Poster B49, Sunday, March 26, 8:00 – 10:00 am, Pacific Concourse
Interacting long-range networks govern control over working memory
Elizabeth L. Johnson1, Callum D. Dewar1,2, Anne-Kristin Solbakk3, Tor Endestad3, Torstein R. Meling3, Robert T. Knight1; 1University of California, Berkeley, 2University of Illinois, 3University of Oslo
We investigated how frontal regions exert control over sensory mechanisms in working memory (WM). The electroencephalogram (EEG) was recorded in 14 patients with unilateral lesions localized to lateral prefrontal cortex (LPFC; age 46 ± 16) and 20 age-matched controls while they completed a visual WM task. On each trial, subjects encoded two colored shapes in specific spatiotemporal positions in preparation for a subsequent test on the identity of each shape in the pair, or on the spatial or temporal relationship between the shapes in the pair. The test prompt was presented mid-delay to initiate executive control processes (processing period). Patients exhibited impaired accuracy (87% vs. 95%, p<0.00005 ), which indicates a causal but not unitary role for LPFC in WM. Processing was marked by anterior slow (1-8 Hz) power increases and anterior-to-posterior directional connectivity alongside central-posterior alpha-beta (8-20 Hz) power decreases and posterior-to-anterior connectivity (all p<0.001). Early in processing, we observed more hemispheric asymmetry, with decreased low theta (3-4 Hz) power at the lesion site, and less anterior-to-posterior connectivity in patients (all p<0.05, corrected). We then observed that LPFC lesions could be reliably identified from parieto-occipital alpha-beta power for the remaining processing period. These results reveal an LPFC source for theta rhythms underlying executive control, a dissociable alpha-beta suppression network for WM, and a cause-and-effect relationship between LPFC theta activity and parieto-occipital alpha-beta suppression. Our findings contradict modular views of LPFC in WM, and instead demonstrate that WM is governed by the flexible recruitment of bidirectional, interacting long-range networks.
Topic Area: EXECUTIVE PROCESSES: Working memory