Seeing Visual Gamma Oscillations in a New Light

Abstract

Gamma oscillations have been argued to support visual perception by synchronizing the processing and transfer of information within and across areas of visual cortex. Here, we highlight recent findings implicating the influence of color on visual gamma oscillations and how these observations may relate to local cortical tuning and organization.

Keywords: color; inhibition; orientation; primary visual cortex; tuning; vision.

Figure 1.. Schematic of Stimulus Features Influencing Gamma Generation in V1.

Visual stimuli and corresponding neural responses arranged by homogeneity of the stimulus (horizontal axis) and strength of the cortical representation for features contained in the stimulus (vertical axis). Gamma oscillations occur in response to visual features that are strongly represented in primary visual cortex and that are either homogeneous across the entire visual field (upper left) or homogeneous within the population receptive field (broken ellipse, upper right). Gamma oscillations are less reliably observed in response to stimuli that contain a heterogeneous mix of features (bottom right) or for stimuli containing features that are weakly represented in V1 (bottom left).

Figure 2.. Schematic of Joint Tuning in V1 and Possible Links to Gamma Generation.

Different types of visual input drive responses at the single-cell (A) and population level (B). On the left, we schematize individual cells in V1 with joint tuning for orientation and color (C). On the right, we speculate on how large gratings and uniform red color stimuli could activate an overlapping subset of cells within the orientation and color feature maps [(D) highlighted cells], which are highly interconnected (broken lines) and recruit similar recurrent networks, leading to large gamma responses (one measure of population activity). Note that the cortical feature maps depicted here are highly schematized and do not accurately represent either the functional organization of feature maps or the nature of the excitatory and inhibitory interactions within those maps. How to reconcile single-cell and population-level stimulus–response mappings is a challenge for future studies.