Effective connectivity during working memory and resting states: A DCM study

Although the relationship between resting-state functional connectivity and task-related activity has been addressed, the relationship between task and resting-state directed or effective connectivity - and its behavioral concomitants - remains elusive. We evaluated effective connectivity under an N-back working memory task in 24 participants using stochastic dynamic causal modelling (DCM) of 7 T fMRI data. We repeated the analysis using resting-state data, from the same subjects, to model connectivity among the same brain regions engaged by the N-back task. This allowed us to: (i) examine the relationship between intrinsic (task-independent) effective connectivity during resting (A(rest)) and task states (A(task)), (ii) cluster phenotypes of task-related changes in effective connectivity (B-task) across participants, (iii) identify edges (B-task) showing high inter-individual effective connectivity differences and (iv) associate reaction times with the similarity between B-task and A(rest) in these edges. We found a strong correlation between A(rest) and A(task) over subjects but a marked difference between B-task and A(rest). We further observed a strong clustering of individuals in terms of B-task, which was not apparent in A(rest). The task-related effective connectivity B-task varied highly in the edges from the parietal to the frontal lobes across individuals, so the three groups were clustered mainly by the effective connectivity within these networks. The similarity between B-task and A(rest) at the edges from the parietal to the frontal lobes was positively correlated with 2-back reaction times. This result implies that a greater change in context-sensitive coupling - from resting-state connectivity - is associated with faster reaction times. In summary, task-dependent connectivity endows resting-state connectivity with a context sensitivity, which predicts the speed of information processing during the N-back task.