1 Revised sent to JNP 2 3 4 5 6 Coding of repetitive transients by auditory cortex on Heschl ’ s gyrus 7 8 9

37 38 The capacity of auditory cortex on Heschl’s gyrus (HG) to encode repetitive transients was studied in 39 human patients undergoing surgical evaluation for medically intractable epilepsy. Multi-contact depth 40 electrodes were chronically implanted in grey matter of HG. Bilaterally presented stimuli were click 41 trains varying in rate from 4 Hz to 200 Hz. Averaged evoked potentials (AEPs) and event related band 42 power (ERBP), computed from responses at each of 14 recording sites, identified two auditory fields. A 43 core field, which occupies posteromedial HG, was characterized by a robust polyphasic AEP upon 44 which could be superimposed a frequency following response (FFR). The FFR was prominent at click 45 rates below about 50 Hz, decreased rapidly as click rate was increased, but could reliably be detected at 46 click rates as high as 200 Hz. These data are strikingly similar to those obtained by others in the 47 monkey under essentially the same stimulus conditions, indicating that mechanisms underlying temporal 48 processing in the auditory core may be highly conserved across primate species. ERBP, which reflects 49 increases or decreases of both phase-locked and non-phase-locked power within given frequency bands, 50 showed stimulus-related increases in gamma band frequencies as high as 250 Hz. The AEPs recorded in 51 a belt field anterolateral to the core were typically of low amplitude, showing little or no evidence of 52 short-latency waves or an FFR, even at the lowest click rates used. The non-phase-locked component of 53 the response extracted from the ERBP showed a robust, long latency response occurring here in 54 response to the highest click rates in the series. 55 56 57 58 59 60 61 62 63 64 65