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  • 1.
    Alstermark, Bror
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Hultborn, H
    University of Copenhagen Department of Neuroscience and Pharmacology Copenhagen N. Denmark.
    Jankowska, E
    Sahlgrenska Academy, University of Gothenburg Department of Physiology Gothenburg Sweden.
    Pettersson, L-G
    Sahlgrenska Academy, University of Gothenburg Department of Physiology Gothenburg Sweden.
    Anders Lundberg (1920-2009).2010In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 200, no 3-4, p. 193-195Article in journal (Other (popular science, discussion, etc.))
    Abstract [en]

    Anders Lundberg was one of the founding editorial board members for EBR when it began its life in 1976 under the editorship of John Eccles. He was also one of the most prolific contributors to the journal with a total of 49 papers, including a series of 16 on the topic of “integration in descending motor pathways controlling the forelimb in the cat”. He continued as an editor of the journal until volume 16 when he persuaded his younger colleague Hans Hultborn to take his place. Hans is one of the authors of the obituary. –John Rothwell

  • 2. Andrew, Churchill
    et al.
    Hopkins, Brian
    Rönnqvist, Louise
    Umeå University, Faculty of Social Sciences, Department of Psychology.
    Vogt, Stefan
    Vision of the hand and environmental context in human prehension2000In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 134, no 1, p. 81-89Article in journal (Refereed)
    Abstract [en]

    Previous findings on the role of visual contact with the hand in the control of reaching and grasping have been contradictory. Some studies have shown that such contact is largely irrelevant, while more recent ones have emphasised its importance. In contrast, information arising from the surrounding environment has received relatively little attention in the study of prehensile actions. In order to identify the roles of both sources of information, we made kinematic comparisons between three conditions. In the first, reaching was performed in a dimly lit room and compared with a second condition in which reaches in the dark, but with the thumb and first finger illuminated, were made to a luminous object. This contrast allows the effects of environmental context to be identified. A comparison between the second and a third condition, in which both vision of the hand and the environment was removed, but the object was still visually available, enabled the assessment of how and when vision of the hand plays a role. Removing environmental cues had effects both early and late in the reach, while vision of the hand was only crucial in the period after peak deceleration. In addition, removal of both sources of information resulted in larger grip apertures. Differences and similarities between our findings and those of other studies are discussed, as is the ongoing debate about the relative importance of visual feedback of the hand in the control and co-ordination of prehensile actions. We conclude with suggestions for further research based on the set-up used in the present study.

  • 3.
    Anens, Elisabeth
    et al.
    Umeå University, Faculty of Medicine, Department of Community Medicine and Rehabilitation, Physiotherapy.
    Kristensen, Bo
    Häger-Ross, Charlotte
    Umeå University, Faculty of Medicine, Department of Community Medicine and Rehabilitation, Physiotherapy. Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Reactive grip force control in persons with cerebellar stroke: effects on ipsilateral and contralateral hand2010In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 203, no 1, p. 21-30Article in journal (Refereed)
    Abstract [en]

    This study investigates the cerebellar contribution to reactive grip control by examining differences between (22-48 years) subjects with focal cerebellar lesion due to ischaemic stroke (CL) and healthy subjects (HS). The subjects used a pinch grip to grasp and restrain an instrumented handle from moving when it was subject to unpredictable load forces of different rates (2, 4, 8, 32 N/s) or amplitudes (1, 2, 4 N). The hand ipsilateral to the lesion of the cerebellar subjects showed delayed and more variable response latencies, e.g., 278 +/- 162 ms for loads delivered at 2 N/s, compared to HS 180 +/- 53 ms (P = 0.005). The CL also used a higher pre-load grip force with the ipsilateral hand, 1.6 +/- 0.8 N, than the HS, 1.3 +/- 0.6 N (P = 0.017). In addition, the contralateral hand in subjects with unilateral cerebellar stroke showed a delayed onset of the grip response compared to HS. Cerebellar lesions thus impair the reactive grip control both in the ipsilateral and contralateral hand.

  • 4.
    Athanassiadis, Tuija
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Olsson, Kurt A
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Kolta, A
    Westberg, Karl-Gunnar
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Identification of c-Fos immunoreactive brainstem neurons activated during fictive mastication in the rabbit2005In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 165, no 4, p. 478-489Article in journal (Refereed)
    Abstract [en]

    In the present study we used the expression of the c-Fos-like protein as a "functional marker" to map populations of brainstem neurons involved in the generation of mastication. Experiments were conducted on urethane-anesthetized and paralyzed rabbits. In five animals (experimental group), rhythmical bouts of fictive masticatory-like motoneuron activity (cumulative duration 60-130 min) were induced by electrical stimulation of the left cortical "masticatory area" and recorded from the right digastric motoneuron pool. A control group of five animals (non-masticatory) were treated in the same way as the experimental animals with regard to surgical procedures, anesthesia, paralysis, and survival time. To detect the c-Fos-like protein, the animals were perfused, and the brainstems were cryosectioned and processed immunocytochemically. In the experimental group, the number of c-Fos-like immunoreactive neurons increased significantly in several brainstem areas. In rostral and lateral areas, increments occurred bilaterally in the borderzones surrounding the trigeminal motor nucleus (Regio h); the rostrodorsomedial half of the trigeminal main sensory nucleus; subnucleus oralis-gamma of the spinal trigeminal tract; nuclei reticularis parvocellularis pars alpha and nucleus reticularis pontis caudalis (RPc) pars alpha. Further caudally-enhanced labeling occurred bilaterally in nucleus reticularis parvocellularis and nucleus reticularis gigantocellularis (Rgc) including its pars-alpha. Our results provide a detailed anatomical record of neuronal populations that are correlated with the generation of the masticatory motor behavior.

  • 5.
    Bowman, Miles C
    et al.
    Centre for Neuroscience Studies and Department of Psychology, Queen’s University, Kingston, ON K7L 3N6, Canada.
    Johansson, Roland S
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Flanagan, John Randall
    Centre for Neuroscience Studies and Department of Psychology, Queen’s University, Kingston, ON K7L 3N6, Canada.
    Eye-hand coordination in a sequential target contact task2009In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 195, no 2, p. 273-283Article in journal (Refereed)
    Abstract [en]

    Most object manipulation tasks involve a series of actions demarcated by mechanical contact events, and gaze is typically directed to the locations of these events as the task unfolds. Here, we examined the timing of gaze shifts relative to hand movements in a task in which participants used a handle to contact sequentially five virtual objects located in a horizontal plane. This task was performed both with and without visual feedback of the handle position. We were primarily interested in whether gaze shifts, which in our task shifted from a given object to the next about 100 ms after contact, were predictive or triggered by tactile feedback related to contact. To examine this issue, we included occasional catch contacts where forces simulating contact between the handle and object were removed. In most cases, removing force did not alter the timing of gaze shifts irrespective of whether or not vision of handle position was present. However, in about 30% of the catch contacts, gaze shifts were delayed. This percentage corresponded to the fraction of contacts with force feedback in which gaze shifted more than 130 ms after contact. We conclude that gaze shifts are predictively controlled but timed so that the hand actions around the time of contact are captured in central vision. Furthermore, a mismatch between the expected and actual tactile information related to the contact can lead to a reorganization of gaze behavior for gaze shifts executed greater than 130 ms after a contact event.

  • 6.
    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.

