Cerebral events preceding self-paced and visually triggered saccades. A study of presaccadic potentials

The cerebral potentials preceding self-paced and visually triggered saccadic eye movements were studied using multichannel recording and spatio-temporal mapping techniques, and the contribution to these potentials of stimulus-evoked activity and the electro-oculographic field was investigated. A premotor positivity (PMP) and negativity (PMN) comparable to those associated with movements of the extremities were found with both self-paced and triggered saccades, but there were differences in the amplitude, duration and topography of these potentials in the different types of eye movement. The slope of the PMP was greater for visually triggered than for self-paced saccades and its slope and duration were influenced by the predictability of the triggering stimulus, the slope being greater and the duration shorter with predictable than with unpredictable stimuli. The characteristics of this potential are compatible with an origin from saccade-related and visually sensitive neurons in parietal and occipital cortex and it is suggested that in a visually triggered eye movement, the PMP may be a correlate of visuomotor interactions. A PMN was associated with both self-paced and visually triggered saccades, and in the case of triggered saccades is thought to reflect anticipation of the cuing stimulus in addition to preparatory movement-related activity. When the precise timing of the cuing stimulus was not known by the subject, a PMN still developed but then plateaued until the arrival of the stimulus and execution of the movement. In this situation the PMN therefore appears to reflect an increasing level of arousal and preparedness to move which is then maintained pending the final motor command.