Important features of the kinetics and kinematics of human object grasping and manipulation have been characterized, providing significant insight into how the Central Nervous System controls the hand. However, the underlying neural mechanisms that regulate the activity of multiple hand muscles are not yet well understood. This gap in our understanding of hand control has significant clinical implications for rehabilitation of hand function following neurological injury such as stroke. In our previous work we focused on correlated neural input to hand muscles to quantify the neural bases of force coordination during object grasping. We found that correlated neural input is distributed in a muscle-pair specific fashion, i.e., the neural coupling between certain muscle pairs is stronger than that between other muscle pairs. However, within this distribution, the strength of neural coupling of given muscle pairs could be modulated to task conditions. Yet, these results were obtained from a relatively small number of muscles and limited range of task conditions (grip type and object center of mass).
The aim of the present study is to determine the neural mechanisms underlying a crucial aspect of hand control: the modulation of digit force direction. To attain this objective we will quantify the modulation of (a) EMG amplitude and (b) correlated neural input (coherence) of all muscles of the thumb, index and middle fingers as a function of digit force direction. Our working hypotheses are that (1) a force-direction dependent modulation of coherence between two muscles will occur as the relative force contribution of a given muscle to the modulation of fingertip force direction changes and (2) coherence modulation will occur within an invariant distribution of correlated neural input among hand muscle pairs. These hypotheses will be tested through one-digit force production tasks and multi-digit grasping tasks (Aim#1 and #2, respectively). The outcomes of our experiments will establish how motor commands controlling groups of hand muscles are modulated as a function of force direction and task constraints. Our data are expected to improve our understanding of the control of prehension, specifically the principles underlying fundamental mechanisms of synergistic control of hand muscles for object grasping and manipulation. Relevance to public health: We believe that this knowledge will be beneficial to rehabilitation and restoration of hand function as well as to the field of neuroprosthetics.

National Institute of Health (NIH)
National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
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Motor Function, Speech and Rehabilitation Study Section (MFSR)
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Panagis, James S
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Arizona State University-Tempe Campus
Schools of Arts and Sciences
United States
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Jesunathadas, Mark; Laitano, Juan; Hamm, Thomas M et al. (2013) Across-muscle coherence is modulated as a function of wrist posture during two-digit grasping. Neurosci Lett 553:68-71
Chattopadhyay, Rita; Jesunathadas, Mark; Poston, Brach et al. (2012) A subject-independent method for automatically grading electromyographic features during a fatiguing contraction. IEEE Trans Biomed Eng 59:1749-57
Johnston, Jamie A; Bobich, Lisa R; Santello, Marco (2010) Coordination of intrinsic and extrinsic hand muscle activity as a function of wrist joint angle during two-digit grasping. Neurosci Lett 474:104-8
Johnston, Jamie A; Formicone, Gabriele; Hamm, Thomas M et al. (2010) Assessment of across-muscle coherence using multi-unit vs. single-unit recordings. Exp Brain Res 207:269-82
Danna-Dos Santos, Alessander; Poston, Brach; Jesunathadas, Mark et al. (2010) Influence of fatigue on hand muscle coordination and EMG-EMG coherence during three-digit grasping. J Neurophysiol 104:3576-87
Poston, Brach; Danna-Dos Santos, Alessander; Jesunathadas, Mark et al. (2010) Force-independent distribution of correlated neural inputs to hand muscles during three-digit grasping. J Neurophysiol 104:1141-54
Johnston, Jamie A; Winges, Sara A; Santello, Marco (2009) Neural control of hand muscles during prehension. Adv Exp Med Biol 629:577-96
Winges, Sara A; Johnston, Jamie A; Santello, Marco (2006) Muscle-pair specific distribution and grip-type modulation of neural common input to extrinsic digit flexors. J Neurophysiol 96:1258-66
Winges, Sara A; Santello, Marco (2005) From Single Motor Unit Activity to Multiple Grip Forces: Mini-review of Multi-digit Grasping. Integr Comp Biol 45:679-682
Johnston, Jamie A; Winges, Sara A; Santello, Marco (2005) Periodic modulation of motor-unit activity in extrinsic hand muscles during multidigit grasping. J Neurophysiol 94:206-18

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