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|Title:||RELATIVE CONTRIBUTION OF THE PARIETAL AND PREFRONTAL CORTEX IN WORKING MEMORY, AS DEMONSTRATED BY TRIAL-AVERAGED TIME-COURSES AND FUNCTIONAL CONNECTIVITY ANALYSES.|
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|Authors/Affiliations:||1 Anne Sophie Champod*; 1 Michael Petrides; |
1 Montreal Neurological Institute, Montreal, QC, Canada.
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|Content:||It is often reported in the literature that the parietal and prefrontal cortex constitute the neural network subserving working memory functions. However, to the best of our knowledge, no study has successfully dissociated the respective role of these brain regions in working memory processes. This event-related functional magnetic resonance imaging study tested the hypothesis that the mid-dorsolateral prefrontal cortex (MDLFC) is specifically related to the monitoring of information in working memory, whereas the intraparietal sulcus region (IPS) is additionally recruited when the information also has to be manipulated.|
Time-series and functional connectivity analyses were performed to compare brain activity throughout the performance of trials in which either manipulation, monitoring or simple recognition of information was required. Time-series analysis demonstrated that, within the IPS region, the signal increase related to the manipulation was occurring when the subjects were instructed to manipulate the presented abstract designs and was greater than the signal obtained during the monitoring and recognition of the same stimuli. Within the MDLFC region, the signal increase was occurring when the subjects were instructed to monitor the presented stimuli and was greater in the monitoring condition compared with the manipulation and control conditions. These results were consistent with the hypothesis of the role of the IPS and MDLFC regions in manipulation and monitoring processes, respectively. The functional connectivity analysis allowed us to determine how the two regions of interest (IPS and MDLFC) interacted with each other and with other cortical and subcortical structures during the performance of the manipulation and monitoring tasks. The results demonstrated that the broader functional circuit engaged in interaction with the regions of interest during the manipulation and monitoring of information was very similar. However, interestingly, functional connectivity in the task phases of the manipulation and monitoring trials when these were compared with each other, revealed that the IPS region interacted significantly more with the MDLFC during manipulation than during monitoring. This finding is consistent with the present hypothesis of the additional contribution of the IPS region in the manipulation of information in working memory. These results showed that the PPC is centrally involved in manipulation processes, while activation of the MDLFC is related to the monitoring of the information that is being manipulated. This study provides the first dissociation of activation in these two regions and, thus, succeeds in further specifying their relative contribution to working memory.
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