  • 7. 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.

  • 8.
    Domellöf, Erik
    et al.
    Umeå University, Faculty of Social Sciences, Department of Psychology.
    Rönnqvist, Louise
    Umeå University, Faculty of Social Sciences, Department of Psychology.
    Hopkins, Brian
    Functional asymmetries in the stepping response of the human newborn: a kinematic approach2007In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 177, no 3, p. 324-335Article in journal (Refereed)
    Abstract [en]

    In order to investigate subtle expressions of functional asymmetries in newborn leg movements, kinematic registrations were made on a sample of 40 healthy fullterm newborn infants during performance of the stepping response. Time–position data were collected from markers attached to the hip, knee and ankle joints of the left and right leg, and movements of both legs recorded simultaneously. Findings included evident side differences in terms of smoother trajectories of the right leg as a consequence of less movement segmentation compared to the left leg. Additionally, analyses of intralimb coordination revealed side differences with regard to stronger ankle–knee couplings and smaller phase shifts in the right leg. The findings suggest that asymmetries in newborn stepping responses are present in terms of spatio-temporal parameters and intralimb coordination. No evidence of a lateral preference in terms of frequency of the first foot moved was found. The present study adds new understanding to the lateralized attributes of the stepping response in the human newborn and as such points to new directions of research on the nature of laterality in the future.

  • 9.
    Domkin, Dmitry
    et al.
    Umeå University, Faculty of Medicine, Surgical and Perioperative Sciences, Sports Medicine.
    Laczko, Jozsef
    Djupsjöbacka, Mats
    Jaric, Slobodan
    Latash, Mark L
    Joint angle variability in 3D bimanual pointing: uncontrolled manifold analysis.2005In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 163, no 1, p. 44-57Article in journal (Refereed)
    Abstract [en]

    The structure of joint angle variability and its changes with practice were investigated using the uncontrolled manifold (UCM) computational approach. Subjects performed fast and accurate bimanual pointing movements in 3D space, trying to match the tip of a pointer, held in the right hand, with the tip of one of three different targets, held in the left hand during a pre-test, several practice sessions and a post-test. The prediction of the UCM approach about the structuring of joint angle variance for selective stabilization of important task variables was tested with respect to selective stabilization of time series of the vectorial distance between the pointer and aimed target tips (bimanual control hypothesis) and with respect to selective stabilization of the endpoint trajectory of each arm (unimanual control hypothesis). The components of the total joint angle variance not affecting (V(COMP)) and affecting (V(UN)) the value of a selected task variable were computed for each 10% of the normalized movement time. The ratio of these two components R(V)=V(COMP)/V(UN) served as a quantitative index of selective stabilization. Both the bimanual and unimanual control hypotheses were supported, however the R(V) values for the bimanual hypothesis were significantly higher than those for the unimanual hypothesis applied to the left and right arm both prior to and after practice. This suggests that the CNS stabilizes the relative trajectory of one endpoint with respect to the other more than it stabilizes the trajectories of each of the endpoints in the external space. Practice-associated improvement in both movement speed and accuracy was accompanied by counter-intuitive lack of changes in R(V). Both V(COMP) and V(UN) variance components decreased such that their ratio remained constant prior to and after practice. We conclude that the UCM approach offers a unique and under-explored opportunity to track changes in the organization of multi-effector systems with practice and allows quantitative assessment of the degree of stabilization of selected performance variables.

  • 10.
    Domkin, Dmitry
    et al.
    Umeå University, Faculty of Medicine, Surgical and Perioperative Sciences, Sports Medicine.
    Laczko, Jozsef
    Jaric, Slobodan
    Johansson, Håkan
    Latash, Mark
    Structure of joint variability in bimanual pointing tasks2002In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 143, no 1, p. 11-23Article in journal (Refereed)
    Abstract [en]

    Changes in the structure of motor variability during practicing a bimanual pointing task were investigated using the framework of the uncontrolled manifold (UCM) hypothesis. The subjects performed fast and accurate planar movements with both arms, one moving the pointer and the other moving the target. The UCM hypothesis predicts that joint kinematic variability will be structured to selectively stabilize important task variables. This prediction was tested with respect to selective stabilization of the trajectory of the endpoint of each arm (unimanual control hypotheses) and with respect to selective stabilization of the timecourse of the vectorial distance between the target and the pointer tip (bimanual control hypothesis). Components of joint position variance not affecting and affecting a mean value of a selected variable were computed at each 10% of normalized movement time. The ratio of these two components ( R(V)) served as a quantitative index of selective stabilization. Both unimanual control hypotheses and the bimanual control hypothesis were supported both prior to and after practice. However, the R(V) values for the bimanual control hypothesis were significantly higher than for either of the unimanual control hypothesis, suggesting that the bimanual synergy was not simply a simultaneous execution of two unimanual synergies. After practice, an improvement in both movement speed and accuracy was accompanied by counterintuitive changes in the structure of kinematic variability. Components of joint position variance affecting and not affecting a mean value of a selected variable decreased, but there was a significantly larger drop in the latter when applied on each of the three selected task variables corresponding to the three control hypotheses. We conclude that the UCM hypothesis allows quantitative assessment of the degree of stabilization of selected performance variables and provides information on changes in the structure of a multijoint synergy that may not be reflected in its overall performance.

  • 11.
    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.

  • 12.
    Englezou, Pavlos C.
    et al.
    University of Manchester.
    Degli Esposti, Mauro
    University of Manchester.
    Wiberg, Mikael
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Anatomy. Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Hand Surgery.
    Reid, Adam J.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Anatomy. University of Manchester.
    Terenghi, Giorgio
    University of Manchester.
    Mitochondrial involvement in sensory neuronal cell death and survival2012In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 221, no 4, p. 357-367Article in journal (Refereed)
    Abstract [en]

    Peripheral nerve injuries (PNI) are continuing to be an ever-growing socio-economic burden affecting mainly the young working population and the current clinical treatments to PNI provide a poor clinical outcome involving significant loss of sensation. Thus, our understanding of the underlying factors responsible for the extensive loss of the sensory cutaneous subpopulation in the dorsal root ganglia (DRG) that occurs following injury needs to be improved. The current investigations focus in identifying visual cues of mitochondria-related apoptotic events in the various subpopulations of sensory cutaneous neurons. Sensory neuronal subpopulations were identified using FastBlue retrograde labelling following axotomy. Specialised fluorogenic probes, MitoTracker Red and MitoTracker Orange, were employed to visualise the dynamic changes of the mitochondrial population of neurons. The results reveal a fragmented mitochondrial network in sural neurons following apoptosis, whereas a fused elongated mitochondrial population is present in sensory proprioceptive muscle neurons following tibial axotomy. We also demonstrate the neuroprotective properties of NAC and ALCAR therapy in vitro. The dynamic mitochondrial network breaks down following oxidative exposure to hydrogen peroxide (H2O2), but reinitiates fusion after NAC and ALCAR therapy. In conclusion, this study provides both qualitative and quantitative evidence of the susceptibility of sensory cutaneous sub-population in apoptosis and of the neuroprotective effects of NAC and ALCAR treatment on H2O2-challenged neurons.

