A. Pfefferbaum et al., Reorganization of frontal systems used by alcoholics for spatial working memory: An fMRI study, NEUROIMAGE, 14(1), 2001, pp. 7-20
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.