An Oscillatory Hierarchy Controlling Neuronal Excitability and Stimulus Processing in the Auditory Cortex

TLDR

EEG oscillations are hypothesized to reflect cyclical variations in neuronal excitability, yet no unifying theory of EEG organization exists and the role of ongoing activity in sensory processing remains controversial. The study aims to determine whether the hierarchical organization of ambient oscillatory activity allows the auditory cortex to structure its temporal activity pattern to optimize processing of rhythmic inputs. The authors analyzed laminar profiles of synaptic activity (current source density) and multiunit activity, both spontaneous and stimulus-driven, in primary auditory cortex of awake macaque monkeys. The EEG is hierarchically organized with delta phase modulating theta amplitude and theta phase modulating gamma amplitude, and this oscillatory hierarchy controls baseline excitability and thus stimulus‑related responses in a neuronal ensemble.

Abstract

EEG oscillations are hypothesized to reflect cyclical variations in the neuronal excitability, with particular frequency bands reflecting differing spatial scales of brain operation. However, despite decades of clinical and scientific investigation, there is no unifying theory of EEG organization, and the role of ongoing activity in sensory processing remains controversial. This study analyzed laminar profiles of synaptic activity [current source density CSD] and multiunit activity (MUA), both spontaneous and stimulus-driven, in primary auditory cortex of awake macaque monkeys. Our results reveal that the EEG is hierarchically organized; delta (1–4 Hz) phase modulates theta (4–10 Hz) amplitude, and theta phase modulates gamma (30–50 Hz) amplitude. This oscillatory hierarchy controls baseline excitability and thus stimulus-related responses in a neuronal ensemble. We propose that the hierarchical organization of ambient oscillatory activity allows auditory cortex to structure its temporal activity pattern so as to optimize the processing of rhythmic inputs.