Scalp recorded slow potential shifts during isometric ramp and hold contractions in human subjects.

During voluntary isometric slow ramp contractions of the hand up to an internally defined target force level sustained negative potential shifts in the EEG were recorded from 6 human subjects. The potential shifts are composed of (a) a bilateral wide spread negativity with a maximum amplitude at the vertex, and (b) a smaller negative wave contralateral to the responding hand with a maximum over the respective motor area. Both components disappear during a voluntary isometric isotonic contraction when subjects have to maintain a stable force level for some seconds.