Visuospatial mnemonic load modulates event-related slow potentials

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Abstract
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 dissociate the contribution of mnemonic and motor components. Subjects were 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 the tasks in which the subjects had to memorize the locations of six or four stimuli than when only one location had to be memorized. Significant differences between the slow potentials in the tasks with different 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 rather than motor preparatory activity.