Opposite hemisphere differences in movement related potentials preceding foot and finger flexions.

Nine right-handed subjects performed an experiment in which the recording of the readiness potential (RP) and of the contingent negative variation (CNV) was combined. A microswitch was pressed by a voluntary foot or finger movement. 4 sec later a visual stimulus was presented, to which the subject had to respond as quickly as possible by making the same movement. Four electrode positions were used: C3, C4, C'3 and C'4, the latter two in between Cz and C3 or C4, respectively. The RPs showed larger amplitudes over the hemisphere, contralateral to the finger movement. Moreover, although not significant, RPs showed larger amplitudes over the hemisphere, ipsilateral to the foot movement. Late CNV waves were larger at C3 prior to a finger response and at C'4 prior to a foot response. This result is an argument for the hypothesis of a common underlying mechanism of RP and CNV late waves. Moreover, it suggests that motor preparation is a selective process which is related to the activation of a specific area in the motor cortex.