FUNCTIONAL MAGNETIC-RESONANCE-IMAGING OF HUMAN PREFRONTAL CORTEX ACTIVATION DURING A SPATIAL WORKING-MEMORY TASK

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.