3-DIMENSIONAL ANALYSIS OF SPONTANEOUS AND THALAMICALLY EVOKED GAMMA-OSCILLATIONS IN AUDITORY-CORTEX

The purpose of this study was to investigate interactions among lamina r cell populations producing spontaneous and evoked high-frequency (si milar to 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 stim ulation was delivered to the posterior intralaminar (PIL) nucleus. Spo ntaneous gamma oscillations, and those evoked by PIL stimulation, are confined to a location overlapping primary and secondary auditory cort ex. Current source-density and principal components analysis of lamina r recordings at this site indicate that the auditory evoked potential (AEP) complex is characterized by a stereotyped asynchronous activatio n of supra- and infragranular cell populations. Similar analysis of sp ontaneous and evoked gamma waves reveals a close spatiotemporal simila rity to the laminar AEP, indicating rhythmic interactions between supr a- and infragranular cell,groups during these oscillatory phenomena. W e conclude that neural circuit interactions producing the laminar AEP onset in auditory cortex are the same as those generating evoked and s pontaneous gamma oscillations.