB).
    Knaepen, Kristel
    Meeusen, Romain
    Vitiello, Nicola
    Time-Discrete Vibrotactile Feedback Contributes to Improved Gait Symmetry in Patients With Lower Limb Amputations: Case Series2017In: Physical Therapy, ISSN 0031-9023, E-ISSN 1538-6724, Vol. 97, no 2, p. 198-207Article in journal (Refereed)
    Abstract [en]

    Background. Reduced sensory feedback from lower leg prostheses results in harmful gait patterns and entails a significant cognitive burden because users have to visually monitor their locomotion. Objectives. The purpose of this study was to validate a sensory feedback device designed to help elderly patients with transfemoral amputation to improve their temporal gait symmetry after a training program aimed at associating the vibrotactile patterns with symmetrical walking. Design. This was a prospective quasi-experimental study including 3 elderly patients walking with lower leg prostheses. Methods. During training sessions, participants walked on a treadmill equipped with feedback device that controlled vibrotactile stimulators based on signals from a sensorized insole while provided with visual feedback about temporal gait symmetry. The vibrotactile stimulators delivered short-lasting, low-intensity vibrations synchronously with certain gait phase transitions. During pretraining and posttraining sessions, participants walked without visual feedback about gait symmetry under 4 conditions: with or without vibrotactile feedback while performing or not performing a secondary cognitive task. The primary outcome measure was temporal gait symmetry. Results. with <= 52 hours of training,the participants improved their temporal gait symmetry from 0.82 to 0.84 during the pretraining evaluation session to 0.98 to 1.02 during the follow-up session across all conditions. Following training, participants were able to maintain good temporal gait synmsetry, without any evidence of an increased cognitive burden. Limitations. The small sample size and short follow-up time do not allow straightforward extrapolations to larger populations or extended time periods. Conclusions. Low-cost, gait phase-specific vibrotactile feedback after training combined with visual feedback may improve the temporal gait synmsetry in patients with transfemoral amputation without representing an additional cognitive burden.

  • 7. Delhaye, Benoit
    et al.
    Barrea, Allan
    Edin, Benoni B.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Lefèvre, Philippe
    Thonnard, Jean-Louis
    Surface strain measurements of fingertip skin under shearing2016In: Journal of the Royal Society Interface, ISSN 1742-5689, E-ISSN 1742-5662, Vol. 13, no 115, article id 20150874Article in journal (Refereed)
    Abstract [en]

    The temporal evolution of surface strain, resulting from a combination of normal and tangential loading forces on the fingerpad, was calculated from high-resolution images. A customized robotic device loaded the fingertip with varying normal force, tangential direction and tangential speed. We observed strain waves that propagated from the periphery to the centre of the contact area. Consequently, different regions of the contact area were subject to varying degrees of compression, stretch and shear. The spatial distribution of both the strains and the strain energy densities depended on the stimulus direction. Additionally, the strains varied with the normal force level and were substantial, e.g. peak strains of 50% with a normal force of 5 N, i.e. at force levels well within the range of common dexterous manipulation tasks. While these observations were consistent with some theoretical predictions from contact mechanics, we also observed substantial deviations as expected given the complex geometry and mechanics of fingertips. Specifically, from in-depth analyses, we conclude that some of these deviations depend on local fingerprint patterns. Our data provide useful information for models of tactile afferent responses and background for the design of novel haptic interfaces.

  • 8.
    Dimitriou, M
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB).
    Edin, Benoni B
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Discharges in Human Muscle Receptor Afferents during Block Grasping2008In: Journal of Neuroscience, ISSN 0270-6474, E-ISSN 1529-2401, Vol. 28, no 48, p. 12632-12642Article in journal (Refereed)
  • 9.
    Dimitriou, M
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB).
    Edin, Benoni B
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB).
    Discharges in human muscle spindle afferents during a key-pressing task2008In: The Journal of General Physiology, ISSN 0022-1295, E-ISSN 1540-7748, Vol. 586, no 22, p. 5455-5470Article in journal (Refereed)
  • 10.
    Dimitriou, M
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB).
    Edin, Benoni B
    Human muscle spindles act as forward sensory models.Manuscript (Other academic)
  • 11.
    Dimitriou, Michael
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Edin, Benoni B
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Human muscle spindles act as forward sensory models2010In: Current Biology, ISSN 0960-9822, E-ISSN 1879-0445, Vol. 20, no 19, p. 1763-1767Article in journal (Refereed)
    Abstract [en]

    Modern theories of motor control incorporate forward models that combine sensory information and motor commands to predict future sensory states. Such models circumvent unavoidable neural delays associated with on-line feedback control. Here we show that signals in human muscle spindle afferents during unconstrained wrist and finger movements predict future kinematic states of their parent muscle. Specifically, we show that the discharges of type Ia afferents are best correlated with the velocity of length changes in their parent muscles approximately 100-160 ms in the future and that their discharges vary depending on motor sequences in a way that cannot be explained by the state of their parent muscle alone. We therefore conclude that muscle spindles can act as "forward sensory models": they are affected both by the current state of their parent muscle and by efferent (fusimotor) control, and their discharges represent future kinematic states. If this conjecture is correct, then sensorimotor learning implies learning how to control not only the skeletal muscles but also the fusimotor system.

  • 12.
    Edin, Benoni
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Assigning biological functions: Making sense of causal chains2008In: Synthese, ISSN 0039-7857, E-ISSN 1573-0964, Vol. 161, no 2, p. 203-218Article in journal (Refereed)
  • 13.
    Edin, Benoni
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Quantitative analyses of dynamic strain sensitivity in human skin mechanoreceptors.2004In: Journal of Neurophysiology, ISSN 0022-3077, Vol. 92, no 6, p. 3233-43Article in journal (Refereed)
    Abstract [en]

    Microneurographical recordings from 24 slowly adapting (SA) and 16 fast adapting (FA) cutaneous mechanoreceptor afferents were obtained in the human radial nerve. Most of the afferents innervated the hairy skin on the back of the hand. The afferents' receptive fields were subjected to controlled strains in a ramp-and-hold fashion with strain velocities from 1 to 64%.s(-1), i.e., strain velocities within most of the physiological range. For all unit types, the mean variation in response onset approached 1 ms for strain velocities >8%.s(-1). Except at the highest strain velocities, the first spike in a typical SAIII unit was evoked at strains <0.5% and a typical SAII unit began to discharge at <1% skin strain. Skin strain velocity had a profound effect on the discharge rates of all classes of afferents. The "typical" peak discharge rate at the highest strain velocity studied was 50-95 imp/s(-1) depending on unit type. Excellent fits were obtained for both SA and FA units when their responses to ramp stretches were modeled by simple power functions (r2 > 0.9 for 95% of the units). SAIII units grouped with SAII with respect to onset latency and onset variation but with SAI units with respect to dynamic strain sensitivity. Because both SA and FA skin afferents respond strongly, quickly, and accurately to skin strain changes, they all seem to be able to provide useful information about movement-related skin strain changes and therefore contribute to proprioception and kinesthesia.

  • 14.
    Edin, Benoni B.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Classification of muscle stretch receptor afferents in humans1988Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The response patterns of human stretch receptors in the finger extensor muscles of the forearm were studied using the microneurography technique. Single-unit recordings were obtained from one-hundred and twenty-four afferents. A procedure was developed to classify the units in muscle spindle primary afferents, secondary afferents, and Golgi tendong organ afferents. The procedure allows an objective and reproducible classification on the basis of the afferents’ responses to a series of tests which individually are non-conclusive.

