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Measuring and Manipulating Functionally Specific Neural Pathways in the Human Motor System with Transcranial Magnetic Stimulation
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Interhemispheric interactions between trunk muscle representations of the primary motor cortex.
Loyda Jean-Charles1,2, Jean-Francois Nepveu1,2, Joan E Deffeyes1,2
1Département de Neurosciences, Faculté de Médecine, Université de Montréal, Montreal, Quebec, Canada.
Journal of Neurophysiology
|June 16, 2017
Summary
Unilateral arm movements rely on trunk stabilization via axial muscles. This study reveals that interhemispheric inhibition is key for trunk muscles during such tasks, with facilitation occurring via other pathways.
Area of Science:
- Neuroscience
- Motor Control
- Human Physiology
Background:
- Unilateral arm movements necessitate trunk stabilization through bilateral contraction of axial muscles.
- The precise interhemispheric interactions between primary motor cortices (M1) enabling coordinated trunk muscle contractions remain largely unknown.
- Understanding these mechanisms is crucial for explaining motor control during complex tasks.
Purpose of the Study:
- To investigate interhemispheric interactions within the primary motor cortex (M1) related to trunk-stabilizing muscles.
- To compare these interactions with those of agonist arm muscles during a unilateral motor task.
- To elucidate the neural pathways involved in coordinating axial muscles during arm movements.
Main Methods:
- Transcranial magnetic stimulation (TMS) was used to probe M1 excitability.
- Ipsilateral silent periods (iSP) and motor evoked potentials (iMEP) were recorded from erector spinae (ES L1), anterior deltoid (AD), and first dorsal interosseous (FDI) muscles.
- Dual-coil TMS and cervicomedullary stimulation were employed to differentiate intracortical, interhemispheric, and subcortical pathways.
Main Results:
- TMS elicited iSPs in all tested muscles; however, iMEPs, potentially indicating facilitation, were observed only in ES L1.
- Cervicomedullary stimulation suggested iSPs originate from intracortical mechanisms, while iMEPs involve other pathways.
- Interhemispheric inhibition was evident at specific intervals for both trunk and arm muscles, with differences suggesting task-dependent modulation.
Conclusions:
- Interhemispheric inhibition appears dominant for axial muscles during trunk stabilization tasks.
- Ipsilateral facilitation, possibly via subcortical or ipsilateral pathways, may be recruited depending on the axial muscles' role.
- These findings provide novel insights into the neural control of coordinated movements involving limb and trunk muscles.
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