Article

Functional magnetic-resonance-imaging of human prefrontal cortex activation during a spatial working-memory task

Neuropsychology Laboratory, Veterans Affairs Medical Center, West Haven, CT 06516.
Proceedings of the National Academy of Sciences (Impact Factor: 9.81). 09/1994; 91(18):8690-4. DOI: 10.1073/pnas.91.18.8690
Source: PubMed

ABSTRACT High-speed magnetic resonance (MR) imaging was used to detect activation 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 occupied by the current stimulus had been occupied previously over a sequence of 14 or 15 stimuli presented in various locations. Control tasks were similar in all essential respects, except that the subject's task was to detect when one of the stimuli presented was colored red (color detection) or when a dot briefly appeared within the stimulus (dot detection). In all tasks, two to three target events occurred randomly. The MR signal increased in an area of the middle frontal gyrus corresponding to Brodmann's area 46 in all eight subjects performing the spatial working memory task. Right hemisphere activation was greater and more consistent than left. The MR signal change occurred within 6-9 sec of task onset and declined within a similar period after task completion. An increase in MR signal was also noted in the control tasks, but the magnitude of change was less than that recorded in the working memory task. These differences were replicated when testing was repeated in five of the original subjects. The localization of spatial working memory function in humans to a circumscribed area of the middle frontal gyrus supports the compartmentalization of working memory functions in the human prefrontal cortex and the localization of spatial memory processes to comparable areas in humans and nonhuman primates.

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    • "Funahashi et al. (1989) demonstrated that neurons in the prefrontal cortex emit stimulus-specific sustained discharge during the delay period in the WM paradigm. In humans, functional magnetic resonance imaging (fMRI) studies, which measure the hemodynamic change resulting from neuronal activation, support the role of prefrontal regions in WM (McCarthy et al. 1994, 1996; D'Esposito 2007). "
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    • "In general, relational integration relies only in part on the executive resources of working memory (Cho et al., 2007; Badre, 2008) and attention (Posner and Petersen, 1990). Previous experiments have shown that reasoning involves, but is separate from working memory (McCarthy et al., 1994; Owen et al., 1996; Bechara et al., 1998; Ruff et al., 2003; Cowan et al., 2012). In fact, functional nuclei are distributed throughout the human frontal lobes that enable diverse executive functions (Duncan and Owen, 2000), though they appear uniform to the human eye. "
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    • "Several functional magnetic resonance imaging (fMRI) studies published toward the end of 20th century focused primarily on identifying a domain-based segregation of working memory within the prefrontal cortex for objects and locations (Courtney et al., 1996, 1997, 1998; McCarthy et al., 1996; Belger et al., 1998; Kelley et al., 1998; Smith and Jonides, 1999). However, other fMRI studies, also published during this time, reported results contradictory to domain-based segregation (McCarthy et al., 1994; D&apos;Esposito et al., 1998a; Owen et al., 1998; Petit et al., 1998; Postle and D'Esposito, 1999a,b). In the period that followed, investigators began shifting their focus to other brain regions in an attempt to elucidate what domain-specificity (object vs. location ) might exist within working memory. "
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