Plasticity of motor cortex induced by coordination and training

To study the modifications induced by training of a coordinated movement on the primary motor cortex (M1) maps of one proximal muscle and one distal muscle activated alone and during their co-contraction.

Six healthy female sport students performed a 6-week training program during which they were trained in darts 3-4 times a week. At the end each subject had made more than 1200 throws. Transcranial magnetic stimulation (TMS) was used to map the proximal medial deltoid (MD) and the distal brachio-radialis (BR) muscle representations on M1. Motor evoked potentials (MEPs) amplitude and excitability curves were used to test corticomotor excitability.

The cortical representation areas of each muscle separately increased after training. The cortical representation and the excitability curve of the BR muscle increased during co-activation with the MD. Combining co-contraction and training produced a further enlargement of the M1 representation of the BR muscle.

The enlargement of the BR representation in M1 suggests the development of overlapping zones specifying functional synergies between distal and proximal muscles.

Our findings support the idea that training of a coordinated movement involving several muscles and joints requires an activity-dependent coupling of cortical networks.