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Publications (6 of 6) Show all publications
Papaioannou, S. & Dimitriou, M. (2020). Muscle spindle function in muscular dystrophy: A potential target for therapeutic intervention. Journal of Physiology, 598(8), 1433-1434
Open this publication in new window or tab >>Muscle spindle function in muscular dystrophy: A potential target for therapeutic intervention
2020 (English)In: Journal of Physiology, ISSN 0022-3751, E-ISSN 1469-7793, Vol. 598, no 8, p. 1433-1434Article in journal, Editorial material (Other academic) Published
Place, publisher, year, edition, pages
John Wiley & Sons, 2020
Keywords
dystrophin, muscular dystrophy, muscle spindle, proprioception
National Category
Physiology
Identifiers
urn:nbn:se:umu:diva-169748 (URN)10.1113/JP279611 (DOI)000521852300001 ()32128822 (PubMedID)
Note

This Perspectives article highlights an article by Gerwin et al. To read this paper, visit https://doi.org/10.1113/JP278563.

Available from: 2020-05-13 Created: 2020-05-13 Last updated: 2020-05-13Bibliographically approved
Dimitriou, M. (2018). Task-Dependent Modulation of Spinal and Transcortical Stretch Reflexes Linked to Motor Learning Rate. Behavioral Neuroscience, 132(3), 194-209
Open this publication in new window or tab >>Task-Dependent Modulation of Spinal and Transcortical Stretch Reflexes Linked to Motor Learning Rate
2018 (English)In: Behavioral Neuroscience, ISSN 0735-7044, E-ISSN 1939-0084, Vol. 132, no 3, p. 194-209Article in journal (Refereed) Published
Abstract [en]

It is generally believed that task-dependent control of body configuration ("posture") is achieved by adjusting voluntary motor activity and transcortical "long-latency" reflexes. Spinal monosynaptic circuits are thought not to be engaged in such task-level control. Similarly, being in a state of motor learning has been strongly associated only with an upregulation of feedback responses at transcortical latencies and beyond. In two separate experiments, the current study examined the task-dependent modulation of stretch reflexes by perturbing the hand of human subjects while they were waiting for a "Go" signal to move at the different stages of a classic kinematic learning task (visuomotor rotation). Although the subjects had to resist all haptic perturbations equally across task stages, the study leveraged that task-dependent feedback controllers may already be "loaded" at the movement anticipation stage. In addition to an upregulation of reflex gains during early exposure to the visual distortion, I found a relative inhibition of reflex responses in the "washout" stage (sensory realignment state). For more distal muscles (brachioradialis) this inhibition also extended to the monosynaptic reflex response ("R1"). Moreover, these R1 gains reflected individual motor learning performance in the visuomotor task. The results demonstrate that the system's "control policy" in visuomotor adaptation can also include inhibition of proprioceptive reflexes, and that aspects of this policy can affect monosynaptic spinal circuits. The latter finding suggests a novel form of state-related control, probably realized by independent control of fusimotor neurons, through which segmental circuits can tune to higher-level features of a sensorimotor task.

Place, publisher, year, edition, pages
American Psychological Association (APA), 2018
Keywords
motor learning, stretch reflex, visuomotor, task-dependent, monosynaptic
National Category
Neurosciences
Identifiers
urn:nbn:se:umu:diva-149011 (URN)10.1037/bne0000241 (DOI)000433184400007 ()29809047 (PubMedID)2-s2.0-85047665996 (Scopus ID)
Available from: 2018-06-15 Created: 2018-06-15 Last updated: 2018-06-15Bibliographically approved
Dimitriou, M. (2016). Enhanced Muscle Afferent Signals during Motor Learning in Humans. Current Biology, 26(8), 1062-1068
Open this publication in new window or tab >>Enhanced Muscle Afferent Signals during Motor Learning in Humans
2016 (English)In: Current Biology, ISSN 0960-9822, E-ISSN 1879-0445, Vol. 26, no 8, p. 1062-1068Article in journal (Refereed) Published
Abstract [en]

Much has been revealed concerning human motor learning at the behavioral level [1, 2], but less is known about changes in the involved neural circuits and signals. By examining muscle spindle responses during a classic visuomotor adaptation task [3-6] performed by fully alert humans, I found substantial modulation of sensory afferent signals as a function of adaptation state. Specifically, spindle control was independent of concurrent muscle activity but was specific to movement direction (representing muscle lengthening versus shortening) and to different stages of learning. Increased spindle afferent responses to muscle stretch occurring early during learning reflected individual error size and were negatively related to subsequent antagonist activity (i.e., 60-80 ms thereafter). Relative increases in tonic afferent output early during learning were predictive of the subjects' adaptation rate. I also found that independent spindle control during sensory realignment (the "washout" stage) induced afferent signal "linearization" with respect to muscle length (i.e., signals were more tuned to hand position). The results demonstrate for the first time that motor learning also involves independent and state-related modulation of sensory mechanoreceptor signals. The current findings suggest that adaptive motor performance also relies on the independent control of sensors, not just of muscles. I propose that the "gamma" motor system innervating spindles acts to facilitate the acquisition and extraction of task-relevant information at the early stages of sensorimotor adaptation. This designates a more active and targeted role for the human proprioceptive system during motor learning.

