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Shani Offen, Justin Gardner, Denis Schluppeck, David Heeger; Distinct roles for frontal and parietal cortex in visual working memory and attention. Journal of Vision 2009;9(8):168. doi: 10.1167/9.8.168.
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© ARVO (1962-2015); The Authors (2016-present)
Objective: How do higher visual areas contribute to the cognitive control of visual processing in the human brain?
Methods: Subjects were scanned (3T fMRI, BOLD) while performing two tasks designed to probe visual working memory and visual attention. (1) Delayed comparison: A high-contrast grating (randomized orientation and spatial frequency) was briefly (200 ms) presented within an annulus (1–3°) around fixation. After a variable delay (1–16s), a second high-contrast grating was briefly presented with near-threshold changes in orientation and spatial frequency. Subjects were cued to discriminate either the change in orientation or in spatial frequency. (2) Detection: Stimuli were identical to delayed comparison, except that the contrast of the final target grating was at detection threshold, and the gratings' orientations were chosen independently. Subjects detected the presence or absence of the target grating.
Results: Our earlier study (Offen, Schluppeck & Heeger, Vision Research, 2008) reported a dissociation in visual cortex, with sustained delay-period activity only during detection. In the present study, frontal and parietal cortex exhibited patterns of activity that were different from one another, but similar for the two tasks. Consistent with previous reports, the superior precentral sulcus (sPCS, putative human FEF) showed sustained delay-period activity for both tasks; no other frontal or parietal areas showed evidence of sustained activity for either task. In particular, the intraparietal sulcus (IPS) did not show evidence of sustained delay-period activity, as might have been expected.
Conclusion: It is widely believed that sustained delay-period activity in visual cortex is controlled by top-down influences. If so, our results suggest that sPCS is driving delay-period activity in visual cortex, but only during detection, not delayed comparison. Because delay-period activity is evident in sPCS for both tasks, there must be either a gating mechanism or distinct subpopulations of neurons that determine when sPCS sustains activity in sensory cortex.
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