  • 13.
    Hart, Andrew McKay
    et al.
    Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Hand Surgery. Blond-McIndoe Laboratories, Royal Free and University College Medical School, University Department of Surgery, Royal Free Campus, Rowland Hill Street, London, UK.
    Brännström, Thomas
    Umeå University, Faculty of Medicine, Department of Medical Biosciences, Pathology.
    Wiberg, Mikael
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Anatomy. Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Hand Surgery.
    Terenghi, Giorgio
    Blond-McIndoe Laboratories, Royal Free and University College Medical School, University Department of Surgery, Royal Free Campus, Rowland Hill Street, London, UK.
    Primary sensory neurons and satellite cells after peripheral axotomy in the adult rat: timecourse of cell death & elimination2002In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 142, no 3, p. 308-318Article in journal (Refereed)
    Abstract [en]

    The timecourse of cell death in adult dorsal root ganglia after peripheral axotomy has not been fully characterised. It is not clear whether neuronal death begins within I week of axotomy or continues beyond 2 months after axotomy. Similarly, neither the timecourse of satellite cell death in the adult, nor the effect of nerve repair has been described. L4 and L5 dorsal root ganglia were harvested at 1-14 days, 1-6 months after sciatic nerve division in the adult rat, in accordance with the Animals (Scientific Procedures) Act 1986. In separate groups the nerve was repaired either immediately or following a 1-week delay, and the ganglia were harvested 2 weeks after the initial transection. Microwave permeabilisation and triple staining enabled combined TUNEL staining, morphological examination and neuron counting by the stereological optical dissector technique. TUNEL-positive neurons, exhibiting a range of morphologies, were seen at all timepoints (peak 25 cells/group 2 weeks after axotomy) in axotomised ganglia only. TUNEL-positive satellite cell numbers peaked 2 months after axotomy and were more numerous in axotomised than control ganglia. L4 control ganglia contained 13,983 (SD 568) neurons and L5, 16,285 (SD 1,313). Neuron loss was greater in L5 than L4 axotomised ganglia, began at I week (15%, P=0.045) post-axotomy, reached 35% at 2 months (P<0.001) and was not significantly greater at 4 months or 6 months. Volume of axotomised ganglia fell to 19% of control by 6 months (P<0.001). In animals that underwent nerve repair, both the number of TUNEL-positive neurons and neuron loss were reduced. Immediate repair was more protective than repair after a 1-week delay. Thus TUNEL positivity precedes actual neuron loss, reflecting the time taken to complete cell death and elimination. Neuronal death begins within I day of peripheral axotomy, the majority occurs within the first 2 months, and limited death is still occurring at 6 months. Neuronal death is modulated by peripheral nerve repair and by its timing after axotomy. Secondary satellite cell death also occurs, peaking 2 months after axotomy. These results provide a logical framework for future research into neuronal and satellite cell death within the dorsal root ganglia and provide further insight into the process of axotomy induced neuronal death.

  • 14.
    Hart, Andrew McKay
    et al.
    Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences. Blond-McIndoe Centre, Royal Free & University College Medical School, University Department of Surgery, Royal Free Campus, Rowland Hill Street, London, NW3 2PF, UK.
    Wiberg, Mikael
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Anatomy. Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Hand Surgery.
    Youle, Mike
    Royal Free Centre for HIV Medicine, Royal Free Hospital, London, UK.
    Terenghi, Giorgio
    Blond-McIndoe Centre, Royal Free & University College Medical School, University Department of Surgery, Royal Free Campus, Rowland Hill Street, London, NW3 2PF, UK.
    Systemic acetyl-L-carnitine eliminates sensory neuronal loss after peripheral axotomy: a new clinical approach in the management of peripheral nerve trauma2002In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 145, no 2, p. 182-189Article in journal (Refereed)
    Abstract [en]

    Several hundred thousand peripheral nerve injuries occur each year in Europe alone. Largely due to the death of around 40% of primary sensory neurons, sensory outcome remains disappointingly poor despite considerable advances in surgical technique; yet no clinical therapies currently exist to prevent this neuronal death. Acetyl-L-carnitine (ALCAR) is a physiological peptide with roles in mitochondrial bioenergetic function, which may also increase binding of nerve growth factor by sensory neurons. Following unilateral sciatic nerve transection, adult rats received either one of two doses of ALCAR or sham, or no treatment. Either 2 weeks or 2 months later, L4 and L5 dorsal root ganglia were harvested bilaterally, in accordance with the Animal (Scientific Procedures) Act 1986. Neuronal death was quantified with a combination of TUNEL [TdT (terminal deoxyribonucleotidyl transferase) uptake nick end labelling] and neuron counts obtained using the optical disector technique. Sham treatment had no effect upon neuronal death. ALCAR treatment caused a large reduction in the number of TUNEL-positive neurons 2 weeks after axotomy (sham treatment 33/group; low-dose ALCAR 6/group, P=0.132; high-dose ALCAR 3/group, P<0.05), and almost eliminated neuron loss (sham treatment 21%; low-dose ALCAR 0%, P=0.007; high-dose ALCAR 2%, P<0.013). Two months after axotomy the neuroprotective effect of high-dose ALCAR treatment was preserved for both TUNEL counts (no treatment five/group; high-dose ALCAR one/group) and neuron loss (no treatment 35%; high-dose ALCAR -4%, P<0.001). These results provide further evidence for the role of mitochondrial bioenergetic dysfunction in post-traumatic sensory neuronal death, and also suggest that acetyl-L-carnitine may be the first agent suitable for clinical use in the prevention of neuronal death after peripheral nerve trauma.

  • 15.
    Holm, Linus
    et al.
    Umeå University, Faculty of Social Sciences, Department of Psychology.
    Karampela, Olympia
    Umeå University, Faculty of Social Sciences, Department of Psychology.
    Ullén, Fredrik
    Department of Neuroscience, Karolinska Institutet.
    Madison, Guy
    Umeå University, Faculty of Social Sciences, Department of Psychology.
    Executive control and working memory are involved in sub-second repetitive motor timing2017In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 235, no 3, p. 787-798Article in journal (Refereed)
    Abstract [en]

    The nature of the relationship between timing and cognition remains poorly understood. Cognitive control is known to be involved in discrete timing tasks involving durations above 1 s, but has not yet been demonstrated for repetitive motor timing below 1 s. We examined the latter in two continuation tapping experiments, by varying the cognitive load in a concurrent task. In Experiment 1, participants repeated a fixed three finger sequence (low executive load) or a pseudorandom sequence (high load) with either 524-, 733-, 1024- or 1431-ms inter-onset intervals (IOIs). High load increased timing variability for 524 and 733-ms IOIs but not for the longer IOIs. Experiment 2 attempted to replicate this finding for a concurrent memory task. Participants retained three letters (low working memory load) or seven letters (high load) while producing intervals (524- and 733-ms IOIs) with a drum stick. High load increased timing variability for both IOIs. Taken together, the experiments demonstrate that cognitive control processes influence sub-second repetitive motor timing.

