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Functional MRI studies of spatial and nonspatial working memory
M D'Esposito1, G K Aguirre, E Zarahn
1Department of Neurology, University of Pennsylvania Medical Center, Philadelphia, PA, USA despo@mail.med.upenn.edu
Brain Research. Cognitive Brain Research
|August 26, 1998
Summary
Human brain imaging studies suggest working memory functions are organized by hemisphere, not dorsal/ventral regions. Spatial information may be processed in the right hemisphere, and nonspatial in the left.
Area of Science:
- Neuroscience
- Cognitive Neuroscience
- Neuroimaging
Background:
- Previous research in monkeys suggested distinct dorsal and ventral regions of the lateral prefrontal cortex for spatial and nonspatial working memory, respectively.
- Human functional neuroimaging studies have not consistently supported this dorsal/ventral subdivision based on information type.
- Alternative models propose prefrontal cortex organization based on processing type rather than information content.
Purpose of the Study:
- To investigate the organization of spatial and nonspatial working memory within the human prefrontal cortex.
- To reconcile conflicting findings from monkey studies and human neuroimaging regarding prefrontal cortex function in working memory.
- To explore potential hemispheric or dorsal/ventral subdivisions within the lateral prefrontal cortex for working memory tasks.
Main Methods:
- Meta-analysis of all reported human functional neuroimaging studies on working memory, plotted onto a standardized brain.
- Functional magnetic resonance imaging (fMRI) in 16 healthy subjects performing spatial and nonspatial working memory tasks.
- Group and subgroup analyses of fMRI data to identify brain activation patterns.
Main Results:
- Meta-analysis did not support a dorsal/ventral subdivision based on material type but suggested a hemispheric organization (left-nonspatial, right-spatial).
- fMRI studies revealed similar activation in the right middle frontal gyrus (Brodmann's area 46) for both spatial and nonspatial working memory tasks.
- Reconsideration of literature, based on an alternative model, suggests a dorsal/ventral division might relate to the type of processing.
Conclusions:
- The human lateral prefrontal cortex may exhibit a hemispheric, rather than a dorsal/ventral, organization for spatial versus nonspatial working memory.
- Activation in the right middle frontal gyrus is involved in both spatial and nonspatial working memory maintenance.
- The functional organization of the prefrontal cortex in working memory might be better understood by considering the nature of cognitive operations performed.