    It was demonstrated that maximal twitch contractions can be elicited in the finger extensor muscles of the forearm, without causing undue discomfort to the subjects, or hazarding the single-unit recording. The response of the units to this test allowed, in most cases but not always, a separation in muscle spindle and tendon organ afferents. Thus the test was not adequate for an unequivocal classification.

    Three discrete response parameters were extracted from ramp-and-hold stretches, viz. the presence or absence of an initial burst and a deceleration response, and prompt silencing at slow muscle shortening. The distributions of the parameters were significantly different among the three unit types. These parameters which were pair-wise independent constituted a set of considerable discriminative power. It was shown that human muscle spindles have about the same static position sensitivity to fractional muscle stretch as previously found in animals.

    Stretch sensitization was demonstrated by rapid, repeated stretches of the muscle which enhanced the réponse to subsequent slow stretches of muscle spindles. Sensitization was different with primary and secondary muscle spindle afferents whereas Golgi tendon organ afferents never displayed stretch sensitization.

    One-to-one driving with small-amplitude sinusoidal stretches superimposed on ramp-and- hold stretches was almost exclusively seen with primary muscle spindle afferents, whereas secondaries seldom and tendon organ afferents never displayed driving.

    The afferent responses during slowly increasing isometric contractions and rapid relaxations were analysed. An increased discharge rate on relaxation was common among spindle afferents whereas it was never seen in tendon organs afferents. Two separate groups of spindles afferents were found with regard to fusimotor recruitment. The largest group was recruited at rather low and variable contractile forces whereas the smaller group was not recruited at all.

    The proportions of the three unit types, spindle primary, spindle secondary, and Golgi tendon organ afferents were estimated from a preliminary classification and the distribution of the eight response features were analyzed for each class of afferents. On the basis of these estimates and the response pattern of the individual unit Bayes’ theorem was used to calculate the probabilities that the unit was a spindle primary, a spindle secondary, or a tendon organ afferent. Estimates indicate that about 19 out of 20 muscle afferents are correctly classified when all eight features are analyzed.

  • 15.
    Edin, Benoni B
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Cutaneous afferents provide information about knee joint movements in humans.2001In: Journal of Physiology, ISSN 0022-3751, E-ISSN 1469-7793, Vol. 531, no Pt 1, p. 289-297Article in journal (Refereed)
    Abstract [en]

    1. Neurophysiological evidence that afferent information from skin receptors is important for proprioception has been gathered mainly in experiments relating to the human hand and finger joints. To investigate if proprioceptive information is also provided by skin mechanoreceptor afferents from skin areas related to large joints of postural importance, microneurography recordings were obtained in humans from skin afferents in the lateral cutaneous femoral nerve to study their responses to knee joint movements. 2. Data were collected from 60 sequentially recorded afferents from slowly (n = 23) and fast (n = 6) adapting low-threshold mechanoreceptors, hair follicle receptors (n = 24), field receptors (n = 1) and C mechanoreceptors (n = 6). Fascicular recordings showed that the lateral cutaneous femoral nerve supplies extensive areas of the thigh: from 5-10 cm below the inguinal ligament down to below and lateral to the knee joint; accordingly, the afferents originated in receptors located in wide areas of the human thigh. 3. All afferents from fast and slowly adapting low-threshold mechanoreceptors, as well as C mechanoreceptors, responded to manually applied skin stretch. In contrast, the same stimulus elicited, at most, feeble responses in hair follicle receptors. 4. Qualitative and quantitative analyses of the responses of a subset of afferents revealed that in particular slowly adapting afferents effectively encode both static and dynamic aspects of passively imposed knee joint movements. 5. It was concluded that receptors in the hairy skin of humans can provide high-fidelity information about knee joint movements. A previously undefined type of slowly adapting receptor (SA III) seemed particularly suited for this task whereas this does not seem to be the case for either hair follicle receptors or C mechanoreceptors.

  • 16.
    Edin, Benoni B
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Finger joint movement sensitivity of non-cutaneous mechanoreceptor afferents in the human radial nerve.1990In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 82, no 2, p. 417-422Article in journal (Refereed)
    Abstract [en]

    The responses of non-cutaneous receptors in the human hand to normal digit movements were studied using single afferent recordings from the radial nerve. Eight joint-related afferents had thresholds of 50 mN or less. All responded to passive flexion movements within the physiological range of joint rotation and showed predominantly static response sensitivity; none increased its discharge during passive extension. However, only two of these eight afferents showed the same response pattern during active movements; three discharged only during the extension phase whereas the other three discharged both during extension and flexion. No high-threshold, joint-related mechanoreceptive afferents were encountered in a population of 148 afferents recorded from the cutaneous portion of the radial nerve indicating a scarcity of such afferents on the dorsal aspect of finger joints. Seven high-threshold, subcutaneous mechanoreceptive units not related to joints had thresholds for indentations of 50 mN or more and lacked responses to finger movements. Low-threshold mechanoreceptive afferents related to joints in the human hand may thus provide kinematic information in the physiological mid-range of both passive and active movements. Joint position cannot, however, be derived unambiguously from their discharge since the receptor responses may be dramatically altered by muscle activity.

  • 17.
    Edin, Benoni B
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Quantitative analysis of static strain sensitivity in human mechanoreceptors from hairy skin.1992In: Journal of Neurophysiology, ISSN 0022-3077, E-ISSN 1522-1598, Vol. 67, no 5, p. 1105-1113Article in journal (Refereed)
    Abstract [en]

    1. Microelectrode recordings from 15 slowly adapting (SA) cutaneous mechanoreceptor afferents originating in hairy skin were obtained from the radial nerve in humans. 2. Controlled skin stretch was applied to the back of the hand that encompassed the physiological range of skin stretch during movements at the metacarpophalangeal (MCP) joints. 3. Both SA Group I and II afferents showed exquisite dynamic and static sensitivity to skin stretch. The median static strain sensitivity was 1.0 imp.s-1 per percent skin stretch for SAI units and 1.8 for SAII units. 4. Translated into sensitivity to movements at the MCP joint, both SAI and SAII afferents in the skin of the back of the hand displayed a positional sensitivity that was comparable with that reported for muscle spindle afferents. 5. These data give quantitative support to suggestions that skin receptors in the human hairy skin provide information on nearby joint configurations and therefore may play a specific role in proprioception, kinesthesia, and motor control.

  • 18.
    Edin, Benoni B
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    The 'initial burst' of human primary muscle spindle afferents has at least two components.1991In: Acta Physiologica Scandinavica, ISSN 0001-6772, E-ISSN 1365-201X, Vol. 143, no 2, p. 169-175Article in journal (Refereed)
    Abstract [en]

    Ten muscle spindle primary afferents from the extensor digitorum communis muscle of man were studied with single unit afferent recordings. Responses to slow test stretches with three different pre-history conditions were assessed to investigate the contribution of rapid stretches to the stretch sensitization phenomenon. In two of the conditions, the slow test ramps were preceded by rapid stretch after which the parent muscle of the receptor was either (a) kept short for 5 seconds or (b) kept long for 3.2 seconds and then returned to the short muscle length for 5 seconds. The third condition (c) consisted of a slow stretch from short to long muscle length followed by a rapid return to the short muscle length, in turn followed by 5 seconds at the short muscle length. Afferent responses were depressed when the muscle had been kept at the long length after the rapid stretches (condition b) and enhanced when the muscle had been kept at the short length (conditions a & c). A prominent 'initial burst' was only present in the afferent discharge when the parent muscles of the primary endings had been kept short (condition a). A second, more prolonged burst was present for conditions (a) and (c) but was lacking or inconspicuous when the muscle had been kept long after rapid stretches (condition b). The rapid stretches in the stretch sensitization paradigm appear to be a primary factor not only for the enhanced responses of sensitized primary afferents but also for the depressed responses of desensitized primary afferents.