  • 16.
    Holm, Linus
    et al.
    Umeå University, Faculty of Social Sciences, Department of Psychology.
    Ullén, Fredrik
    Karolinska institutet, Institutionen för kvinnor och barns hälsa, Stockholm Brain Institute.
    Madison, Guy
    Umeå University, Faculty of Social Sciences, Department of Psychology.
    Intelligence and temporal accuracy of behaviour: unique and shared associations with reaction time and motor timing2011In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 214, no 2, p. 175-183Article in journal (Refereed)
    Abstract [en]

    Intelligence is associated with accuracy in a wide range of timing tasks. One source of such associations is likely to be individual differences in top-down control, e.g. sustained attention, that influence performance in both temporal tasks and other cognitively controlled behaviors. In addition, we have studied relations between intelligence and a simple rhythmic motor task, isochronous serial interval production (ISIP), and found a substantial component of that relation, which is independent of fluctuations in top-down control. The main purpose of the present study was to investigate whether such bottom-up mechanisms are involved also in the relation between intelligence and reaction time (RT) tasks. We thus investigated if common variance between the ISIP and RT tasks underlies their respective associations with intelligence. 112 participants performed a simple RT task, a choice RT task and the ISIP task. Intelligence was assessed with the Raven SPM Plus. The analysed timing variables included mean and variability in the RT tasks and two variance components in the ISIP task. As predicted, RT and ISIP variables were associated with intelligence. The timing variables were positively intercorrelated and a principal component analysis revealed a substantial first principal component that was strongly related to all timing variables, and positively correlated with intelligence. Furthermore, a commonality analysis demonstrated that the relations between intelligence and the timing variables involved a commonality between the timing variables as well as unique contributions from choice RT and ISIP. We discuss possible implications of these findings, and argue that they support our main hypothesis, i.e. that relations between intelligence and RT tasks have a bottom-up component.

  • 17.
    Häger-Ross, Charlotte
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Cole, KJ
    Johansson, Roland S
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Grip-force responses to unanticipated object loading: load direction reveals body- and gravity-referenced intrinsic task variables1996In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 110, no 1, p. 142-150Article in journal (Refereed)
    Abstract [en]

    Humans preserve grasp stability by automatically regulating the grip forces when loads are applied tangentially to the grip surfaces of a manipulandum held in a precision grip. The effects of the direction of the load force in relation to the palm, trunk, and gravity were investigated in blindfolded subjects. Controlled, tangential load-forces were delivered in an unpredictable manner to the grip surface in contact with the index finger either in the distal and proximal directions (away from and toward the palm) or in the ulnar and radial directions (transverse to the palm). The hand was oriented in: (1) a standard position, with the forearm extended horizontally and anteriorly in intermediate pronosupination; (2) an inverted position, reversing the direction of radial and ulnar loads in relation to gravity; and (3) a horizontally rotated position, in which distal loads were directed toward the trunk. The amplitude of the grip-force responses (perpendicular to the grip surface) varied with the direction of load in a manner reflecting frictional anisotropies at the digit-object interface; that is, the subjects automatically scaled the grip responses to provide similar safety margins against frictional slips. For all hand positions, the time from onset of load increase to start of the grip-force increase was shorter for distal loads, which tended to pull the object out of the hand, than for proximal loads. Furthermore, this latency was shorter for loads in the direction of gravity, regardless of hand position. Thus, shorter latencies were observed when frictional forces alone opposed the load, while longer latencies occurred when gravity also opposed the load or when the more proximal parts of the digits and palm were positioned in the path of the load. These latency effects were due to different processing delays in the central nervous system and may reflect the preparation of a default response in certain critical directions. The response to loads in other directions would incur delays required to implement a new frictional scaling and a different muscle activation pattern to counteract the load forces. We conclude that load direction, referenced to gravity and to the hand's geometry, represents intrinsic task variables in the automatic processes that maintain a stable grasp on objects subjected to unpredictable load forces. In contrast, the grip-force safety margin against frictional slips did not vary systematically with respect to these task variables. Instead, the magnitude of the grip-force responses varied across load direction and hand orientation according to frictional differences providing similar safety margins supporting grasp stability.

  • 18.
    Häger-Ross, Charlotte
    et al.
    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.
    Nondigital afferent input in reactive control of fingertip forces during precision grip1996In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 110, no 1, p. 131-141Article in journal (Refereed)
    Abstract [en]

    Sensory inputs from the digits are important in initiating and scaling automatic reactive grip responses that help prevent frictional slips when grasped objects are subjected to destabilizing load forces. In the present study we analyzed the contribution to grip-force control from mechanoreceptors located proximal to the digits when subjects held a small manipulandum between the tips of the thumb and index finger. Loads of various controlled amplitudes and rates were delivered tangential to the grip surfaces at unpredictable times. Grip forces (normal to the grip surfaces) and the position of the manipulandum were recorded. In addition, movements of hand and arm segments were assessed by recording the position of markers placed at critical points. Subjects performed test series during normal digital sensibility and during local anesthesia of the index finger and thumb. To grade the size of movements of tissues proximal to the digits caused by the loadings, three different conditions of arm and hand support were used; (1) in the hand-support condition the subjects used the three ulnar fingers to grasp a vertical dowel support and the forearm was supported in a vacuum cast; (2) in the forearm-support condition only the forearm was supported; finally, (3) in the no-support condition the arm was free. With normal digital sensibility the size of the movements proximal to the digits had small effects on the grip-force control. In contrast, the grip control was markedly influenced by the extent of such movements during digital anesthesia. The poorest control was observed in the hand-support condition, allowing essentially only digital movements. The grip responses were either absent or attenuated, with greatly prolonged onset latencies. In the forearm and no-support conditions, when marked wrist movements took place, both the frequency and the strength of grip-force responses were higher, and the grip response latencies were shorter. However, the performance never approached normal. It is concluded that sensory inputs from the digits are dominant in reactive grip control. However, nondigital sensory input may be used for some grip control during impaired digital sensibility. Furthermore, the quality of the control during impaired sensibility depends on the extent of movements evoked by the load in the distal, unanesthetized parts of the arm. The origin of these useful sensory signals is discussed.

  • 19. Jivan, Sharmila
    et al.
    Novikova, Liudmila N
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Anatomy.
    Wiberg, Mikael
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Anatomy. Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Hand Surgery.
    Novikov, Lev N
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Anatomy.
    The effects of delayed nerve repair on neuronal survival and axonal regeneration after seventh cervical spinal nerve axotomy in adult rats.2006In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 170, no 2, p. 245-254Article in journal (Refereed)
    Abstract [en]

    It has been proposed clinically that delayed surgery after traumatic brachial plexus injury may adversely affect functional outcome. In the present experimental study the neuroprotective and growth-promoting effects of early and delayed nerve grafting following proximal seventh cervical spinal nerve (C7) axotomy were examined. The ventral branch of C7 spinal nerve was transected and axons projecting out of the proximal nerve stump were labelled with Fast Blue (FB). At the same time, the biceps brachii muscle was denervated by transecting the musculocutaneous nerve at its origin. Neuronal survival and muscle atrophy were then assessed at 1, 4, 8 and 16 weeks after permanent axotomy. In the experimental groups, a peripheral nerve graft was interposed between the transected C7 spinal nerve and the distal stump of the musculocutaneous nerve at 1 week [early nerve repair (ENR)] or 8 weeks [delayed nerve repair (DNR)] after axotomy. Sixteen weeks after nerve repair had been performed, a second tracer Fluoro-Ruby (FR) was applied distal to the graft to assess the efficacy of axonal regeneration. Counts of FB-labelled neurons revealed that axotomy did not induce any significant cell loss at 4 weeks, but 15% of motoneurons and 32% of sensory neurons died at 8 weeks after injury. At 16 weeks, the amount of cell loss in spinal cord and dorsal root ganglion (DRG) reached 29 and 50%, respectively. Both ENR and DNR prevented retrograde degeneration of spinal motoneurons and counteracted muscle atrophy, but failed to rescue sensory neurons. Due to substantial cell loss at 8 weeks, the number of FR-labelled neurons after DNR was significantly lower when compared to ENR. However, the proportion of regenerating neurons among surviving motoneurons and DRG neurons remained relatively constant indicating that neurons retained their regenerative capacity after prolonged axotomy. The results demonstrate that DNR could protect spinal motoneurons and reduce muscle atrophy, but had little effect on sensory DRG neurons. However, the efficacy of neuroprotection and axonal regeneration will be significantly affected by the amount of cell loss already presented at the time of nerve repair.

