Prefrontal cortical representation of visuospatial working memory in monkeys examined by local inactivation with muscimol

In primates, dorsolateral areas of the prefrontal cortex (PFC) play a major role in visuospatial working memory. To examine the functional organizatio n of the PFC for representing visuospatial working memory, we produced reve rsible local inactivation, with the local injection of muscimol (5 mug, 1 m ul), at various sites (n = 100) in the dorsolateral PFC of monkeys and obse rved the behavioral consequences in an oculomotor delayed-response task tha t required memory-guided saccades for locations throughout both visual fiel ds. At 82 sites, the local injection of muscimol induced deficits in memory -guided saccades to a few specific, usually contralateral, target locations that varied with the location of the injection site. Such deficits depende d on the delay length, and longer delays were associated with larger defici ts in memory-guided saccades. The injection sites and affected spatial loca tions of the target showed a gross topographical relationship. No deficits appeared for a control task in which the subject was required to make a vis ually guided saccade to a visible target. These findings suggest that a spe cific site in the dorsolateral PFC is responsible for the working memory pr ocess for a specific visuospatial coordinate to guide goal-directed behavio r. Further, memoranda for specific visuospatial coordinates appear to be re presented in a topographical memory map within the dorsolateral PFC to repr esent visuospatial working memory processes.