G. Mccarthy et al., FUNCTIONAL MAGNETIC-RESONANCE-IMAGING OF HUMAN PREFRONTAL CORTEX ACTIVATION DURING A SPATIAL WORKING-MEMORY TASK, Proceedings of the National Academy of Sciences of the United Statesof America, 91(18), 1994, pp. 8690-8694
High-speed magnetic resonance (MR) imaging was used to detect activati
on in the human prefrontal cortex induced by a spatial working memory
task modeled on those used to elucidate neuronal circuits in nonhuman
primates. Subjects were required to judge whether the location occupie
d by the current stimulus had been occupied previously over a sequence
of 14 or 15 stimuli presented in various locations. Control tasks wer
e similar in all essential respects, except that the subject's task wa
s to detect when one of the stimuli presented was colored red (color d
etection) or when a dot briefly appeared within the stimulus (dot dete
ction). In all tasks, two to three target events occurred randomly. Th
e MR signal increased in an area of the middle frontal gyrus correspon
ding to Brodmann's area 46 in all eight subjects performing the spatia
l working memory task. Right hemisphere activation was greater and mor
e consistent than left. The MR signal change occurred within 6-9 sec o
f task onset and declined within a similar period after task completio
n. An increase in MR signal was also noted in the control tasks, but t
he magnitude of change was less than that recorded in the working memo
ry task. These differences were replicated when testing was repeated i
n five of the original subjects. The localization of spatial working m
emory function in humans to a circumscribed area of the middle frontal
gyrus supports the compartmentalization of working memory functions i
n the human prefrontal cortex and the localization of spatial memory p
rocesses to comparable areas in humans and nonhuman primates.