Functional MRI studies of spatial and nonspatial working memory.
Single-unit recordings in monkeys have revealed neurons in the lateral prefrontal cortex that increase their firing during a delay between the presentation of information and its later use in behavior. Based on monkey lesion and neurophysiology studies, it has been proposed that a dorsal region of lateral prefrontal cortex is necessary for temporary storage of spatial information whereas a more ventral region is necessary for the maintenance of nonspatial information. Functional neuroimaging studies, however, have not clearly demonstrated such a division in humans. We present here an analysis of all reported human functional neuroimaging studies plotted onto a standardized brain. This analysis did not find evidence for a dorsal/ventral subdivision of prefrontal cortex depending on the type of material held in working memory, but a hemispheric organization was suggested (i.e., left-nonspatial; right-spatial). We also performed functional MRI studies in 16 normal subjects during two tasks designed to probe either nonspatial or spatial working memory, respectively. A group and subgroup analysis revealed similarly located activation in right middle frontal gyrus (Brodmann's area 46) in both spatial and nonspatial [working memory-control] subtractions. Based on another model of prefrontal organization [M. Petrides, Frontal lobes and behavior, Cur. Opin. Neurobiol., 4 (1994) 207-211], a reconsideration of the previous imaging literature data suggested that a dorsal/ventral subdivision of prefrontal cortex may depend upon the type of processing performed upon the information held in working memory.
D'Esposito
M
M
Department of Neurology, University of Pennsylvania Medical Center, Philadelphia, PA, USA despo@mail.med.upenn.edu
Aguirre
G K
GK
Zarahn
E
E
Ballard
D
D
Shin
R K
RK
Lease
J
J
D000328:Adult; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000502:physiology; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008570:Memory, Short-Term / Q000502:physiology*; D008959:Models, Neurological; D010364:Pattern Recognition, Visual / Q000502:physiology; D013028:Space Perception / Q000502:physiology; D014796:Visual Perception / Q000502:physiology