National Category
Cell and Molecular Biology Neurosciences
Identifiers
urn:nbn:se:umu:diva-121577 (URN)10.1016/j.cub.2016.02.030 (DOI)000375339700025 ()27040776 (PubMedID)
Available from: 2016-06-27 Created: 2016-06-03 Last updated: 2018-06-07Bibliographically approved
Dimitriou, M. (2014). Human Muscle Spindle Sensitivity Reflects the Balance of Activity between Antagonistic Muscles. Paper presented at INICAL NEUROPHYSIOLOGY, V109, P360 uszynski J. Andrew, 2009, JOURNAL OF NEUROPHYSIOLOGY, V102, P992. Journal of Neuroscience, 34(41), 13644-13655
Open this publication in new window or tab >>Human Muscle Spindle Sensitivity Reflects the Balance of Activity between Antagonistic Muscles
2014 (English)In: Journal of Neuroscience, ISSN 0270-6474, E-ISSN 1529-2401, Vol. 34, no 41, p. 13644-13655Article in journal (Refereed) Published
Abstract [en]

Muscle spindles are commonly considered as stretch receptors encoding movement, but the functional consequence of their efferent control has remained unclear. The "alpha-gamma coactivation" hypothesis states that activity in a muscle is positively related to the output of its spindle afferents. However, in addition to the above, possible reciprocal inhibition of spindle controllers entails a negative relationship between contractile activity in one muscle and spindle afferent output from its antagonist. By recording spindle afferent responses from alert humans using microneurography, I show that spindle output does reflect antagonistic muscle balance. Specifically, regardless of identical kinematic profiles across active finger movements, stretch of the loaded antagonist muscle (i.e., extensor) was accompanied by increased afferent firing rates from this muscle compared with the baseline case of no constant external load. In contrast, spindle firing rates from the stretching antagonist were lowest when the agonist muscle powering movement (i.e., flexor) acted against an additional resistive load. Stepwise regressions confirmed that instantaneous velocity, extensor, and flexor muscle activity had a significant effect on spindle afferent responses, with flexor activity having a negative effect. Therefore, the results indicate that, as consequence of their efferent control, spindle sensitivity (gain) to muscle stretch reflects the balance of activity between antagonistic muscles rather than only the activity of the spindle-bearing muscle.

Keywords
afferent, motor control, muscle spindle, proprioception, reflex, sense of agency
National Category
Medical and Health Sciences
Identifiers
urn:nbn:se:umu:diva-96611 (URN)10.1523/JNEUROSCI.2611-14.2014 (DOI)000343142100008 ()
Conference
INICAL NEUROPHYSIOLOGY, V109, P360 uszynski J. Andrew, 2009, JOURNAL OF NEUROPHYSIOLOGY, V102, P992
Available from: 2014-11-27 Created: 2014-11-24 Last updated: 2018-06-07Bibliographically approved
Dimitriou, M. & Edin, B. B. (2010). Human muscle spindles act as forward sensory models. Current Biology, 20(19), 1763-1767
Open this publication in new window or tab >>Human muscle spindles act as forward sensory models
2010 (English)In: Current Biology, ISSN 0960-9822, E-ISSN 1879-0445, Vol. 20, no 19, p. 1763-1767Article in journal (Refereed) Published
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.

Keywords
proprioceptive feedback; electrical-stimulation; afferent-fibers; vibration; movement; integration; discharges; hindlimb; system; task
National Category
Cell and Molecular Biology
Identifiers
urn:nbn:se:umu:diva-42243 (URN)10.1016/j.cub.2010.08.049 (DOI)000283041300031 ()20850322 (PubMedID)
Available from: 2011-04-06 Created: 2011-04-06 Last updated: 2018-06-08Bibliographically approved
Dimitriou, M. & Edin, B. B. (2008). Discharges in Human Muscle Receptor Afferents during Block Grasping. Journal of Neuroscience, 28(48), 12632-12642
Open this publication in new window or tab >>Discharges in Human Muscle Receptor Afferents during Block Grasping
2008 (English)In: Journal of Neuroscience, ISSN 0270-6474, E-ISSN 1529-2401, Vol. 28, no 48, p. 12632-12642Article in journal (Refereed) Published
National Category
Physiology
Identifiers
urn:nbn:se:umu:diva-3744 (URN)10.1523/JNEUROSCI.3357-08.2008 (DOI)19036957 (PubMedID)
Available from: 2009-01-09 Created: 2009-01-09 Last updated: 2018-06-09Bibliographically approved
Organisations
Identifiers
ORCID iD: ORCID iD iconorcid.org/0000-0001-9890-2974

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