Specific tonotopic organizations of different areas of the human auditory cortex revealed by simultaneous magnetic and electric recordings

Abstract

This paper presents data concerning auditory evoked responses in the middle latency range (wave Pam/ Pa) and slow latency range (wave Nlm/Nl) recorded from 12 subjects. It is the first group study to report multi-channel data of both MEG and EEG recordings from the human auditory cortex. The experimental procedure involved potential and current density topographical brain mapping as well as magnetic and electric source analysis. Responses were compared for the following 3 stimulus frequencies: 500, 1000 and 4000 Hz. It was found that two areas of the auditory cortex showed mirrored tonotopic organization; one area, the source of Nlm/Nl wave, exhibited higher frequencies at progressively deeper locations, while the second area, the source of the Pam/Pa wave, exhibited higher frequencies at progressively more superficial locations. The Pa tonotopic map was located in the primary auditory cortex anterior to the Nlm/Nl mirror map. It is likely that Nlm/Nl results from activation of secondary auditory areas. The location of the Pa map in AI, and its NI mirror image in secondary auditory areas is in agreement with observations from animal studies.