  • 20.
    Johansson, Roland S
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Häger, Charlotte
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Riso, Ronald
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Somatosensory control of precision grip during unpredictable pulling loads. II. Changes in load force rate.1992In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 89, no 1, p. 192-203Article in journal (Refereed)
    Abstract [en]

    In the previous paper regarding the somatosensory control of the human precision grip, we concluded that the elicited automatic grip force adjustments are graded by the amplitude of the imposed loads when restraining an 'active' object subjected to unpredictable pulling forces (Johansson et al. 1992a). Using the same subjects and apparatus, the present study examines the capacity to respond to imposed load forces applied at various rates. Grip and load forces (forces normal and tangential to the grip surfaces) and the position of the object in the pulling direction (distal) were recorded. Trapezoidal load force profiles with plateau amplitudes of 2 N were delivered at the following rates of loading and unloading in an unpredictable sequence: 2 N/s, 4 N/s or 8 N/s. In addition, trials with higher load rate (32 N/s) at a low amplitude (0.7 N) were intermingled. The latencies between the start of the loading and the onset of the grip force response increased with decreasing load force rate. They were 80 +/- 9 ms, 108 +/- 13 ms, 138 +/- 27 ms and 174 +/- 39 ms for the 32, 8, 4 and 2 N/s rates, respectively. These data suggested that the grip response was elicited after a given minimum latency once a load amplitude threshold was exceeded. The amplitude of the initial rapid increase of grip force (i.e., the 'catch-up' response) was scaled by the rate of the load force, whereas its time course was similar for all load rates. This response was thus elicited as a unit, but its amplitude was graded by afferent information about the load rate arising very early during the loading. The scaling of the catch-up response was purposeful since it facilitated a rapid reconciliation of the ratio between the grip and load force to prevent slips. In that sense it apparently also compensated for the varying delays between the loading phase and the resultant grip force responses. However, modification of the catch-up response may occur during its course when the loading rate is altered prior to the grip force response or very early during the catch-up response itself. Hence, afferent information may be utilized continuously in updating the response although its motor expression may be confined to certain time contingencies. Moreover, this updating may take place after an extremely short latency (45-50 ms).

  • 21.
    Johansson, Roland S
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Riso, Ronald
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Häger, Charlotte
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Bäckström, Lars
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Somatosensory control of precision grip during unpredictable pulling loads. I. Changes in load force amplitude.1992In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 89, no 1, p. 181-191Article in journal (Refereed)
    Abstract [en]

    In manipulating 'passive' objects, for which the physical properties are stable and therefore predictable, information essential for the adaptation of the motor output to the properties of the current object is principally based on 'anticipatory parameter control' using sensorimotor memories, i.e., an internal representation of the object's properties based on previous manipulative experiences. Somatosensory afferent signals only intervene intermittently according to an 'event driven' control policy. The present study is the first in a series concerning the control of precision grip when manipulating 'active' objects that exert unpredictable forces which cannot be adequately represented in a sensorimotor memory. Consequently, the manipulation may be more reliant on a moment-to-moment sensory control. Subjects who were prevented from seeing the hand used the precision grip to restrain a manipulandum with two parallel grip surfaces attached to a force motor which produced distally directed (pulling) loads tangential to the finger tips. The trapezoidal load profiles consisted of a loading phase (4 N/s), plateau phase and an unloading phase (4 N/s) returning the load force to zero. Three force amplitudes were delivered in an unpredictable sequence; 1 N, 2 N and 4 N. In addition, trials with higher load rate (32 N/s) at a low amplitude (0.7 N), were superimposed on various background loads. The movement of the manipulandum, the load forces and grip forces (normal to the grip surfaces) were recorded at each finger. The grip force automatically changed with the load force during the loading and unloading phases. However, the grip responses were initiated after a brief delay. The response to the loading phase was characterized by an initial fast force increase termed the 'catch-up' response, which apparently compensated for the response delay--the grip force adequately matched the current load demands by the end of the catch-up response. In ramps with longer lasting loading phases (amplitude greater than or equal to 2 N) the catch-up response was followed by a 'tracking' response, during which the grip force increased in parallel with load force and maintained an approximately constant force ratio that prevented frictional slips. The grip force during the hold phase was linearly related to the load force, with an intercept close to the grip force used prior to the loading. Likewise, the grip force responses evoked by the fast loadings superimposed on existing loads followed the same linear relationship.(ABSTRACT TRUNCATED AT 400 WORDS)

  • 22.
    Korotkov, Alexander
    et al.
    Umeå University, Faculty of Medicine, Surgical and Perioperative Sciences, Sports Medicine.
    Radovanovic, Sasa
    Umeå University, Faculty of Medicine, Surgical and Perioperative Sciences, Sports Medicine.
    Ljubisavljevic, Milos
    Lyskov, Eugene
    Kataeva, Galina
    Roudas, Marina
    Pakhomov, Sergey
    Thunberg, Johan
    Medvedev, Sviatoslav
    Johansson, Håkan
    Comparison of brain activation after sustained non-fatiguing and fatiguing muscle contraction: a positron emission tomography study.2005In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 163, no 1, p. 65-74Article in journal (Refereed)
    Abstract [en]

    The concept of fatigue refers to a class of acute effects that can impair motor performance, and not to a single mechanism. A great deal is known about the peripheral mechanisms underlying the process of fatigue, but our knowledge of the roles of the central structures in that process is still very limited. During fatigue, it has been shown that peripheral apparatus is capable of generating adequate force while central structures become insufficient/sub-optimal in driving them. This is known as central fatigue, and it can vary between muscles and different tasks. Fatigue induced by submaximal isometric contraction may have a greater central component than fatigue induced by prolonged maximal efforts. We studied the changes in regional cerebral blood flow (rCBF) of brain structures after sustained isometric muscle contractions of different submaximal force levels and of different durations, and compared them with the conditions observed when the sustained muscle contraction becomes fatiguing. Changes in cortical activity, as indicated by changes in rCBF, were measured using positron emission tomography (PET). Twelve subjects were studied under four conditions: (1) rest condition; (2) contraction of the m. biceps brachii at 30% of MVC, sustained for 60 s; (3) contraction at 30% of MVC, sustained for 120 s, and; (4) contraction at 50% of MVC, sustained for 120 s. The level of rCBF in the activated cortical areas gradually increased with the level and duration of muscle contraction. The fatiguing condition was associated with predominantly contralateral activation of the primary motor (MI) and the primary and secondary somatosensory areas (SI and SII), the somatosensory association area (SAA), and the temporal areas AA and AI. The supplementary motor area (SMA) and the cingula were activated bilaterally. The results show increased cortical activation, confirming that increased effort aimed at maintaining force in muscle fatigue is associated with increased activation of cortical neurons. At the same time, the activation spread to several cortical areas and probably reflects changes in both excitatory and inhibitory cortical circuits. It is suggested that further studies aimed at controlling afferent input from the muscle during fatigue may allow a more precise examination of the roles of each particular region involved in the processing of muscle fatigue.

