High Gamma Activity in Response to Deviant Auditory Stimuli Recorded Directly From Human Cortex

1 Department of Psychology and Helen Wills Neuroscience Institute, University of California, Berkeley, California; 2 Department of Psychology, The Hebrew University of Jerusalem, Jerusalem, Israel; and 3 Department of Neurological Surgery, University of California, San Francisco, California Submitted 29 March 2005; accepted in final form 1 August 2005 We recorded electrophysiological responses from the left frontal and temporal cortex of awake neurosurgical patients to both repetitive background and rare deviant auditory stimuli. Prominent sensory event-related potentials (ERPs) were recorded from auditory association cortex of the temporal lobe and adjacent regions surrounding the posterior Sylvian fissure. Deviant stimuli generated an additional longer latency mismatch response, maximal at more anterior temporal lobe sites. We found low gamma (30–60 Hz) in auditory association cortex, and we also show the existence of high-frequency oscillations above the traditional gamma range (high gamma, 60–250 Hz). Sensory and mismatch potentials were not reliably observed at frontal recording sites. We suggest that the high gamma oscillations are sensory-induced neocortical ripples, similar in physiological origin to the well-studied ripples of the hippocampus. Address for reprint requests and other correspondence: E. Edwards, Dept. of Psychology and Helen Wills Neuroscience Inst., Univ. of California, 132 Barker Hall, Berkeley, CA 94720 (E-mail: erik{at}socrates.berkeley.edu )