A spatial oculomotor memory-task performance produces a task-related slow shift in human electroencephalography

Electroencephalographic (EEG) deflections in humans related to the performance 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 deflections were compared to those recorded during a control task in which 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 mind was minimized. A slow delay-related shift was recorded during all task conditions. The slow shift was positive in the most frontal and negative in the more posterior recording sites. The negative slow shift in the more posterior recording sites was larger in the memory tasks than in the control task. Since the memory and the control tasks differed mainly in their requirement to hold spatial information in mind it is suggested that the difference in the magnitude of slow shifts between 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 movements may not have been similar and in addition to working memory may have contributed to the observed differences in the slow shifts.