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Hum Brain Mapp. 2014 Jul;35(7):3025-35. doi: 10.1002/hbm.22382. Epub 2013 Oct 18.

Dynamic causal modeling of load-dependent modulation of effective connectivity within the verbal working memory network.

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Department of Psychiatry, Icahn School of Medicine at Mount Sinai, New York, New York; Institute of Psychiatry, King's College London, London, United Kingdom.


Neuroimaging studies have consistently shown that working memory (WM) tasks engage a distributed neural network that primarily includes the dorsolateral prefrontal cortex, the parietal cortex, and the anterior cingulate cortex. The current challenge is to provide a mechanistic account of the changes observed in regional activity. To achieve this, we characterized neuroplastic responses in effective connectivity between these regions at increasing WM loads using dynamic causal modeling of functional magnetic resonance imaging data obtained from healthy individuals during a verbal n-back task. Our data demonstrate that increasing memory load was associated with (a) right-hemisphere dominance, (b) increasing forward (i.e., posterior to anterior) effective connectivity within the WM network, and (c) reduction in individual variability in WM network architecture resulting in the right-hemisphere forward model reaching an exceedance probability of 99% in the most demanding condition. Our results provide direct empirical support that task difficulty, in our case WM load, is a significant moderator of short-term plasticity, complementing existing theories of task-related reduction in variability in neural networks.


anterior cingulate; dorsolateral prefrontal cortex; fMRI; n-back task; neuroimaging; parietal; short-term plasticity

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