CNV and EMG preceding a plantar flexion of the foot.

In 25 subjects CNV and EMG were recorded during a reaction time experiment with a fixed 4 sec foreperiod. The response was plantar flexion of the right foot. EEGs were recorded with four electrodes from the central area, two over each hemisphere. CNV amplitudes were larger over the ipsilateral than over the contralateral hemisphere. Amplitudes were smaller in the more lateral derivations. The late component of the CNV showed larger amplitudes when preceding relatively fast responses. EMG activity was recorded from the calf muscles of both legs. In the left leg it was not different during the intertrial interval and the foreperiod. A small but systematic increase in EMG activity was found during the foreperiod in the right leg. The increase was larger preceding fast responses, parallel to the amplitude changes in CNV late waves.