Alpha oscillations control cortical gain by modulating excitatory-inhibitory background activity

The first recordings of human brain activity in 1929 revealed a striking 8-12 Hz oscillation in the visual cortex. During the intervening 90 years, these alpha oscillations have been linked to numerous physiological and cognitive processes. However, because of the vast and seemingly contradictory cognitive and physiological processes to which it has been related, the physiological function of alpha remains unclear. We identify a novel neural circuit mechanism—the modulation of both excitatory and inhibitory neurons in a balanced configuration—by which alpha can modulate gain. We find that this model naturally unifies the prior, highly diverse reports on alpha dynamics, while making the novel prediction that alpha rhythms have two functional roles: a sustained high-power mode that suppresses cortical gain and a weak, bursting mode that enhances gain. Summary: Alpha oscillations—ubiquitous in the primate brain—control neuronal gain via two mechanisms: sustained to suppress gain and bursting to enhance it.