  • 19.
    Edin, Benoni B
    et al.
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Abbs, J H
    Finger movement responses of cutaneous mechanoreceptors in the dorsal skin of the human hand.1991In: Journal of Neurophysiology, ISSN 0022-3077, E-ISSN 1522-1598, Vol. 65, no 3, p. 657-670Article in journal (Refereed)
    Abstract [en]

    1. The movement sensitivity of dorsal skin mechanoreceptors in the human hand was studied by the use of single afferent recording techniques. 2. Units were classified as slowly (SA) and fast adapting (FA) and further characterized by thresholds to vertical indentation and by receptive-field sizes. Whereas SA units were evenly distributed within the supply area of the superficial branch of the radial nerve. FA units were usually situated near joints. 3. The proportion of different receptor types (32% SAI, 32% SAII, 28% FAI, 8% FAII; n = 107) compared favorably with previous electrophysiological and anatomic data, arguing for minimal sampling bias. The majority of the skin mechanoreceptive units were SA, largely due to a relative scarcity of FAII [Pacinian corpuscles (PC)] units. 4. A large majority (92%) of the afferents responded to active hand or finger movements. Responses in all unit types were consistent with observed movement-induced deformations of their receptive fields. 5. FAI units responded bidirectionally, albeit usually with somewhat higher discharge frequencies for finger flexion, which in most cases were associated with skin stretch. FAI units showed meager responses to remote stimuli, typically responding to one or, at the most, two adjacent joints. 6. SA units typically showed simple directional responses to joint movements with an increased discharge during flexion and a reduced discharge during extension. Joint movement that influenced the skin within the receptive field of SA units elicited graded responses even if the field, as assessed by perpendicular indentations, was minute. This finding suggests that definition of cutaneous receptive fields by classical perpendicular indentations may be inappropriate for the receptors in the hairy, nonglabrous skin. 7. The interpretation of the data from these recordings suggests that cutaneous mechanoreceptors in the dorsal skin can provide the CNS with detailed kinematic information, at least for movements of the hand.

  • 20.
    Edin, Benoni B
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Ascari, L
    Beccai, L
    Roccella, S
    Cabibihan, J-J
    Carrozza, M C
    Bio-inspired sensorization of a biomechatronic robot hand for the grasp-and-lift task.2008In: Brain Research Bulletin, ISSN 0361-9230, E-ISSN 1873-2747, Vol. 75, no 6, p. 785-95Article in journal (Refereed)
    Abstract [en]

    It has been concluded from numerous neurophysiological studies that humans rely on detecting discrete mechanical events that occur when grasping, lifting and replacing an object, i.e., during a prototypical manipulation task. Such events represent transitions between phases of the evolving manipulation task such as object contact, lift-off, etc., and appear to provide critical information required for the sequential control of the task as well as for corrections and parameterization of the task. We have sensorized a biomechatronic anthropomorphic hand with the goal to detect such mechanical transients. The developed sensors were designed to specifically provide the information about task-relevant discrete events rather than to mimic their biological counterparts. To accomplish this we have developed (1) a contact sensor that can be applied to the surface of the robotic fingers and that show a sensitivity to indentation and a spatial resolution comparable to that of the human glabrous skin, and (2) a sensitive low-noise three-axial force sensor that was embedded in the robotic fingertips and showed a frequency response covering the range observed in biological tactile sensors. We describe the design and fabrication of these sensors, their sensory properties and show representative recordings from the sensors during grasp-and-lift tasks. We show how the combined use of the two sensors is able to provide information about crucial mechanical events during such tasks. We discuss the importance of the sensorized hand as a test bed for low-level grasp controllers and for the development of functional sensory feedback from prosthetic devices.

  • 21.
    Edin, Benoni B
    et al.
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Bäckström, P A
    Bäckström, L O
    Single unit retrieval in microneurography: a microprocessor-based device controlled by an operator.1988In: Journal of Neuroscience Methods, ISSN 0165-0270, E-ISSN 1872-678X, Vol. 24, no 2, p. 137-144Article in journal (Refereed)
    Abstract [en]

    A microprocessor-based device was constructed to retrieve single unit activity from nerve recordings contaminated by other units and EMG activity. The microneurographic signal is sampled at 10 kHz and an algorithm applied to identify impulses from a single nerve fibre. On line, a TTL pulse is delivered when an event, i.e. a provisional nerve impulse, is selected. The wave form and clock time of events are stored. Moreover, the latest selected event and the actual selection criteria are continuously displayed on a standard oscilloscope. Off line, the wave form and clock time of events as well as an instantaneous frequency plot can be displayed on the oscilloscope. The final selection of events is done with a combination of a second algorithm, which essentially is a wave form comparator, and a manual check. The device is controlled either by hardware, with knobs on the front panel, or by software through a data bus connected to a microcomputer. Clock times and wave forms of the events, which are stored in the microprocessor memory, may also be presented on the data bus for later off-line analysis and coordination with other related signals collected during the experiment, e.g. transducer and electromyography records, whether these were stored on analog or digital tape or computer disc. Compared to other available techniques, the device has a superior discriminative power when electromyographic artefacts are present.

  • 22.
    Edin, Benoni B
    et al.
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Essick, G K
    Trulsson, Mats
    Olsson, Kurt Å
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Receptor encoding of moving tactile stimuli in humans. I. Temporal pattern of discharge of individual low-threshold mechanoreceptors.1995In: Journal of Neuroscience, ISSN 0270-6474, E-ISSN 1529-2401, Vol. 15, no 1 Pt 2, p. 830-847Article in journal (Refereed)
    Abstract [en]

    The response of 70 cutaneous, low-threshold mechanoreceptors in the human median, radial and inferior alveolar nerves to well controlled brush stimuli moving across the receptive field was quantitatively studied. Microneurography was used to obtain the response of each to multiple velocities from 0.5 to 32 cm/sec in at least two opposing directions. A high degree of response consistency was observed from the slowly adapting receptors to replication of the same stimulus and to a lesser, but significant degree from the fast adapting receptors. The evoked discharge reflected up to three partially overlapping phases of the moving stimulus: skin compression, indentation, and stretch. Although the overall discharge rate increased with both stimulus velocity and force, the spatial discharge pattern was preserved to a high degrees. In contrast, the discharge patterns differed for opposing and orthogonal directions. Reducing the area of skin surrounding the receptive field that was contacted by the moving stimuli had little effect on the evoked response. Individual mechanoreceptors display highly reliable differences to brush stimuli moving at different velocities. to brush stimuli moving at different velocities. Moreover, different directions of movement evoke differences in the discharge that are consistently observed upon replication of the same stimuli. Despite the richness and consistency in the spatial discharge pattern displayed by individual receptors, it is argued that the details of the patterns are not likely used by the CNS to infer information about direction and velocity of movement across the skin. Rather, the intensity of discharge is proposed as a plausible information-bearing attribute of the stimulus-evoked response.

