SPECIFIC TONOTOPIC ORGANIZATIONS OF DIFFERENT AREAS OF THE HUMAN AUDITORY-CORTEX REVEALED BY SIMULTANEOUS MAGNETIC AND ELECTRIC RECORDINGS

This paper presents data concerning auditory evoked responses in the m iddle latency range (wave Pam/Pa) and slow latency range (wave N1m/N1) recorded from 12 subjects. It is the first group study to report mult i-channel data of both MEG and EEG recordings from the human auditory cortex. The experimental procedure involved potential and current dens ity topographical brain mapping as well as magnetic and electric sourc e analysis. Responses were compared for the following 3 stimulus frequ encies: 500, 1000 and 4000 Hz. It was found that two areas of the audi tory cortex showed mirrored tonotopic organization; one area, the sour ce of N1m/N1 wave, exhibited higher frequencies at progressively deepe r locations, while the second area, the source of the Pam/Pa wave, exh ibited higher frequencies at progressively more superficial locations. The Pa tonotopic map was located in the primary auditory cortex anter ior to the N1m/N1 mirror map. It is likely that N1m/N1 results from ac tivation of secondary auditory areas. The location of the Pa map in A1 , and its N1 mirror image in secondary auditory areas is in agreement with observations from animal studies.