Authors:

OWEN, A.M., Lee, A.C.H. & Williams,

Reference:

Year of publication:

2000

CBU number:

4007

Abstract:

Evidence is now converging to suggests that working memory processes within the dorsolateral and ventrolateral frontal cortices are organised according to the type of processing required, rather than according to the nature (i.e. domain), of the information being processed, as has been widely assumed. For example, recent PET studies have demonstrated that either, or both, of these two lateral frontal areas can be activated in spatial working memory tasks, depending on the precise executive processes that are called upon by the task being performed. Moreover, in a recent study using fMRI, performance of visual spatial and visual non-spatial working memory tasks was shown to involve identical regions of the lateral prefrontal cortex when all factors unrelated to the type of stimulus domain were appropriately controlled. These results concur fully with recent reviews of the imaging literature, which have demonstrated that spatial and non-spatial working memory studies in general, have produced a widely distributed pattern of overlapping activation foci within these lateral frontal regions. In this study, the effects of varying the executive requirements of a simple verbal working memory task (forward versus backward digit span), were explored in eight subjects using positron emission tomography, in order to establish whether this model generalises to the verbal domain. As expected, during forward digit span, significant activation was observed within the mid-ventrolateral frontal cortex, but not within the mid-dorsolateral frontal cortex. In contrast, during backward digit span significant activation was observed in both regions. The results provide further evidence that the mid-dorsolateral and mid-ventrolateral frontal cortical areas make distinct functional contributions to memory and correspond with a fractionation of working memory processes in psychological terms.