VISUOSPATIAL MNEMONIC LOAD MODULATES EVENT-RELATED SLOW POTENTIALS

ELECTROENCEPHALOGRAPHIC slow wave potentials were recorded during the performance of visuospatial working memory tasks. The aim was to study the effects of varying mnemonic loads on slow potentials, and to diss ociate the contribution of mnemonic and motor components. Subjects wer e tested with three spatial delayed matching-to-sample tasks in which the mnemonic load varied while the preparatory motor demands remained constant. The delay-related slow potential was more negative during th e tasks in which the subjects had to memorize the locations of six or four stimuli than when only one location had to be memorized. Signific ant differences between the slow potentials in the tasks with differen t mnemonic loads were recorded at frontal and temporal recording sites . Since the preparatory motor requirements were similar in all tasks, the modulation of slow potentials reflects working memory processing r ather than motor preparatory activity.