"What"-Then-Where" in visual working memory: an event-related fMRI study.
Behavioral studies indicate that spatial and object working memory are computed by dissociable subsystems. We investigated the neural bases of this dissociation with a whole-brain fMRI design and analysis technique that permitted direct assessment of delay-period activity, uncontaminated by other components of the trial. The task employed a "what"-then-"where" design, with an object and a spatial delay period incorporated in each trial; within-trial order of delay conditions was balanced across each scan. Our experiment failed to find evidence, at the single-subject level and at the group level, for anatomical segregation of spatial and object working memory function in the frontal cortex. Delay-period activity in the caudate nucleus revealed a sensitivity to position in the trial in the spatial, but not the object, condition. In posterior regions, spatial delay-period activity was associated with preferential recruitment of extrastriate areas falling within Brodmann's area 19 and, less reliably, the superior parietal lobule. Object-specific delay-period activity was found predominantly in ventral regions of the posterior cortex and demonstrated more topographic variability across subjects than did spatial working memory activity.
Postle
B R
BR
Department of Neurology, University of Pennsylvania Medical Center, 3 West Gates, Area 9,3400 Spruce St.,Philadelphia, PA 19104, USA. postle@mail.upenn.edu
D'Esposito
M
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D000328:Adult; D002421:Caudate Nucleus / Q000033:anatomy & histology / Q000502:physiology; D005260:Female; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008568:Memory / Q000502:physiology*; D009778:Occipital Lobe / Q000033:anatomy & histology / Q000503:physiopathology; D010296:Parietal Lobe / Q000033:anatomy & histology / Q000502:physiology; D017397:Prefrontal Cortex / Q000033:anatomy & histology / Q000502:physiology; D013702:Temporal Lobe / Q000033:anatomy & histology / Q000502:physiology; D014796:Visual Perception / Q000502:physiology*