A SPATIAL OCULOMOTOR MEMORY-TASK PERFORMANCE PRODUCES A TASK-RELATED SLOW SHIFT IN HUMAN ELECTROENCEPHALOGRAPHY

Electroencephalographic (EEG) deflections in humans related to the per formance of memory-guided saccades were studied in this work. The EEG deflections were recorded during 2 spatial oculomotor delayed response tasks in which the subject was instructed to make a saccade either to the right or to the left depending on the spatial location of the cue which had been shown in the beginning of the delay period. The EEG de flections were compared to those recorded during a control task in whi ch the subject also made a saccade to the right or to the left after a delay but the requirement to keep spatial information actively in min d was minimized. A slow delay-related shift was recorded during all ta sk conditions. The slow shift was positive in the most frontal and neg ative in the more posterior recording sites. The negative slow shift i n the more posterior recording sites was larger in the memory tasks th an in the control task. Since the memory and the control tasks differe d mainly in their requirement to hold spatial information in mind it i s suggested that the difference in the magnitude of slow shifts betwee n the memory and the control tasks reflects neural activity related to spatial working memory. But although the oculomotor responses in all tasks were similar, the preparatory activities for the impending eye m ovements may not have been similar and in addition to working memory m ay have contributed to the observed differences in the slow shifts.