Dissociable roles of prefrontal subregions in self-ordered working memory performance.

The anatomical segregation of executive control processes within the prefrontal cortex remains poorly defined. The present study focused on strategy implementation on two working memory tasks: the CANTAB spatial working memory task and a visuospatial sequence generation task. These measures were administered to a group of frontal lesion patients and a comparison group of healthy subjects. Frontal patients with damage to the right inferior frontal gyrus were impaired on the CANTAB spatial working memory task, compared with healthy controls and patients without damage to this region. This deficit was most strongly related to the pars opercularis subregion (BA44) and was accompanied by poor strategy usage. On the sequence generation task, frontal lesion patients were impaired on a strategy-training phase when the working memory demands of the task were reduced, but had relatively intact performance on other phases of the task. Performance on the training phase was correlated with the amount of damage to the dorsolateral prefrontal cortex (DLPFC: BA46/9). These results support theoretical notions of prefrontal cortical function that emphasise its contribution to executive processes such as mnemonic strategies and monitoring over its role as a short-term memory store. Moreover, we provide evidence for the first time that such functions are dependent on dissociable brain regions within the prefrontal cortex.