THE PRESACCADIC CORTICAL NEGATIVITY PRIOR TO SELF-PACED SACCADES WITHAND WITHOUT VISUAL GUIDANCE

The presaccadic negativity (PSN) of the scalp EEG potential prior to s elf-initiated saccades aimed either at a visual target or at the remem bered position of that target in total darkness was analysed in 10 nor mal subjects. Under both conditions a PSN with a negligible EOG contam ination was found, showing 4 characteristics: (1) In both conditions, the PSN maximum is localized at the vertex, probably containing the ac tivity of the supplementary motor area. (2) At an electrode placed ove r the frontal eye field (FEF) contralateral to the saccade direction. there is a temporary, circumscribed maximum prior to saccades to the v isual target, thus probably reflecting activity of the FEF. (3) Prior to saccades to the visual target, there is a statistically significant interhemispheric difference of the PSN over the parietal cortex with a larger amplitude over the hemisphere contralateral to the saccade di rection; this might be attributed to directed visual attention. (4) Pr ior to saccades without visual guidance in darkness there is a statist ically significant interhemispheric difference of the PSN over the fro ntal cortex with a larger amplitude over the hemisphere contralateral to the saccade direction. The amplitude of the PSN decreased in the co urse of the experiment: probably due to psychological factors such as attention and motivation. Our results suggest that the PSN is a readin ess potential preceding voluntary saccades, containing activity relate d both to unspecific psychological processes and to specific movement preparation in the frontal and parietal ocular motor areas.