  • 23.
    Edin, Benoni B
    et al.
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Howe, Robert
    Westling, Göran
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Cutkosky, Mark
    A Physiological Method for Relaying Frictional Information to a Human Teleoperator1993In: IEEE Transactions on Systems, Man and Cybernetics, ISSN 0018-9472, E-ISSN 2168-2909, Vol. 23, no 2, p. 427-432Article in journal (Refereed)
    Abstract [en]

    The ability to sense and respond to frictional variations is important for dexterous manipulation. It has been demonstrated that humans apply forces to an object on the basis of its anticipated frictional properties. After contact , tactile receptors provide information on the actual frictional properties and ensure that the applied finger tip allow for a safety margin against slips during the ensuing manipulation. With inappropriate forces, incipient and overt slips occur which produce receptor discharges and elicit automatic adjustments of the finger tip forces to increase the safety margins against future slips. It is demonstrated that it is possible to elicit rapid, nonhabituating and sustained grasp responses by means of a tactile display. Subjects grasped and lifted an instrumented test object using the thumb and index finger. While the object was held in air, rapid but small sliding movements were invoked between the object and either contact plate and caused a load force redistribution. This reliably triggered a grasp force increase similar to the ones elicited by natural slips occuring during normal manipulation. An important application of this finding is in relaying frictional information from a slave hand to a human operator. Furthermore, it may make it possible to reduce disparity between master and slave hands in force reflective telemanipulation systems.

  • 24.
    Edin, Benoni B
    et al.
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Johansson, Niclas
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Skin strain patterns provide kinaesthetic information to the human central nervous system.1995In: Journal of Physiology, ISSN 0022-3751, E-ISSN 1469-7793, Vol. 487, no 1, p. 243-251Article in journal (Refereed)
    Abstract [en]

    1. We investigated the contribution of skin strain-related sensory inputs to movement perception and execution in five normal volunteers. The dorsal and palmar skin of the middle phalanx and the proximal interphalangeal (PIP) joint were manipulated to generate specific strain patterns in the proximal part of the index finger. To mask sensations directly related to this manipulation, skin and deeper tissues were blocked distal to the mid-portion of the proximal phalanx of the index finger by local anaesthesia. 2. Subjects were asked to move their normal right index finger either to mimic any perceived movements of the anaesthetized finger or to touch the tip of the insentient finger. 3. All subjects readily reproduced actual movements induced by the experimenter at the anaesthetized PIP joint. However, all subjects also generated flexion movements when the experimenter did not induce actual movement but produced deformations in the sentient proximal skin that were similar to those observed during actual PIP joint flexion. Likewise, the subjects indicated extension movement at the PIP joint when strain patterns corresponding to extension movements were induced. 4. In contrast, when the skin strain in the proximal part of the index finger was damped by a ring applied just proximal to the PIP joint within the anaesthetized skin area, both tested subjects failed to perceive PIP movements that actually took place.(ABSTRACT TRUNCATED AT 250 WORDS)

  • 25.
    Edin, Benoni B
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Trulsson, Mats
    Neural network analysis of the information content in population responses from human periodontal receptors1992In: Proceedings of SPIE, the International Society for Optical Engineering, ISSN 0277-786X, E-ISSN 1996-756X, Vol. 1710, p. 257-266Article in journal (Refereed)
    Abstract [en]

    Understanding of the information processing in some sensory systems is hampered for several reasons. First, some of these systems may depend on several receptor types with different characteristics, and the crucial features of natural stimuli encoded by the receptors are rarely known with certainty. Second, the functional output of sensory processing is often not well defined. The human tooth is endowed with several types of sensory receptors. Among these, the mechanoreceptors located in the periodontal ligaments have been implicated in force encoding during chewing and biting. Individual receptors cannot, however, code unambiguously either the direction or the magnitude of the applied forces. Neuronal responses recorded in single human nerve fibers from periodontal receptors were fed to multi-layered feed-forward networks. The networks were trained with error back-propagation to identify specific features of the force stimuli that evoked the receptor responses. It was demonstrated that population responses in periodontal receptors contain information about both the point of attack and the direction of applied forces. It is concluded that networks may provide a powerful tool to investigate the information content in responses from biological receptor populations. As such, specific hypotheses with respect to information processing may be tested using neural networks also in sensory systems less well understood than, for instance, the visual system.

  • 26.
    Edin, Benoni B
    et al.
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Vallbo, A B
    Classification of human muscle stretch receptor afferents: a Bayesian approach.1990In: Journal of Neurophysiology, ISSN 0022-3077, E-ISSN 1522-1598, Vol. 63, no 6, p. 1314-1322Article in journal (Refereed)
    Abstract [en]

    1. A sample of 124 human muscle afferents originating from the finger extensor muscles were recorded from the radial nerve in the upper arm. A method is described to formalize the classification of units in muscle spindle primary and secondary afferents and Golgi tendon organ afferents on the basis of a few, nonrigorous assumptions. The classification was based on experimental data that largely have been described in a series of previous papers, although some additional data were collected in the present study. 2. The units were subjected to five tests providing identification data: twitch contraction test, ramp-and-hold stretch, small-amplitude sinusoidal stretches superimposed on ramp stretch, stretch sensitization, and isometric contraction/relaxation. From these five tests the following eight response features were extracted: response to maximal isometric twitch contractions, type of stretch sensitization, correlation between discharge rate and contractile force, response to sudden isometric relaxation, presence or absence of an initial burst, deceleration response, prompt silencing at slow muscle shortening, and driving by small-amplitude sinusoidal stretches. 3. A Bayesian decision procedure was adopted to classify the units on the basis of the eight discriminators. As a first step, units were provisionally classified into muscle spindle primary and secondary afferents, and Golgi tendon organ afferents, by intuitively weighting their responses to the identification tests. Prior probabilities were estimated on the basis of the provisional classification. The eight response features were analyzed and tabulated for all afferents, and the likelihood functions of the tests were directly calculated on the basis of these data.(ABSTRACT TRUNCATED AT 250 WORDS)

  • 27.
    Edin, Benoni B
    et al.
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Vallbo, A B
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Dynamic response of human muscle spindle afferents to stretch.1990In: Journal of Neurophysiology, ISSN 0022-3077, E-ISSN 1522-1598, Vol. 63, no 6, p. 1297-1306Article in journal (Refereed)
    Abstract [en]

    1. One hundred and twenty-four muscle afferents from the finger extensor muscles were recorded from the radial nerve in human subjects. 2. The afferents were provisionally classified as muscle spindle primary (78/124) and secondary afferents (25/124), and Golgi tendon organ afferents (21/124), on the basis of their response to 1) maximal twitch contractions, 2) 20- and 50-Hz sinusoids superimposed on ramp-and-hold stretches, 3) stretch sensitization, and 4) isometric contractions and sudden relaxations. 3. Ramp-and-hold stretches at two velocities, 10 and 50 degrees/s, were applied to the appropriate metacarpophalangeal (MCP) joint while the parent muscle remained relaxed. For each unit three discrete parameters were assessed: the presence or absence of 1) an initial burst at the commencement of the ramp stretch, 2) a deceleration response at the beginning of the hold phase, and 3) a prompt silencing at muscle shortening. In addition, two kinds of dynamic indexes were calculated for 79 of the muscle spindle afferents. 4. Most spindle afferents responded readily to stretch, whereas the Golgi tendon organ afferents produced very poor stretch responses. All of them lacked a static response, whereas the dynamic response, when present at all, consisted of only a few impulses. 5. The dynamic index was higher for spindle primaries than for secondaries, and this difference was statistically significant although the distribution was unimodal for spindle afferents as a group. Hence, this parameter was a poor discriminator. 6. Initial bursts, deceleration responses, and silences during imposed shortening were more common in spindle primaries than in secondaries. The differences were significant in all these respects. 7. The three discrete parameters were statistically pairwise independent for the spindle afferents, justifying the combination of the three into a useful battery for discrimination between primary and secondary spindle afferents and the use of this battery as a partial data base for a probability approach towards a solid classification of human muscle afferents.