  • 23. Lorås, H
    et al.
    Sigmundsson, H
    Talcott, JB
    Öhberg, Fredrik
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    Stensdotter, AK
    Timing continuous or discontinuous movements across effectors specified by different pacing modalities and intervals2012In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 220, no 3-4, p. 335-347Article in journal (Refereed)
    Abstract [en]

    Sensorimotor synchronization is hypothesized to arise through two different processes, associated with continuous or discontinuous rhythmic movements. This study investigated synchronization of continuous and discontinuous movements to different pacing signals (auditory or visual), pacing interval (500, 650, 800, 950 ms) and across effectors (non-dominant vs. non-dominant hand). The results showed that mean and variability of asynchronization errors were consistently smaller for discontinuous movements compared to continuous movements. Furthermore, both movement types were timed more accurately with auditory pacing compared to visual pacing and were more accurate with the dominant hand. Shortening the pacing interval also improved sensorimotor synchronization accuracy in both continuous and discontinuous movements. These results show the dependency of temporal control of movements on the nature of the motor task, the type and rate of extrinsic sensory information as well as the efficiency of the motor actuators for sensory integration.

  • 24.
    Ma, J
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Anatomy.
    Novikov, L N
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Anatomy.
    Wiberg, M
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Anatomy. Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Hand Surgery.
    Kellerth, J O
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Anatomy.
    Delayed loss of spinal motoneurons after peripheral nerve injury in adult rats: a quantitative morphological study.2001In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 139, no 2, p. 216-23Article in journal (Refereed)
    Abstract [en]

    The existence of retrograde cell death in sensory dorsal root ganglion (DRG) cells after peripheral nerve injury is well established. However, with respect to retrograde motoneuron death after peripheral nerve injury, available data are conflicting. This may partly be due to the cell counting techniques used. In the present study, quantitative morphometric methods have been used to analyse retrograde motoneuron death induced by spinal nerve injury in adult rats. For comparison, DRG cells were also included in the study. The C7 spinal nerve was transected about 10 mm distal to the DRG and exposed to the fluorescent tracer fast blue in order to retrogradely label the spinal motoneurons and DRG cells of the C7 segment. At 1-16 weeks postoperatively, the nuclei of fast-blue-labelled C7 motoneurons and DRG cells were counted in consecutive 50-microm-thick serial sections. For comparison, the physical disector technique and measurements of neuronal density were also used to calculate motoneuron number. The counts of fast-blue-labelled motoneurons revealed a delayed motoneuron loss amounting to 21% and 31% after 8 and 16 weeks, respectively (P<0.001). The remaining motoneurons exhibited 20% (P<0.05) soma atrophy. Using the physical disector technique, the motoneuron loss was 23% (P<0.001) after 16 weeks. Calculations of neuronal density in Nissl-stained sections failed to reveal any motoneuron loss, although after correction for shrinkage of the ventral horn a 14% (P<0.001) motoneuron loss was found. The fast-blue-labelled DRG neurons displayed 51% (P<0.001) cell loss after 16 weeks, and the remaining cells showed 22% (P<0.001) soma atrophy. In summary, cervical spinal nerve injury induces retrograde degeneration of both motoneurons and DRG cells. However, to demonstrate the motoneuron loss adequate techniques for cell counts have to be employed.

  • 25.
    Macefield, Vaughan G
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Häger-Ross, Charlotte
    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.
    Control of grip force during restraint of an object held between finger and thumb: responses of cutaneous afferents from the digits1996In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 108, no 1, p. 155-171Article in journal (Refereed)
    Abstract [en]

    Unexpected pulling and pushing loads exerted by an object held with a precision grip evoke automatic and graded increases in the grip force (normal to the grip surfaces) that prevent escape of the object; unloading elicits a decrease in grip force. Anesthesia of the digital nerves has shown that these grip reactions depend on sensory signals from the digits. In the present study we assessed the capacity of tactile afferents from the digits to trigger and scale the evoked grip responses. Using tungsten microelectrodes inserted percutaneously into the median nerve of awake human subjects, unitary recordings were made from ten FA I and 13 FA II rapidly adapting afferents, and 12 SA I and 18 SA II slowly adapting afferents. While the subject held a manipulandum between a finger and the thumb, tangential load forces were applied to the receptor-bearing digit (index, middle, or ring finger or thumb) as trapezoidal load-force profiles with a plateau amplitude of 0.5-2.0 N and rates of loading and unloading at 2-8 N/s, or as "step-loads" of 0.5 N delivered at 32 N/s. Such load trials were delivered in both the distal (pulling) and proximal (pushing) direction. FA I afferents responded consistently to the load forces, being recruited during the loading and unloading phases. During the loading ramp the ensemble discharge of the FA I afferents reflected the first time-derivative of the load force (i.e., the load-force rate). These afferents were relatively insensitive to the subject's grip force responses. However, high static finger forces appeared to suppress excitation of these afferents during the unloading phase. The FA II afferents were largely insensitive to the load trials: only with the step-loads did some afferents respond. Both classes of SA afferents were sensitive to load force and grip force, and discharge rates were graded by the rate of loading. The firing of the SA I afferents appeared to be relatively more influenced by the subject's grip-force response than the discharge of the SA II afferents, which were more influenced by the load-force stimulus. The direction in which the tangential load force was applied to the skin influenced the firing of most afferents and in particular the SA II afferents. Individual afferents within each class (except for the FA IIs) responded to the loading ramp before the onset of the subject's grip response and may thus be responsible for initiating the automatic increase in grip force. However, nearly half of the FA I afferents recruited by the load trials responded to the loading phase early enough to trigger the subject's grip-force response, whereas only ca. one-fifth of the SA Is and SA IIs did so. These observations, together with the high density of FA I receptors in the digits, might place the FA I afferents in a unique position to convey the information required to initiate and scale the reactive grip-force responses to the imposed load forces.

  • 26.
    Macefield, Vaughan G
    et al.
    Prince of Wales Medical Research Institute, UNSW, Barker St., Randwick, Sydney.
    Johansson, Roland S
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Loads applied tangential to a fingertip during an object restraint task can trigger short-latency as well as long-latency EMG responses in hand muscles.2003In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 152, no 2, p. 143-149Article in journal (Refereed)
    Abstract [en]

