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Lateral prefrontal cortex activity may be modulated by the configuration of stimuli in a spatial working memory task
Society for Neuroscience Abstracts, 26, 1501
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Recent studies have attempted to dissociate regions within the lateral prefrontal cortex (PFC) by comparing "simple" working memory (WM) tasks, where there is an isomorphism between stimulus input and output, with more complex tasks that involve the "manipulation" or "monitoring" of the stimulus input in order to make a "transformed" response. However, these tasks differ in many ways, any one of which may contribute to the differences in activation patterns observed. To address this problem, we used PET to compare two versions of a spatial span task that differed only in terms of the spatial locations of the stimuli. In one version of the task, the stimuli were presented in random locations, while in the other an ordered 2 by 4 matrix was presented. When the "random array" 5 span task was compared to a ("1-span") control, significant changes were observed in the right ventrolateral PFC (VPFC), replicating two published studies that also used a "random array" 5 span task. In contrast, during the "ordered array" 5 span task, significant activation was observed in both the right dorsolateral PFC (DLPFC) and VPFC, when compared to the control. These findings indicate that subtle changes in the configuration of WM tasks may be sufficient to dissociate regions within the lateral PFC. The results of a follow-up behavioural study indicated that the ordered array span condition may facilitate mnemonic strategies, thus providing a plausible functional basis for the observed activation within the DLPFC. Preliminary evidence from a group of patients with damage to the lateral PFC lends further support to this suggestion.