Dissociation of Broadband High-Frequency Activity and Neuronal Firing in the Neocortex

Abstract

Broadband High-frequency Activity (BHA; 70-150 Hz), also known as “high gamma,” a key analytic signal in human intracranial (electrocorticographic; ECoG) recordings, is often assumed to reflect local neural firing (multiunit activity; MUA). As the precise physiological substrates of BHA are unknown, this assumption remains controversial. Our analysis of laminar multielectrode data from V1 and A1 in monkeys, outlines two components of stimulus-evoked BHA distributed across the cortical layers: an “early-deep” layer and a “later-superficial” layer response. Early-deep BHA had a clear local MUA correlate. Later-superficial BHA was more prominent and accounted for more of the BHA signal measured near the cortical pial surface. However, its MUA correlate is weaker and often undetectable, consistent with the view that it reflects dendritic processes separable from local neuronal firing.

Keywords: gamma, Oscillations, field potentials, broadband high-frequency activity, BHA, multi-unit activity, MUA, V1, A1, cortical layers