    Electrical stimulation of the digital nerves can cause short- and long-latency increases in electromyographic activity (EMG) of the hand muscles, but mechanical stimulation of primarily tactile afferents in the digits generally evokes only a long-latency increase in EMG. To examine whether such stimuli can elicit short-latency reflex responses, we recorded EMG over the first dorsal interosseous muscle when subjects (n=13) used the tip of the right index finger to restrain a horizontally oriented plate from moving when very brisk tangential forces were applied in the distal direction. The plate was subjected to ramp-and-hold pulling loads at two intensities (a 1-N load applied at 32 N/s or a 2-N load applied at 64 N/s) at times unpredictable to the subjects (mean interval 2 s; trial duration 500 ms). The contact surface of the manipulandum was covered with rayon--a slippery material. For each load, EMG was averaged for 128 consecutive trials with reference to the ramp onset. In all subjects, an automatic increase in grip force was triggered by the loads applied at 32 N/s; the mean onset latency of the EMG response was 59.8 +/- 0.9 (mean +/- SE) ms. In seven subjects (54%) this long-latency response was preceded by a weak short-latency excitation at 34.6 +/- 2.9 ms. With the loads applied at 64 N/s, the long-latency response occurred slightly earlier (58.9 +/- 1.7 ms) and, with one exception, all subjects generated a short-latency EMG response (34.9 +/- 1.3 ms). Despite the higher background grip force that subjects adopted during the stronger loads (4.9 +/- 0.3 N vs 2.5 +/- 0.2 N), the incidence of slips was higher--the manipulandum escaped from the grasp in 37 +/- 5% of trials with the 64 N/s ramps, but in only 18 +/- 4% with the 32-N/s ramps. The deformation of the fingertip caused by the tangential load, rather than incipient or overt slips, triggered the short-latency responses because such responses occurred even when the finger pad was fixed to the manipulandum with double-sided adhesive tape so that no slips occurred.

  • 27.
    Madison, Guy
    et al.
    Umeå University, Faculty of Social Sciences, Department of Psychology.
    Deligniéres, Didier
    EA 29991, Faculty of Sport Sciences, University Montpellier I, Montepellier, France.
    Auditory feedback affects the long-range correlation of isochronous serial interval production: support for a closed-loop or memory model of timing2009In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 193, no 4, p. 519-527Article in journal (Refereed)
    Abstract [en]

    Long-range dependence is a characteristic property of successively produced time intervals, such as in un-paced or continuation tapping. We hypothesise in the present paper that serial dependence in such tasks could be related to a closed-loop regulation process, in which the current interval is determined by preceding ones. As a consequence, the quality of sensory feedback is likely to affect serial dependence. An experiment with human participants shows that diminished sensory information tends to increase the Hurst exponent for short inter-onset intervals and tends to decrease it for long intervals. A simulation shows that a simple auto-regressive model, whose order depends on the ratio between the inter-onset interval and an assumed temporal integration span, is able to account for most of our empirical results, including the duration specificity of long-range correlation.

  • 28.
    Pruszynski, J. Andrew
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology. Queen’s University, Kingston.
    Scott, Stephen H.
    Queen’s University, Kingston.
    Optimal feedback control and the long-latency stretch response2012In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 218, no 3, p. 341-359Article, review/survey (Refereed)
    Abstract [en]

    There has traditionally been a separation between voluntary control processes and the fast feedback responses which follow mechanical perturbations (i.e., stretch "reflexes"). However, a recent theory of motor control, based on optimal control, suggests that voluntary motor behavior involves the sophisticated manipulation of sensory feedback. We have recently proposed that one implication of this theory is that the long-latency stretch "reflex", like voluntary control, should support a rich assortment of behaviors because these two processes are intimately linked through shared neural circuitry including primary motor cortex. In this review, we first describe the basic principles of optimal feedback control related to voluntary motor behavior. We then explore the functional properties of upper-limb stretch responses, with a focus on how the sophistication of the long-latency stretch response rivals voluntary control. And last, we describe the neural circuitry that underlies the long-latency stretch response and detail the evidence that primary motor cortex participates in sophisticated feedback responses to mechanical perturbations.

  • 29.
    Radovanovic, S.
    et al.
    Umeå University, Faculty of Medicine, Surgical and Perioperative Sciences, Sports Medicine.
    Korotkov, A.
    Umeå University, Faculty of Medicine, Surgical and Perioperative Sciences, Sports Medicine.
    Johansson, H.
    Ljubisavljevic, M.
    Lyskov, E.
    Thunberg, J.
    Umeå University, Faculty of Medicine, Surgical and Perioperative Sciences, Sports Medicine.
    Kataeva, G.
    Danko, S.
    Roudas, M.
    Pakhomov, S.
    Medvedev, S.
    Comparison of brain activity during different types of proprioceptive inputs: a positron emission tomography study2002In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 143, no 3, p. 276-285Article in journal (Refereed)
    Abstract [en]

    It has been shown that the primary and secondary somatosensory cortex, as well as the supplementary motor area (SMA), are involved in central processing of proprioceptive signals during passive and active arm movements. However, it is not clear whether different cortical areas are involved in processing of different proprioceptive inputs (skin, joint, muscle receptors), what their relative contributions might be, where kinesthetic sensations are formed within the CNS, and how they interact when the full peripheral proprioceptive machinery acts. In this study we investigated the representation of the brain structures involved in the perception of passive limb movement and illusory movement generated by muscle tendon vibration. Changes in cortical activity as indicated by changes in regional cerebral blood flow (rCBF) were measured using positron emission tomography (PET). Twelve subjects were studied under four conditions: (1) passive flexion-extension movement (PM) of the left forearm; (2) induced illusions of movements (VI) similar to the real PM, induced by alternating vibration of biceps and triceps tendons (70-80 Hz) at the elbow; (3) alternating vibration of biceps and triceps tendons (with 20-50 Hz) without induced kinesthetic illusions (VN); and (4) rest condition (RE). The results show different patterns of cortex activation. In general, the activation during passive movement was higher in comparison with both kinds of vibration, and activation during vibrations with induced illusions of movement was more prominent than during vibrations without induced illusions. When the PM condition was contrasted with the other conditions we found the following areas of activation -- the primary motor (MI) and somatosensory area (SI), the SMA and the supplementary somatosensory area (SSA). In conditions where passive movements and illusory movements were contrasted with rest, some temporal areas, namely primary and associative auditory cortex, were activated, as well as secondary somatosensory cortex (SII). Our data show that different proprioceptive inputs, which induce sensation of movement, are associated with differently located activation patterns in the SI/MI and SMA areas of the cortex. In general, the comparison of activation intensities under different functional conditions indicates the involvement of SII in stimulus perception generation and of the SI/MI and SMA areas in the processing of proprioceptive input. Activation of the primary and secondary auditory cortex might reflect the interaction between somatosensory and auditory systems in movement sense generation. SSA might also be involved in movement sense generation and/or maintenance.

  • 30. Reichelt, Andreas F
    et al.
    Ash, Alyssa M
    Baugh, Lee A
    Johansson, Roland S
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB), Physiology.
    Flanagan, J Randall
    Adaptation of lift forces in object manipulation through action observation.2013In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 228, no 2, p. 221-234Article in journal (Refereed)
    Abstract [en]

    The ability to predict accurately the weights of objects is essential for skilled and dexterous manipulation. A potentially important source of information about object weight is through the observation of other people lifting objects. Here, we tested the hypothesis that when watching an actor lift an object, people naturally learn the object's weight and use this information to scale forces when they subsequently lift the object themselves. Participants repeatedly lifted an object in turn with an actor. Object weight unpredictably changed between 2 and 7 N every 5th to 9th of the actor's lifts, and the weight lifted by the participant always matched that previously lifted by the actor. Even though the participants were uninformed about the structure of the experiment, they appropriately adapted their lifting force in the first trial after a weight change. Thus, participants updated their internal representation about the object's weight, for use in action, when watching a single lift performed by the actor. This ability presumably involves the comparison of predicted and actual sensory information related to actor's actions, a comparison process that is also fundamental in action.

