Control regions in the brain are thought to provide signals that configure the brain's moment-to-moment information processing. Previously, we identified regions that carried signals related to taskcontrol initiation, maintenance, and adjustment. Here we characterize the interactions of these regions by applying graph theory to resting state functional connectivity MRI data. In contrast to previous, more unitary models of control, this approach suggests the presence of two distinct task-control networks. A frontoparietal network included the dorsolateral prefrontal cortex and intraparietal sulcus. This network emphasized start-cue and error-related activity and may initiate and adapt control on a trial-by-trial basis. The second network included dorsal anterior cingulate/medial superior frontal cortex, anterior insula/frontal operculum, and anterior prefrontal cortex. Among other signals, these regions showed activity sustained across the entire task epoch, suggesting that this network may control goaldirected behavior through the stable maintenance of task sets. These two independent networks appear to operate on different time scales and affect downstream processing via dissociable mechanisms.attention ͉ connectivity ͉ executive control ͉ functional MRI ͉ task set H umans possess unrivaled cognitive flexibility. When performing goal-directed tasks, humans are thought to adopt task sets that flexibly configure information processing in response to changing task demands. The brain's task-control system is thought to consist of functionally diverse regions that are anatomically separate from downstream processing systems (1).Previously, we studied mixed blocked/event-related fMRI data across a wide range of tasks (2). Because mixed fMRI designs can disambiguate sustained set-maintenance activity from more transient set and trial-related activity (3, 4), we were able to identify regions that carried three different putative task-control signals: (i) activity time-locked to the beginning of task periods (control initiation), (ii) set-maintenance signals sustained across the entire task period, and (iii) error-related activity (for feedback and control adjustment). Using cross-studies analyses, we identified a collection of regions thought to support these various task-control signals.The dorsal anterior cingulate cortex/medial superior frontal cortex (dACC/msFC) and bilateral anterior insula/frontal operculum (aI/fO) were the only regions that showed all three task-control signals (set initiation, maintenance, and feedback and adjustment) across a wide range of tasks. Therefore, we proposed that the dACC/msFC and aI/fO might

Prior LJ, Nolan TS, Snyder AZ, Raichle ME. Morning-evening variation in human brain metabolism and memory circuits. J Neurophysiol 109: 1444 -1456, 2013. First published November 28, 2012 doi:10.1152/jn.00651.2012.-It has been posited that a critical function of sleep is synaptic renormalization following a net increase in synaptic strength during wake. We hypothesized that wake would alter the resting-state functional organization of the brain and increase its metabolic cost. To test these hypotheses, two experiments were performed. In one, we obtained morning and evening resting-state functional MRI scans to assess changes in functional brain organization. In the second experiment, we obtained quantitative positron emission tomography measures of glucose and oxygen consumption to assess the cost of wake. We found selective changes in brain organization. Most prominently, bilateral medial temporal regions were locally connected in the morning but in the evening exhibited strong correlations with frontal and parietal brain regions involved in memory retrieval. We speculate that these changes may reflect aspects of memory consolidation recurring on a daily basis. Surprisingly, these changes in brain organization occurred without increases in brain metabolism.

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