Three-dimensional analysis of spontaneous and thalamically evoked gamma oscillations in auditory cortex.

The purpose of this study was to investigate interactions among laminar cell populations producing spontaneous and evoked high-frequency (approximately 40 Hz) gamma oscillations in auditory cortex. Electrocortical oscillations were recorded using a 64-channel epipial electrode array and a 16-channel linear laminar electrode array while electrical stimulation was delivered to the posterior intralaminar (PIL) nucleus. Spontaneous gamma oscillations, and those evoked by PIL stimulation, are confined to a location overlapping primary and secondary auditory cortex. Current source-density and principal components analysis of laminar recordings at this site indicate that the auditory evoked potential (AEP) complex is characterized by a stereotyped asynchronous activation of supra- and infragranular cell populations. Similar analysis of spontaneous and evoked gamma waves reveals a close spatiotemporal similarity to the laminar AEP, indicating rhythmic interactions between supra- and infragranular cell groups during these oscillatory phenomena. We conclude that neural circuit interactions producing the laminar AEP onset in auditory cortex are the same as those generating evoked and spontaneous gamma oscillations.