Movement-related cortical potentials associated with voluntary relaxation of foot muscles

Objective: In our previous study of movement-related cortical potential (MRCP) in association with the voluntary relaxation of the hand muscle, Bereitschaftspotential (BP) was maximal at the vertex and symmetrically distributed, and Negative Slope (NS′) was maximal over the contralateral central region. In order to clarify the generator sources of MRCP with voluntary muscle relaxation, we recorded MRCP in association with voluntary relaxation of the foot. Methods: MRCP in association with plantar flexion of the foot caused by voluntary relaxation of the tibialis anterior muscle was recorded in 10 normal subjects. Results: The BP started at about 1.7 s before the onset of the muscle relaxation, followed by NS′ starting at about 650 ms before it. Both were maximal at the vertex and symmetrically distributed. There was no additional EEG activity in the lateral frontal areas, which are presumably located over the primary negative motor areas (PNMA). Conclusions: It is concluded that the voluntary muscle relaxation, similarly to the voluntary muscle contraction, involves the cortical preparatory activity at least in the primary motor area (M1) and probably the supplementary motor areas (SMAs). There is no evidence to suggest that the PNMA is also active prior to the voluntary muscle relaxation.