Visual gamma oscillations and excitatory/inhibitory processes in the brain
Altered balance between neural excitation and inhibition (E/I balance) characterizes many brain disorders, including such neuropsychiatric disorders as autism, schizophrenia and epilepsy. It is therefore important to be able to non-invasively measure this balance in the human brain. Rapid electromagnetic oscillations – ‘gamma oscillations’ (30 to 100 Hz) are generated by neural circuits that include excitatory and inhibitory neurons and are sensitive to changes in interactions between these neurons. Magnetoencephalography (MEG) is essentially more sensitive to gamma oscillations than other non-invasive neuroimaging methods. Therefore gamma oscillations detected by MEG can potentially provide useful information about the E/I balance in the brain.
In a series of studies, we investigated how MEG gamma oscillations induced by visual stimuli are modulated by intensity of visual input and how these modulations are related to psychophysical measure of the inhibition strength in the visual cortex and to subjective sensory sensitivity assessed with a questionnaire [1-4]. Our results indicate that excitability of the visual cortex is reflected in the pattern of changes in the power of gamma oscillations with increasing stimulation intensity. However, many questions remain for future research. What are the mechanisms behind these intensity-related changes in gamma power? Are they abnormal in people with neuropsychiatric diseases? Are they affected by pharmacological drugs?
Research in this area helps to understand the functional role of gamma – one of the major classes of brain rhythms. Moreover, they may help to develop non-invasive measures of homeostatic regulation of the excitation/inhibition balance in brain disorders.
Figure 1. Modulation of gamma oscillations by velocity of visual motion. The excitatory drive to the visual cortex increases with increasing velocity of visual motion. This increase first leads to the increase in gamma power (from 0°/s to 1.2°/s). However yet stronger increase in motion velocity/ stimulation intensity (velocity >1.2°/s) results in gamma suppression. The intensity-related gamma suppression may reflect down-regulation of growing excitation in visual networks (Orekhova et al. Sci Rep 2018).
1. Orekhova EV, Prokofyev AO, Nikolaeva AY, Schneiderman JF, Stroganova TA: Additive effect of contrast and velocity suggests the role of strong excitatory drive in suppression of visual gamma response. Plos One 2020, 15(2).
2. Orekhova EV, Rostovtseva EN, Manyukhina VO, Prokofiev AO, Obukhova TS, Nikolaeva AY, Schneiderman JF, Stroganova TA: Spatial suppression in visual motion perception is driven by inhibition: Evidence from MEG gamma oscillations. Neuroimage 2020, 213.
3. Orekhova EV, Stroganova TA, Schneiderman JF, Lundstrom S, Riaz B, Sarovic D, Sysoeva OV, Brant G, Gillberg C, Hadjikhani N: Neural gain control measured through cortical gamma oscillations is associated with sensory sensitivity. Hum Brain Mapp 2019, 40(5):1583-1593.
4. Orekhova EV, Sysoeva OV, Schneiderman JF, Lundstrom S, Galuta IA, Goiaeva DE, Prokofyev AO, Riaz B, Keeler C, Hadjikhani N et al: Input-dependent modulation of MEG gamma oscillations reflects gain control in the visual cortex. Sci Rep-Uk 2018, 8