Arousal Fluctuations Govern Oscillatory Transitions Between Dominant $\gamma$ and $\alpha$ Occipital Activity During Eyes Open/Closed Conditions

Abstract

Arousal results in widespread activation of brain areas to increase their response in task and behavior relevant ways. Mediated by the Ascending Reticular Arousal System (ARAS), arousal-dependent inputs interact with neural circuitry to shape their dynamics. In the occipital cortex, such inputs may trigger shifts between dominant oscillations, where $\alpha$ activity is replaced by $\gamma$ activity, or vice versa. A salient example of this are spectral power alternations observed while eyes are opened and/or closed. These transitions closely follow fluctuations in arousal, suggesting a common origin. To better understand the mechanisms at play, we developed and analyzed a computational model composed of two modules: a thalamocortical feedback circuit coupled with a superficial cortical network. Upon activation by noise-like inputs originating from the ARAS, our model is able to demonstrate that noise-driven non-linear interactions mediate transitions in dominant peak frequency, resulting in the simultaneous suppression of $\alpha$ limit cycle activity and the emergence of $\gamma$ oscillations through coherence resonance. Reduction in input provoked the reverse effect - leading to anticorrelated transitions between $\alpha$ and $\gamma$ power. Taken together, these results shed a new light on how arousal shapes oscillatory brain activity.