  • 28.
    Edin, Benoni B
    et al.
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Vallbo, A B
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Muscle afferent responses to isometric contractions and relaxations in humans.1990In: Journal of Neurophysiology, ISSN 0022-3077, E-ISSN 1522-1598, Vol. 63, no 6, p. 1307-1313Article in journal (Refereed)
    Abstract [en]

    1. One hundred and two single afferents from the finger extensor muscles of humans were studied with the microneurography technique. 2. The afferents were provisionally classified as primary muscle spindle afferents (62/102), secondary spindle afferents (22), and Golgi tendon organ afferents (18) on the basis of their responses to four tests: 1) ramp-and-hold stretch, 2) 20- and 50-Hz small-amplitude sinusoidal stretch superimposed on ramp-and-hold stretch, 3) maximal isometric twitch contraction, and 4) stretch sensitization. 3. The response profiles of the three unit types were analyzed during slowly rising isometric contraction terminating with an abrupt relaxation. About 75% (61/84) of all muscle spindle afferents increased their discharge during isometric contraction, whereas the discharge was reduced for the remaining afferents. All Golgi tendon organs increased their discharge during the contraction. 4. The level of extrafusal contraction at which a spindle afferent increased its discharge rate often varied from trial to trial, speaking against a fixed fusimotor recruitment level of the individual spindle ending. 5. In 70% of the spindle afferents, a distinct burst of impulses appeared when the subject rapidly relaxed after the isometric contraction. The burst was more common and usually much more prominent with primary than secondary afferents, often reaching instantaneous discharge rates well above 100 Hz. 6. Whereas all Golgi tendon organ afferents displayed an increased discharge during the contraction phase, only one of them exhibited a rate acceleration close to the relaxation phase. However, this response could clearly be identified as being of different nature than the spindle bursts.(ABSTRACT TRUNCATED AT 250 WORDS)

  • 29.
    Edin, Benoni B
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Vallbo, A B
    Stretch sensitization of human muscle spindles.1988In: Journal of Physiology, ISSN 0022-3751, E-ISSN 1469-7793, Vol. 400, p. 101-11Article in journal (Refereed)
    Abstract [en]

    1. Sixty-seven afferents from the finger extensor muscles were consecutively recorded by microneurography. 2. The units were classified as primary or secondary muscle spindle afferents or Golgi tendon organ afferents on the basis of their responses to ramp-and-hold stretches, sinusoidals superimposed on ramp-and-hold stretches, maximal twitch contractions and isometric contractions and relaxations. 3. The muscle was repeatedly stretched and then either kept short or long for a few seconds followed by a slow ramp stretch. The responses of the muscle afferents to the slow stretch were compared under the two conditions. 4. Thirty out of thirty-eight units classified as primary spindle afferents and four out of eleven units classified as secondary afferents showed an enhanced response to the slow ramp when the muscle had been kept short compared to the response when the muscle had been kept long. 5. None of the eighteen Golgi tendon organ afferents showed any difference in this respect. 6. It is concluded that stretch sensitization does occur in human muscle spindles and, when present, constitutes firm evidence of the afferent originating from a muscle spindle rather than a Golgi tendon organ. In addition, due to differences in the response characteristics of primaries and secondaries, the test may aid in separating muscle spindle primary afferents from secondary afferents.

  • 30.
    Edin, Benoni B
    et al.
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Vallbo, A B
    Twitch contraction for identification of human muscle afferents.1987In: Acta Physiologica Scandinavica, ISSN 0001-6772, E-ISSN 1365-201X, Vol. 131, no 1, p. 129-138Article in journal (Refereed)
    Abstract [en]

    A classical test to differentiate between Golgi tendon organs and muscle spindles is the twitch contraction elicited by electrical stimulation. The possibility of producing maximal twitches in the finger extensor muscles using surface stimulation over the muscle belly was investigated as well as the feasibility of the test in microneurography experiments. Electrical stimuli were applied either over the muscle in the forearm or the radial nerve in the upper arm, while the resulting torque output at single metacarpophalangeal joints was measured. The relationship between current intensity and maximal contraction force was determined and stimulus response plots were constructed over a large range of current intensities. Stimulation of the radial nerve always yielded plots with a steep and monotonous rising limb up to a plateau. It was concluded that the plateau represented maximal twitch contractions. With transcutaneous stimulation over the muscle belly, the stimulus response plots were usually more complex. However, this could be explained by force transmission through the intertendinous connections on the dorsum of the hand and by antagonist activation. It was concluded that maximal twitch contractions can readily be elicited in the human extensor digitorum muscle with nonpainful transcutaneous electrical stimulations. Moreover, maximal twitches are compatible with single unit recording from muscle afferents in microneurography experiments.

  • 31.
    Edin, Benoni B
    et al.
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Westling, Göran
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Johansson, Roland S
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Independent control of human finger-tip forces at individual digits during precision lifting.1992In: Journal of Physiology, ISSN 0022-3751, E-ISSN 1469-7793, Vol. 450, p. 547-64Article in journal (Refereed)
    Abstract [en]

    1. Subjects lifted an object with two parallel vertical grip surfaces and a low centre of gravity using the precision grip between the tips of the thumb and index finger. The friction between the object and the digits was varied independently at each digit by changing the contact surfaces between lifts. 2. With equal frictional conditions at the two grip surfaces, the finger-tip forces were about equal at the two digits, i.e. similar vertical lifting forces and grip forces were used. With different frictions, the digit touching the most slippery surface exerted less vertical lifting force than the digit in contact with the rougher surface. Thus, the safety margins against slips were similar at the two digits whether they made contact with surfaces of similar or different friction. 3. During digital nerve block, large and variable safety margins were employed, i.e. the finger-tip forces did not reflect the surface conditions. Slips occurred more frequently than under normal conditions (14% of all trials with nerve block, <5% during normal conditions), and they only occasionally elicited compensatory adjustments of the finger-tip forces and then at prolonged latencies. 4. The partitioning of the vertical lifting force between the digits was thus dependent on digital afferent inputs and resulted from active automatic regulation and not just from the mechanics of the task. 5. The safety margin employed at a particular digit was mainly determined by the frictional conditions encountered by the digit, and to a lesser degree by the surface condition at the same digit in the previous lift (anticipatory control), but was barely influenced by the surface condition at the other digit. 6. It was concluded that the finger-tip forces were independently controlled for each digit according to a 'non-slip strategy'. The findings suggest that the force distribution among the digits represents a digit-specific lower-level neural control establishing a stable grasp. This control relies on digit-specific afferent inputs and somatosensory memory information. It is apparently subordinated to a higher-level control that is related to the total vertical lifting and normal forces required by the lifting task and the relevant physical properties of the manipulated object.

  • 32.
    Edin, Benoni
    et al.
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Beccai, L
    Ascari, L
    Roccella, S
    Cabibihan, J J
    Carrozza, M C
    A Bio-inspired approach for the design and characterization of a tactile sensory system for a cybernetic prosthetic hand2006In: Robotics and Automation: Proceedings of the 2006 IEEE International Conference on Robotics and Automation, ISSN 1050-4729, p. 1354-1358Article in journal (Refereed)
    Abstract [en]

    REcent research in prosthetic hands aims at developing innovative cybernetic systems able to allow users to feel an artificial hand as part of their bodies by providing the tactile sensation of a natural hand. Such prostheses must be endowed with artificial proprioceptive and exteroceptive sensory systems as well as appropriate neural interfaces able to exchange sensorymotor signals between the body and the nervous system of an amputee. Based on consideration of available neurophysiological and behavioral data in humans and on the specific sensory needs to control a prototypical grasp-and-lift task, two kinds of sensors were developed: on-off contact sensor arrays and triaxial force sensors. Both sensor types were characterized and compared with their biological counterparts. Their ability to convey critical information durin a lift task was evaluated with the sensors integrated in a biomechatronic cybernetic hand.

