Cortical control of a proximo-distal muscle synergy in humans

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The American neurologist and science writer Richard E Cytowic described in his book titled 'The man who tasted shapes', that the brain was as a "distributed system" where "the many aspects of complex functions subserved by a particular circuit are not rigidly located in any one of its segments but rather in the dominant process occurring at any given time in the circuit itself". The experimental studies described here are thus aimed at understanding further how this dominant process of human brain is like and more precisely, how it works for muscle coordination and synergy. It is question of brain functional connectivity to control interjoint movement (synergy) and the current grant enlarges the focus on the developmental aspect of such a control. Besides, this basic work will be of major importance to broaden our knowledge of the brain connectivity - related potential of reorganization (plasticity) following a lesion in adults or due to a preterm birth history in school-aged children. To this end, healthy adults and healthy school-aged (8-10 yr) children born full-term will participate. The experiments will test whether connections within brain structures and between brain and cerebellum are involved in the control of a proximo-distal muscle synergy. The experimental model we are used to work with is namely a precision grip task with superimposed cyclic wrist movements. Standardized paradigms of transcranial magnetic stimulation (TMS) will be applied (single, paired-pulse, repetitive) to test the functional existence of cerebral connections in adults and children. An image-guided TMS navigator will be used for accurate brain and cerebellum stimulation. Active vs. passive conditions of wrist movements or illusion of wrist movements induced by muscle vibration will be tested. Results may have a potential impact in neuro-rehabilitation to provide new guidelines for promoting hand distal function in patients with stroke and in very preterm children living with muscle coordination impairments.