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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.

Movements of the upper limb are well known to be preceded by electromyographic activity in leg and trunk muscles known as postural preadjustment. Brain potentials preceding the actual commencement of voluntary displacement were also described. The relationship between the occurrence of these two electrophysiological phenomena was investigated by performing two types of movement in three different body positions. Healthy subjects were free standing, sitting and standing with backsupport. When fast forward arm elevation was executed, the preceding Bereitschaftspotential was higher in amplitude at 500 msec before EMG onset and alongside midline scalp leads during sitting. The amplitude at 150 msec, immediately preceding movement, did not show significant differences related to body positions and there was no contralateral dominance. When index finger flexion was performed, it did not yield differences in the Bereitschaftspotential between sitting and standing positions. These findings suggest the existence of two separate stages of the preparatory process and an influence of the muscle mass involved in the stance perturbation during voluntary movement.

This study assessed the effects of training and ability to execute a voluntary movement upon movement-related brain potentials (MRBPs). A self-paced thumb flexion initiated a sequence of autotriggered electrical stimuli over the median nerve that caused a twitch opposing the intended thumb extension. The MRBPs had earlier onsets during the first runs of skill acquisition than during later training sessions; they occurred earlier when they preceded a stimulus train than when they preceded a single stimulus; the onset was earlier over the vertex than over the premotor area. MRBP duration was longer during train stimulation when a voluntary effort had to be maintained against tetanic contraction. MRBP amplitude did not reflect task requirements under these experimental conditions.

The task of the present study was the investigation of the brain potentials while performing a complex motor task, including voluntary sustained contraction (thumb opposition to the index finger). The fast press of a transducer was sustained for periods of 1.5, 5 or 10 seconds, followed by fast release. Potentials related to the start of the contraction were registered (Bereitschaftspotential, N2, etc.) with considerable interindividual variability. The end of the contraction was preceded, too, by a slow potential, similar to Bereitschaftspotential, with prevailing positivity over frontal areas and negativity over postcentral areas; N2 at the release was well expressed, regardless of the polarity of the preceding slow potential. During the sustained contraction a steady positivity was registered. The presence of potentials related to the start as well as to the end of the voluntary effort suggests the existence of two separate commands. The positivity sustained throughout the contraction, strongly expressed frontally and decreasing postcentrally, implies a decisive role for central processes including the organization and preprogramming of the motor task, but not direct reflection of feedback kinaesthetic afferentation.

The presence of brain potentials related to the end of a sustained isometric contraction prompted this study. Potentials related to the beginning of simple ballistic flexion of the index finger were compared with isometric contraction, potentials related to the termination of the isometric contraction, and potentials related to ballistic extension of the reposed index finger. The electroencephalograms recorded in 10 healthy volunteers from scalp positions C3+2, Cz, C3-2 were averaged time-locked to the appropriate mechanograms. Both negativity preceding and positivity following execution of movement were better expressed with simple flexion movements. The negativities preceding all four types of movements were of comparable magnitude whilst the positivities differed significantly. These findings were considered as supporting the ideas of general facilitation preceding preparation for action and specific feedback information following execution, the changes being more prominent over postcentral leads. The existence of potentials related to the termination of voluntary sustained isometric contraction implied a separate command for antagonistic muscles.