  • 33. Essick, G K
    et al.
    Edin, Benoni B
    Umeå University, Faculty of Medicine, Integrative Medical Biology, Physiology.
    Receptor encoding of moving tactile stimuli in humans. II. The mean response of individual low-threshold mechanoreceptors to motion across the receptive field.1995In: Journal of Neuroscience, ISSN 0270-6474, E-ISSN 1529-2401, Vol. 15, no 1, p. 848-864Article in journal (Refereed)
    Abstract [en]

    The mean firing rate evoked in 70 cutaneous, low-threshold mechanoreceptors in the human median, radial, and inferior alveolar nerves by stimulus motion across the skin was quantitatively studied. Moving stimuli, controlled for velocity, direction, and length of skin traversed, were provided by a servo-controlled motor that carried a brush across the receptive field. Each unit was studied with stimuli delivered at multiple velocities from 0.5 to 32 cm/sec in at least two opposing directions. A power function provided an excellent description of the MFR-versus-velocity relationship. The exponent n was interpreted to reflect the receptor's sensitivity to changes in stimulus velocity, and the multiplicative constant c, the predicted response to stimuli moving at 1.0 cm/sec. The fast adapting mechanoreceptors exhibited higher sensitivity to stimulus velocity than the slowly adapting mechanoreceptors. The mean velocity at which the fast adapting units were predicted to first respond to movement was also higher. Estimates of n, c, or both differed significantly for stimuli delivered in opposing directions for more than 70% of the mechanoreceptors. No direction of motion consistently led to power function parameters with higher values so as to suggest a "preferred" regional direction of motion for the entire population. Neither the directional difference in n nor c could be attributed to directional differences in the forces applied across the receptive fields. These findings suggest that information about velocity and direction is represented in the mean firing rate responses evoked in the population of mechanoreceptors activated by a moving tactile stimulus.

  • 34.
    Hultin, Magnus
    et al.
    Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Anaesthesiology.
    Edin, Benoni B.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Själander, Anders
    Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Medicine.
    Two Years Experiences of a new Swedish National Proficiency Test for Doctors of Medicine.2018In: Abstract book, undee, 2018Conference paper (Refereed)
  • 35.
    Hultin, Magnus
    et al.
    Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Anaesthesiology.
    Själander, Anders
    Umeå University, Faculty of Medicine, Department of Public Health and Clinical Medicine, Medicine.
    Edin, Benoni
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB).
    Warglo, Zara
    Socialstyrelsen.
    Wennberg, Åsa
    Socialstyrelsen.
    Sänkta krav på utländska läkare vore förödande2018In: Dagens Samhälle, ISSN 1652-6511, no 4 decArticle in journal (Other (popular science, discussion, etc.))
    Abstract [sv]

    Det är avgörande att det ställs samma höga krav på läkare från länder utanför EU som på svenskutbildade. Bilden av att det ställs olika krav på olika grupper vore förödande, skriver ansvariga för kunskapsprovet för läkare vid Umeå universitet ihop med Socialstyrelsen.

  • 36.
    Johansson, Anders Sixten
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Pruszynski, J Andrew
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Edin, Benoni Benjamin
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Westberg, Karl-Gunnar
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Biting intentions modulate digastric reflex responses to sudden unloading of the jaw2014In: Journal of Neurophysiology, ISSN 0022-3077, E-ISSN 1522-1598, Vol. 112, no 5, p. 1067-1073Article in journal (Refereed)
    Abstract [en]

    Reflex responses in jaw opening muscles can be evoked when a brittle object cracks between the teeth and suddenly unloads the jaw. We hypothesized that this reflex response is flexible and, as such, is modulated according to the instructed goal of biting through an object. Study participants performed two different biting tasks when holding a peanut-half stacked on a chocolate piece between their incisors. In one task, they were asked to split the peanut-half only (single-split task) and, in the other task, they were asked to split both the peanut and the chocolate in one action (double-split task). In both tasks, the peanut split evoked a jaw opening muscle response, quantified from EMG recordings of the digastric muscle in a window 20-60 ms following peanut split. Consistent with our hypothesis, we found that the jaw opening muscle response in the single-split trials was about twice the size of the jaw opening muscle response in the double-split trials. A linear model that predicted the jaw opening muscle response on a single trial basis indicated that task settings played a significant role in this modulation but also that the pre-split digastric muscle activity contributed to the modulation. These findings demonstrate that, like reflex responses to mechanical perturbations in limb muscles, reflex responses in jaw muscles not only show gain-scaling but also are modulated by subject intent.

  • 37.
    Johansson, Anders
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Westberg, Karl-Gunnar
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Edin, Benoni B.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Task-dependent control of the jaw during food splitting in humans2014In: Journal of Neurophysiology, ISSN 0022-3077, E-ISSN 1522-1598, Vol. 111, p. 2614-2623Article in journal (Refereed)
    Abstract [en]

    Although splitting of food items between the incisors often requires high bite forces, rarely do the teeth harmfully collide when the jaw quickly closes after split. Previous studies indicate that the force-velocity relationship of the jaw closing muscles principally explains the prompt dissipation of jaw closing force. Here, we asked whether people could regulate the dissipation of jaw closing force during food splitting. We hypothesized that such regulation might be implemented via differential recruitment of masseter muscle portions situated along the anteroposterior axis because these portions will experience a different shortening velocity during jaw closure. Study participants performed two different tasks when holding a peanut-half stacked on a chocolate piece between their incisors. In one task, they were asked to split the peanut-half only (single-split trials) and, in the other, to split both the peanut and the chocolate in one action (double-split trials). In double-split trials following the peanut split, the intensity of the tooth impact on the chocolate piece was on average 2.5 times greater than in single-split trials, indicating a substantially greater loss of jaw closing force in the single-split trials. We conclude that control of jaw closing force dissipation following food splitting depends on task demands. Consistent with our hypothesis, converging neurophysiological and morphometric data indicated that this control involved a differential activation of the jaw closing masseter muscle along the anteroposterior axis. These latter findings suggest that the regulation of jaw closing force after sudden unloading of the jaw exploits masseter muscle compartmentalization.

  • 38. Kanitz, Gunter
    et al.
    Cipriani, Christian
    Edin, Benoni B.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Classification of Transient Myoelectric Signals for the Control of Multi-Grasp Hand Prostheses2018In: IEEE transactions on neural systems and rehabilitation engineering, ISSN 1534-4320, E-ISSN 1558-0210, Vol. 26, no 9, p. 1756-1764Article in journal (Refereed)
    Abstract [en]

    Understanding the neurophysiological signals underlying voluntary motor control and decoding them for controlling limb prostheses is one of the major challenges in applied neuroscience and rehabilitation engineering. While pattern recognition of continuous myoelectric (EMG) signals is arguably the most investigated approach for hand prosthesis control, its underlying assumption is poorly supported, i.e., that repeated muscular contractions produce consistent patterns of steady-state EMGs. In fact, it still remains to be shown that pattern recognition-based controllers allow natural control over multiple grasps in hand prosthesis outside well-controlled laboratory settings. Here, we propose an approach that relies on decoding the intended grasp from forearm EMG recordings associated with the onset of muscle contraction as opposed to the steady-state signals. Eight unimpaired individuals and two hand amputees performed four grasping movements with a variety of arm postures while EMG recordings subsequently processed to mimic signals picked up by conventional myoelectric sensors were obtained from their forearms and residual limbs, respectively. Off-line data analyses demonstrated the feasibility of the approach also with respect to the limb position effect. The sampling frequency and length of the classified EMG window that off-line resulted in optimal performance were applied to a controller of a research prosthesis worn by one hand amputee and proved functional in real-time when operated under realistic working conditions.

