Chapter 7 Oscillatory responses and gamma band activity

Abstract

Publisher Summary Sensory stimuli—olfactory, visual, or auditory—evoke periodic firing of neurons and rhythmic oscillations of membrane and local field potentials above ∼20–30 Hz. These oscillations occur in central nervous system (CNS) structures with laminar organization in bursts that are synchronous over discrete neuronal populations. Mass oscillatory responses in the same frequency range have been recorded in vivo from animals and humans. These oscillations are often referred to as gamma band (i.e. ∼20–80 Hz) activities and also known as the “40 Hz rhythm,” although the actual frequency ranges from ∼20–30 Hz to over 100 Hz and overlaps with the beta band of the EEG. Gamma rhythms are “evoked” (as responses time-locked to stimulus and hence recognizable in averages over repeated stimulation) or “induced” (as activities non-time-locked to stimulus). Oscillatory responses and gamma activities are the result of “stimuli or state changes that do not directly drive successive” oscillatory cycles. These elementary signals are thought to mediate in the spatiotemporal synchronization of activated neuronal assemblies necessary for sensory information and “cognitive” processing. The oscillatory responses have an important role in integrating visual features into coherent perceptual representations, although this concept remains controversial.