The roles of prefrontal brain regions in components of working memory: Effects of memory load and individual differences

Using an event-related functional MRI design, we explored the relative role s of dorsal and ventral prefrontal cortex (PFC) regions during specific com ponents (Encoding, Delay, Response) of a working memory task under differen t memory-load conditions. In a group analysis, effects of increased memory load were observed only in dorsal PFC in the encoding period. Activity was lateralized to the right hemisphere in the high but not the low memory-load condition. Individual analyses revealed variability in activation patterns across subjects. Regression analyses indicated that one source of variabil ity was subjects' memory retrieval rate. It was observed that dorsal PFC pl ays a differentially greater role in information retrieval for slower subje cts, possibly because of inefficient retrieval processes or a reduced quali ty of mnemonic representations. This study supports the idea that dorsal an d ventral PFC play different roles in component processes of working memory .