  • 39. Luciw, Matthew D.
    et al.
    Jarocka, Ewa
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology. Department of Kinesiology, Faculty of Physiotherapy, University School of Physical Education, Wroclaw 51-612, Poland.
    Edin, Benoni B.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Multi-channel EEG recordings during 3,936 grasp and lift trials with varying weight and friction2014In: Scientific Data, E-ISSN 2052-4463, Vol. 1, article id 140047Article in journal (Refereed)
    Abstract [en]

    WAY-EEG-GAL is a dataset designed to allow critical tests of techniques to decode sensation, intention, and action from scalp EEG recordings in humans who perform a grasp-and-lift task. Twelve participants performed lifting series in which the object's weight (165, 330, or 660 g), surface friction (sandpaper, suede, or silk surface), or both, were changed unpredictably between trials, thus enforcing changes in fingertip force coordination. In each of a total of 3,936 trials, the participant was cued to reach for the object, grasp it with the thumb and index finger, lift it and hold it for a couple of seconds, put it back on the support surface, release it, and, lastly, to return the hand to a designated rest position. We recorded EEG (32 channels), EMG (five arm and hand muscles), the 3D position of both the hand and object, and force/torque at both contact plates. For each trial we provide 16 event times (e.g., 'object lift-off') and 18 measures that characterize the behaviour (e. g., 'peak grip force').

  • 40.
    Nordström, Anna
    et al.
    Umeå University, Faculty of Medicine, Department of Community Medicine and Rehabilitation, Rehabilitation Medicine. Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Sports Medicine.
    Edin, Benoni B.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Lindström, Sara
    Nordström, Peter
    Umeå University, Faculty of Medicine, Department of Community Medicine and Rehabilitation, Geriatric Medicine.
    Cognitive function and other risk factors for mild traumatic brain injury in young men: nationwide cohort study2013In: BMJ. British Medical Journal, E-ISSN 1756-1833, Vol. 346, p. f723-Article in journal (Refereed)
    Abstract [en]

    Objective To investigate cognitive function and other risk factors for mild traumatic brain injury in young men.

    Design Nationwide prospective cohort study.

    Setting Sweden.

    Participants 305 885 men conscripted for military service from 1989 to 1994.

    Main outcome measure mild traumatic brain injuries in relation to cognitive function and other potential risk factors assessed at conscription and follow-up.

    Results Men with one mild traumatic brain injury within two years before (n=1988) or after cognitive testing (n=2214) had about 5.5% lower overall cognitive function scores than did men with no mild traumatic brain injury during follow up (P<0.001 for both). Moreover, men with at least two mild traumatic brain injuries after cognitive testing (n=795) had 15% lower overall cognitive function scores compared with those with no such injury (P<0.001). Independent strong risk factors (P<1x10(-10)) for at least one mild traumatic brain injury after cognitive testing (n=12 494 events) included low overall cognitive function, a previous mild traumatic brain injury, hospital admission for intoxications, and low education and socioeconomic status. In a sub-cohort of twin pairs in which one twin had a mild traumatic brain injury before cognitive testing (n=63), both twins had lower logical performance and technical performance compared with men in the total cohort with no mild traumatic brain injury (P<0.05 for all).

    Conclusion Low cognitive function, intoxications, and factors related to low socioeconomic status were strong independent risk factors for mild traumatic brain injuries in men. The low cognitive function in twin pairs discordant for mild traumatic brain injury suggests a genetic component to the low cognitive function associated with such injuries. The study included only men, so inferences to women should be made with caution.

  • 41.
    Ohki, Yukari
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Edin, Benoni B
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Johansson, Roland S
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Predictions specify reactive control of individual digits in manipulation.2002In: Journal of Neuroscience, ISSN 0270-6474, E-ISSN 1529-2401, Vol. 22, no 2, p. 600-10Article in journal (Refereed)
    Abstract [en]

    When humans proactively manipulate objects, the applied fingertip forces primarily depend on feedforward, predictive neural control mechanisms that depend on internal representations of the physical properties of the objects. Here we investigate whether predictions of object properties also control fingertip forces that subjects generate reactively. We analyzed fingertip forces reactively supporting grasp stability in a restraining task that engaged two fingers. Each finger contacted a plate mounted on a separate torque motor, and, at unpredictable times, both plates were loaded simultaneously with forces tangential to the plates or just one of the plates was loaded. Thus, the apparatus acted as though the plates were mechanically linked or as though they were two independent objects. In different test series, each with a predominant behavior of the apparatus and with interspersed catch trials, we showed that the reactive responses clearly reflected the predominant behavior of the apparatus. Whether subject performed the task with one hand or bimanually, appropriate reactive fingertip forces developed when predominantly both contact plates were loaded or just one of the plates was loaded. When a finger was unexpectedly loaded during a catch trial, a weak initial reactive response was triggered, but the effective force development was delayed by approximately 100 msec. We conclude that the predicted physical properties of an object not only control fingertip forces during proactive but also in reactive manipulative tasks. Specifically, the automatic reactive responses reflect predictions at the level of individual digits as to the mechanical linkage of items contacted by the fingertips in manipulation.

  • 42.
    Panarese, Alessandro
    et al.
    Scuola Superiore Sant’Anna, Pisa.
    Edin, Benoni B
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    A modified low-cost haptic interface as a tool for complex tactile stimulation2011In: Medical Engineering and Physics, ISSN 1350-4533, E-ISSN 1873-4030, Vol. 33, no 3, p. 386-390Article in journal (Refereed)
    Abstract [en]

    This study describes the development and evaluation of a platform for the investigation of the human tactile ability. Specifically, it enables precise and reproducible application of time-varying 3D force stimuli to the skin of an immobilized human limb. We proceeded in the following steps: (1) programming a low-cost haptic interface to apply time-varying 3D force stimuli to a fixed rigid target, (2) implementing a combined feed-forward/feedback controller to improve the platform's precision and reliability in force stimulation, (3) determining the optimal tuning of the control loop parameters and (4) evaluating the system's performances when applying time-varying 3D force stimuli to an immobilized human finger pad. The system's performances were evaluated in terms of the accuracy and repeatability when delivering standard 3D force stimuli, i.e., stimuli with specified force components in the normal and skin tangential directions. Within the range of forces tested (5N in various directions), the maximum difference between the actual force and the desired value during static phases was <30mN (accuracy) and the root-mean-square of the standard deviation (repeatability) was 15mN during static phases and <75mN during dynamic phases.

