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Working memory load modulation of parieto-frontal connections: evidence from dynamic causal modeling.

ABSTRACT: Previous neuroimaging studies have shown that working memory load has marked effects on regional neural activation. However, the mechanism through which working memory load modulates brain connectivity is still unclear. In this study, this issue was addressed using dynamic causal modeling (DCM) based on functional magnetic resonance imaging (fMRI) data. Eighteen normal healthy subjects were scanned while they performed a working memory task with variable memory load, as parameterized by two levels of memory delay and three levels of digit load (number of digits presented in each visual stimulus). Eight regions of interest, i.e., bilateral middle frontal gyrus (MFG), anterior cingulate cortex (ACC), inferior frontal cortex (IFC), and posterior parietal cortex (PPC), were chosen for DCM analyses. Analysis of the behavioral data during the fMRI scan revealed that accuracy decreased as digit load increased. Bayesian inference on model structure indicated that a bilinear DCM in which memory delay was the driving input to bilateral PPC and in which digit load modulated several parieto-frontal connections was the optimal model. Analysis of model parameters showed that higher digit load enhanced connection from L PPC to L IFC, and lower digit load inhibited connection from R PPC to L ACC. These findings suggest that working memory load modulates brain connectivity in a parieto-frontal network, and may reflect altered neuronal processes, e.g., information processing or error monitoring, with the change in working memory load. Hum Brain Mapp, 2012. © 2011 Wiley Periodicals, Inc.

SUBMITTER: Ma L

PROVIDER: S-EPMC3179779 | biostudies-literature | 2012 Aug

REPOSITORIES: biostudies-literature

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Working memory load modulation of parieto-frontal connections: evidence from dynamic causal modeling.

Ma Liangsuo L Steinberg Joel L JL Hasan Khader M KM Narayana Ponnada A PA Kramer Larry A LA Moeller F Gerard FG

Human brain mapping 20110620 8

Previous neuroimaging studies have shown that working memory load has marked effects on regional neural activation. However, the mechanism through which working memory load modulates brain connectivity is still unclear. In this study, this issue was addressed using dynamic causal modeling (DCM) based on functional magnetic resonance imaging (fMRI) data. Eighteen normal healthy subjects were scanned while they performed a working memory task with variable memory load, as parameterized by two leve ...[more]

PMID: 21692148

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Project description:Many neuroimaging studies have demonstrated the different functional contributions of spatially distinct brain areas to working memory (WM) subsystems in cognitive tasks that demand both local information processing and interregional coordination. In WM cognitive task paradigms employing electroencephalography (EEG), brain rhythms such as ? and ? have been linked to specific functional roles over given brain areas, but their functional coupling has not been extensively studied. Here we analyzed an arithmetic task with five cognitive workload levels (CWLs) and demonstrated functional/effective coupling between the two WM subsystems: the central executive located over frontal (F) brain areas that oscillates on the dominant ? rhythm (Frontal(?)/F(?)) and the storage buffer located over parieto-occipital (PO) brain areas that operates on the ?2 dominant brain rhythm (Parieto-Occipital(?2)/PO(?2)). We focused on important differences between and within WM subsystems in relation to behavioral performance. A repertoire of brain connectivity estimators was employed to elucidate the distinct roles of amplitude, phase within and between frequencies, and the hierarchical role of functionally specialized brain areas related to the task. Specifically, for each CWL, we conducted a) a conventional signal power analysis within both frequency bands at F(?) and PO(?2), b) the intra- and inter-frequency phase interactions between F(?) and PO(?2), and c) their causal phase and amplitude relationship. We found no significant statistical difference of signal power or phase interactions between correct and wrong answers. Interestingly, the study of causal interactions between F(?) and PO(?2) revealed frontal brain region(s) as the leader, while the strength differentiated between correct and wrong responses in every CWL with absolute accuracy. Additionally, zero time-lag between bilateral F(?) and right PO(a2) could serve as an indicator of mental calculation failure. Overall, our study highlights the significant role of coordinated activity between F(?) and PO(?2) via their causal interactions and the timing for arithmetic performance.

Dataset Information

Working memory load modulation of parieto-frontal connections: evidence from dynamic causal modeling.

Publications

Working memory load modulation of parieto-frontal connections: evidence from dynamic causal modeling.

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