Distinguishing the functional roles of multiple regions in distributed neural systems for visual working memory

We have investigated the human neural systems for visual working memory usi ng functional magnetic resonance imaging to distinguish sustained activity during memory delays from transient responses related to perceptual and mot or operations. These studies have identified six distinct frontal regions t hat demonstrate sustained activity during memory delays. These regions coul d be distinguished from brain regions in extrastriate cortex that participa te more in perception and from brain regions in medial and lateral frontal cortex that participate more in motor control. Moreover, the working memory regions could be distinguished from each other based on the relative stren gth of their participation in spatial and face working memory and on the re lative strength of sustained activity during memory delays versus transient activity related to stimulus presentation. These results demonstrate that visual working memory performance involves the concerted activity of multip le regions in a widely distributed system. Distinctions between functions, such as perception versus memory maintenance, or spatial versus face workin g memory, are a matter of the degree of participation of different regions, not the discrete parcellation of different functions to different modules. (C) 2000 Academic Press.