Fig. 1.

Circuitry of alpha and gamma rhythms in visual cortex. (A) van Kerkoerle et al. simultaneously recorded multiunit activity and field potentials from regions with overlapping receptive fields in V1 and V4. A feedforward γ rhythm (40–90 Hz; V1–V4) and feedback α rhythm (8–12 Hz; V4–V1) were identified. (B) γ rhythms in superficial layers of V4 and α rhythms in deep layers of V4 have previously been identified (7). That finding is depicted here with plots of intralaminar coherence vs. frequency. (C) Through Granger causality analysis, γ rhythms (red arrows) were found to originate in layer 4 of V1 and spread to superficial and deep layers of V1. The γ rhythm then was directed from superficial layers of V1–V4. Feedback α rhythms from the deep layers of V4 were directed toward deep and superficial layers of V1 (blue arrows). Dominant field potential power is represented by laminar shading (red for γ and blue for α).