Brain macropotentials associated with distinct phases of voluntary sustained isometric contraction in man

Brain potentials recorded from the scalp during voluntary sustained isometric contraction have been consistently found to accompany both the beginning and the termination of the contraction. This study attempts to evaluate the dependence of the potentials related to the voluntary termination of a sustained effort on the physical parameters of the motor task and also to further investigate the relationship between potentials related to the initiation and to the termination of action. Brain potentials from healthy male volunteers performing hand-grip squeeze were time-locked to (1) beginning of contraction; (2) execution of an additional effort; and (3) the moment of voluntary relaxation, and then averaged. The waveshape and amplitude of the entire potential curve preceding and following the decision to act were evaluated with best-fit mathematical approximation procedures. Few correlations between the various descriptive parameters of the three types of potentials were found. The brain potentials accompanying beginning of the contraction from state of rest differed significantly from those accompanying execution of an additional effort and both potentials preceding initiation of voluntary effort differed from potentials preceding decision to terminate the action. It is hypothesised that brain macropotentials are linked to separate underlying commands for initiation and termination of voluntary action.