  • 43.
    Panarese, Alessandro
    et al.
    Scuola Superiore Sant’Anna, Pisa.
    Edin, Benoni B
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Human ability to discriminate direction of three-dimensional force stimuli applied to the finger pad2011In: Journal of Neurophysiology, ISSN 0022-3077, E-ISSN 1522-1598, Vol. 105, no 2, p. 541-547Article in journal (Refereed)
    Abstract [en]

    Sensory information from tactile mechanoreceptors located in the glabrous skin of the hand is crucial for skillful object exploration and manipulation. These mechanoreceptors reliably encode the direction of fingertip forces, and the brain certainly relies on this information in both sensorimotor and cognitive tasks. In this study, we examined human ability to discriminate the direction of force stimuli applied to the volar surface of the index fingertip on the basis of tactile information only. We show that humans can discriminate three-dimensional (3D) force stimuli whose directions differ by an angle as small as 7.1 ° in the plane tangential to the skin surface. Moreover, we found that the discrimination ability was mainly affected by the time-varying phases of the stimulus, because adding a static plateau phase to the stimulus improved the discrimination threshold only to a limited extent.

  • 44. Panarese, Alessandro
    et al.
    Edin, Benoni B
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Vecchi, Fabrizio
    Carrozza, Maria C
    Johansson, Roland S
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Humans can integrate force feedback to toes in their sensorimotor control of a robotic hand2009In: IEEE transactions on neural systems and rehabilitation engineering, ISSN 1534-4320, E-ISSN 1558-0210, Vol. 17, no 6, p. 560-567Article in journal (Refereed)
    Abstract [en]

    Tactile sensory feedback is essential for dexterous object manipulation. Users of hand myoelectric prostheses without tactile feedback must depend essentially on vision to control their device. Indeed, improved tactile feedback is one of their main priorities. Previous research has provided evidence that conveying tactile feedback can improve prostheses control, although additional effort is required to solve problems related to pattern recognition learning, unpleasant sensations, sensory adaptation, and low spatiotemporal resolution. Still, these studies have mainly focused on providing stimulation to hairy skin regions close to the amputation site, i.e., usually to the upper arm. Here, we explored the possibility to provide tactile feedback to the glabrous skin of toes, which have mechanical and neurophysiological properties similar to the fingertips. We explored this paradigm in a grasp-and-lift task, in which healthy participants controlled two opposing digits of a robotic hand by changing the spacing of their index finger and thumb. The normal forces applied by the robotic fingertips to a test object were fed back to the right big and second toe. We show that within a few lifting trials, all the participants incorporated the force feedback received by the foot in their sensorimotor control of the robotic hand.

  • 45.
    Säfström, Daniel
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Edin, Benoni B
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Acquiring and adapting a novel audiomotor map in human grasping.2006In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 173, no 3, p. 487-497Article in journal (Refereed)
    Abstract [en]

    For sensorimotor transformations to be executed accurately, there must be mechanisms that can both establish and modify mappings between sensory and motor coordinates. Such mechanisms were investigated in normal subjects using a reach-to-grasp task. First, we replaced the normal input of visual information about object size with auditory information, i.e., we attempted to establish an 'audiomotor map'. The size of the object was log linearly related to the frequency of the sound, and we measured the maximum grip aperture (MGA) during the reaching phase to determine if the subjects had learned the relationship. Second, we changed the frequency-object size relationship to study adaptation in the newly acquired map. Our results demonstrate that learning of an audiomotor map consisted of three distinct phases: during the first stage (approximately 10-15 trials) subjects simply used MGAs large enough to grasp any reasonably sized object and there were no overt signs of learning. During the second stage, there was a period of fast learning where the slope of the relationship between MGA and object size became steeper until the third stage where the slope was constant. In contrast, when sensorimotor adaptation was studied in the established audiomotor map, there was rapid learning from the start of a size perturbation. We conclude that different learning strategies are employed when sensorimotor transformations are established compared to when existing transformations are modified.

  • 46.
    Säfström, Daniel
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Edin, Benoni B
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Prediction of object contact during grasping.2008In: Experimental brain research. Experimentelle Hirnforschung. Expérimentation cérébrale, ISSN 1432-1106, Vol. 190, no 3, p. 265-77Article in journal (Refereed)
    Abstract [en]

    The maximum grip aperture (MGA) during prehension is linearly related to the size of objects to be grasped and is adapted to the haptically sensed object size when there is a discrepancy between visual and haptic information. We have investigated what information is used to drive this adaptation process and how the onset of fingertip forces on the object is triggered. Subjects performed a reach-to-grasp task, where the object seen and the object grasped physically never were the same. We measured the movements of the index finger and the thumb and the contact forces between each fingertip and the object. The subjects' adaptation of the MGA was unrelated both to different fingertip velocities at the moment of object contact, or the fingertip forces. Instead, the 'timing' of contact between the fingers and the object was most consistently influenced by introducing a size discrepancy. Specifically, if the object was larger than expected, the moment of contact occurred earlier, and if the object was decreased in size, then the contact occurred later. During adaptation, these timing differences were markedly reduced. Also, the motor command for applying forces on the object seemed to be released in anticipation of the predicted moment of contact. We therefore conclude that the CNS dynamically predicts when contact between the fingertips and objects occur and that aperture adaptation is primarily driven by timing prediction errors.

  • 47.
    Säfström, Daniel
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Edin, Benoni B
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Short-term plasticity of the visuomotor map during grasping movements in humans.2005In: Learning & memory (Cold Spring Harbor, N.Y.), ISSN 1072-0502, E-ISSN 1549-5485, Vol. 12, no 1, p. 67-74Article in journal (Refereed)
    Abstract [en]

    During visually guided grasping movements, visual information is transformed into motor commands. This transformation is known as the "visuomotor map." To investigate limitations in the short-term plasticity of the visuomotor map in normal humans, we studied the maximum grip aperture (MGA) during the reaching phase while subjects grasped objects of various sizes. The objects seen and the objects grasped were physically never the same. When a discrepancy had been introduced between the size of the visual and the grasped objects, and the subjects were fully adapted to it, they all readily interpolated and extrapolated the MGA to objects not included in training trials. In contrast, when the subjects were exposed to discrepancies that required a slope change in the visuomotor map, they were unable to adapt adequately. They instead retained a subject-specific slope of the relationship between the visual size and MGA. We conclude from these results that during reaching for grasping, normal subjects are unable to abandon a straight linear function determining the relationship between visual object size and MGA. Moreover, the plasticity of the visuomotor map is, at least in short term, constrained to allow only offset changes, that is, only "rigid shifts" are possible between the visual and motor coordinate systems.

  • 48.
    Säfström, Daniel
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Edin, Benoni B
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Task requirements influence sensory integration during grasping in humans.2004In: Learning & memory (Cold Spring Harbor, N.Y.), ISSN 1072-0502, E-ISSN 1549-5485, Vol. 11, no 3, p. 356-363Article in journal (Refereed)
    Abstract [en]

    The sensorimotor transformations necessary for generating appropriate motor commands depend on both current and previously acquired sensory information. To investigate the relative impact (or weighting) of visual and haptic information about object size during grasping movements, we let normal subjects perform a task in which, unbeknownst to the subjects, the object seen (visual object) and the object grasped (haptic object) were never the same physically. When the haptic object abruptly became larger or smaller than the visual object, subjects in the following trials automatically adapted their maximum grip aperture when reaching for the object. This adaptation was not dependent on conscious processes. We analyzed how visual and haptic information were weighted during the course of sensorimotor adaptation. The adaptation process was quicker and relied more on haptic information when the haptic objects increased in size than when they decreased in size. As such, sensory weighting seemed to be molded to avoid prehension error. We conclude from these results that the impact of a specific source of sensory information on the sensorimotor transformation is regulated to satisfy task requirements.

  • 49.
    Säfström, Daniel
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB).
    Edin, Benoni B.
    The sensory basis for aperture adaptation during grasping movementsManuscript (Other academic)
1 - 49 of 49
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