Lecture by Prof. Tatiana Stroganova: Oscillatory gamma activity in
humans: a possible role for homeostatic regulation of excitation/inhibition balance

Gamma frequency oscillations (30 to 100 Hz) are ubiquitous in the brain and are thought to be involved in multiple cognitive and perceptual processes. While the role of gamma oscillations as a basic mechanism of information processing is still debated, researchers generally agree that these oscillations may provide useful information on interaction between inhibition and excitation in neural networks. Gamma-range activity can be noninvasively recorded by magnetoencephalography (MEG) and can potentially help to assess the excitation/inhibition balance in the human brain. This may have important clinical implications, since noninvasive measures of the excitation-inhibition balance in the intact human brain are lacking. It is however still unclear which parameters of the gamma waves are most relevant. In a series of studies we investigated how visual gamma oscillations are modulated by the strength of excitatory drive and how these modulations are related to behavioral indexes of neural inhibition in typical participants and people with autism spectrum disorder.  Our results suggest that the modulation of gamma power and frequency at high stimulation intensities characterizes the capacity of inhibitory neurons to counterbalance increasing excitation in visual networks.  We argue that stimulation-related changes in gamma oscillations, rather than absolute values of their frequency or amplitude, provide important information about excitatory/inhibitory balance in healthy and diseased brain.