Reorganization of frontal systems used by alcoholics for spatial working memory: An fMRI study

Chronic alcoholism is associated with impairment in sustained attention and visual working memory. Thus, alcoholics have reduced ability, but not nece ssarily inability, to perform these executive tasks, assumed to be subserve d by regions of prefrontal cortex. To identify neural substrates associated with this impairment, we used functional MRI (fMRI) to determine whether a lcoholics invoke the same or different brain systems as controls when engag ed in working memory tasks that the two groups were able to perform at equi valent levels. The fMRI spatial working memory paradigm instructed subjects to respond with a button press when a target position was either in the ce nter of the field (match to center) or matched the spatial position of one presented two items previously (match 2-back) or to rest. Using whole-brain fMRI, alcoholics showed diminished activation frontal cortical systems com pared to controls (bilateral dorsolateral prefrontal cortex) when respondin g a-back vs rest. In the center vs rest contrast, the control group compare d with the alcoholic group activated a large expanse of prefrontal cortex ( including Brodmann areas 9, 10, and 45), whereas there was significantly gr eater activation by the alcoholic group relative to the control group local ized more posteriorly and inferiorly in the frontal cortex (area 47). Exami nation of within group activation patterns revealed two different patterns of activation: the control group exhibited activation of the dorsal ("Where ?") stream for visual spatial working memory processing, whereas the alcoho lic group exhibited activation of the ventral ("What?") stream and declarat ive memory systems to accomplish the spatial working memory task. The diffe rences in the pattern of brain activations exhibited by the alcoholic and c ontrol groups, despite equivalence in behavioral performance, is consistent with a functional reorganization of the brain systems invoked by alcoholic individuals or invocation of an inappropriate brain system when engaged in a visual spatial task requiring working memory. (C) 2001 Academic Press.