Cerebral Cortex Advance Access published online on November 13, 2007
Cerebral Cortex, doi:10.1093/cercor/bhm195
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Dynamic Adjustments in Prefrontal, Hippocampal, and Inferior Temporal Interactions with Increasing Visual Working Memory Load
1 Henry H. Wheeler, Jr. Brain Imaging Center, University of California-Berkeley, Berkeley, CA 94720, USA, 2 Department of Psychology, University of California-Berkeley, Berkeley, CA 94720, USA, 3 Helen Wills Neuroscience Institute, University of California-Berkeley, Berkeley, CA 94720, USA, 4 Current address: Departments of Neurology and Physiology, University of California-San Francisco, San Francisco, CA 94158, USA
Address correspondence to Jesse Rissman, Department of Psychology, Stanford University, Jordan Hall, Building 420, Stanford, CA 94305-2130, USA. Email: jesse.rissman{at}stanford.edu.
The maintenance of visual stimuli across a delay interval in working memory tasks is thought to involve reverberant neural communication between the prefrontal cortex and posterior visual association areas. Recent studies suggest that the hippocampus might also contribute to this retention process, presumably via reciprocal interactions with visual regions. To characterize the nature of these interactions, we performed functional connectivity analysis on an event-related functional magnetic resonance imaging data set in which participants performed a delayed face recognition task. As the number of faces that participants were required to remember was parametrically increased, the right inferior frontal gyrus (IFG) showed a linearly decreasing degree of functional connectivity with the fusiform face area (FFA) during the delay period. In contrast, the hippocampus linearly increased its delay period connectivity with both the FFA and the IFG as the mnemonic load increased. Moreover, the degree to which participants' FFA showed a load-dependent increase in its connectivity with the hippocampus predicted the degree to which its connectivity with the IFG decreased with load. Thus, these neural circuits may dynamically trade off to accommodate the particular mnemonic demands of the task, with IFG–FFA interactions mediating maintenance at lower loads and hippocampal interactions supporting retention at higher loads.
Key Words: beta series correlation analysis • fMRI • functional connectivity • medial temporal lobe • short-term memory
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