  • 31.
    Rönnqvist, Louise
    et al.
    Umeå University, Faculty of Social Sciences, Department of Psychology.
    Hopkins, Brian
    Motor asymmetries in the human newborn are state dependent but independent of position in space2000In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 134, no 3, p. 378-384Article in journal (Refereed)
    Abstract [en]

    Human newborns have a preference for turning and maintaining the head to one side of the body. Most studies confirm a right-sided preference in supine. Few have addressed the state dependency of this lateral bias, and even fewer have examined whether it is also expressed in the semi-upright position. We investigated whether it varies as a function of behavioural state and position in space. Kinematic recordings of head movements were made with the newborn secured on a platform in the supine or semi-upright position, which alleviated biomechanical and postural constraints imposed by gravity. Newborns differed as to whether they had a vertex, Caesarean or breech delivery. The majority of infants maintained a right-sided preference in both positions, but it was strongly mediated by state. Delivery type did not account for any lateral bias. These findings provide convincing evidence that a lateral bias in movement and positioning of the head are reflections of active neural processes rooted in the regulation of state.

  • 32. Stensdotter, A.
    et al.
    Pedersen, N.
    Wanvik, A.
    Öhberg, Fredrik
    Umeå University, Faculty of Medicine, Department of Radiation Sciences, Radiation Physics.
    Flovig, J. C.
    Fors, E. A.
    Upper body 3-dimensional kinematics during gait in psychotic patients: a pilot-study2012In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 221, no 4, p. 393-401Article in journal (Refereed)
    Abstract [en]

    Gait is recognized as a key item related to mental function. Anomalous gait in psychotic individuals has been described for the lower extremities, whereas irregularities for upper body dynamics are not described, explained or verified with unbiased methods. Reduced walking velocity and increased somatic tension defined in this patient category may influence upper body dynamics during gait. The aim of this pilot-study was to describe upper body kinematics and investigate the biomechanical association with walking velocity and muscle tension. Twelve inpatients in a psychiatric ward with first-episode psychosis and 18 healthy control subjects walked at different self-chosen velocities. Movement and walking velocity were registered, and 3D kinematics was analysed for thorax and shoulder joint. Time-synchronized EMG from the trapezius muscle, chosen as indicator for general somatic tension, was analysed for maximal amplitude and variability. Results showed that patients walked with reduced arm swing at the shoulder joint and increased lateral thorax movements. Thorax rotations about the vertical axis, walking velocity and EMG measures were similar in patients and healthy subjects. The present study could not provide a biomechanical explanation for kinematic findings based on walking velocity or somatic tension.

  • 33.
    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.

  • 34.
    Welin, Dag
    et al.
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB).
    Novikova, Liudmila
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB).
    Wiberg, Mikael
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB). Umeå University, Faculty of Medicine, Department of Surgical and Perioperative Sciences, Hand Surgery.
    Kellerth, Jan-Olof
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB).
    Novikov, Lev
    Umeå University, Faculty of Medicine, Department of Integrative Medical Biology (IMB).
    Survival and regeneration of cutaneous and muscular afferent neurons after peripheral nerve injury in adult rats2008In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 186, p. 315-323Article in journal (Refereed)
    Abstract [en]

    Peripheral nerve injury induces the retrograde degeneration of dorsal root ganglion (DRG) cells, which affects predominantly the small-diameter cutaneous afferent neurons. This study compares the time-course of retrograde cell death in cutaneous and muscular DRG cells after peripheral nerve transection as well as neuronal survival and axonal regeneration after primary repair or nerve grafting. For comparison, spinal motoneurons were also included in the study. Sural and medial gastrocnemius DRG neurons were retrogradely labeled with the fluorescent tracers Fast Blue (FB) or Fluoro-Gold (FG) from the homonymous transected nerves. Survival of labeled sural and gastrocnemius DRG cells was assessed at 3 days and 1-24 weeks after axotomy. To evaluate axonal regeneration, the sciatic nerve was transected proximally at 1 week after FB-labeling of the sural and medial gastrocnemius nerves and immediately reconstructed using primary repair or autologous nerve grafting. Twelve weeks later, the fluorescent tracer Fluoro-Ruby (FR) was applied 10 mm distal to the sciatic lesion in order to double-label sural and gastrocnemius neurons that had regenerated across the repair site. Counts of labeled gastrocnemius DRG neurons did not reveal any significant retrograde cell death after nerve transection. In contrast, sural axotomy induced a delayed loss of sural DRG cells, which amounted to 22% at 4 weeks and 43-48% at 8-24 weeks postoperatively. Proximal transection of the sciatic nerve at 1 week after injury to the sural or gastrocnemius nerves neither further increased retrograde DRG degeneration, nor did it affect survival of sural or gastrocnemius motoneurons. Primary repair or peripheral nerve grafting supported regeneration of 53-60% of the spinal motoneurons and 47-49% of the muscular DRG neurons at 13 weeks postoperatively. In the cutaneous DRG neurons, primary repair or peripheral nerve grafting increased survival by 19-30% and promoted regeneration of 46-66% of the cells. The present results suggest that cutaneous DRG neurons are more sensitive to peripheral nerve injury than muscular DRG cells, but that their regenerative capacity does not differ from that of the latter cells. However, the retrograde loss of cutaneous DRG cells taking place despite immediate nerve repair would still limit the recovery of cutaneous sensory functions.

  • 35.
    Wiesinger, Birgitta
    et al.
    Umeå University, Faculty of Medicine, Department of Odontology.
    Häggman-Henrikson, Birgitta
    Umeå University, Faculty of Medicine, Department of Odontology.
    Wänman, Anders
    Umeå University, Faculty of Medicine, Department of Odontology. Wänman.
    Lindkvist, Marie
    Umeå University, Faculty of Medicine, Department of Radiation Sciences.
    Hellström, F
    Jaw-opening accuracy is not affected by masseter muscle vibration in healthy men2014In: Experimental Brain Research, ISSN 0014-4819, E-ISSN 1432-1106, Vol. 232, no 11, p. 3501-3508Article in journal (Refereed)
    Abstract [en]

    There is a functional integration between the jaw and neck regions with head extension-flexion movements during jaw-opening/closing tasks. We recently reported that trigeminal nociceptive input by injection of hypertonic saline into the masseter muscle altered this integrated jaw-neck function during jaw-opening/closing tasks. Thus, in jaw-opening to a predefined position, the head-neck component increased during pain. Previous studies have indicated that muscle spindle stimulation by vibration of the masseter muscle may influence jaw movement amplitudes, but the possible effect on the integrated jaw-neck function is unknown. The aim of this study was to investigate the effect of masseter muscle vibration on jaw-head movements during a continuous jaw-opening/closing task to a target position. Sixteen healthy men performed two trials without vibration (Control) and two trials with bilateral masseter muscle vibration (Vibration). Movements of the mandible and the head were registered with a wireless three-dimensional optoelectronic recording system. Differences in jaw-opening and head movement amplitudes between Control and Vibration, as well as achievement of the predefined jaw-opening target position, were analysed with Wilcoxon's matched pairs test. No significant group effects from vibration were found for jaw or head movement amplitudes, or in the achievement of the target jaw-opening position. A covariation between the jaw and head movement amplitudes was observed. The results imply a high stability for the jaw motor system in a target jaw-opening task and that this task was achieved with the head-neck and jaw working as an integrated system.

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