Spatial representation of frequency-modulated tones in gerbil auditory cortex revealed by epidural electrocorticography.

The present study investigated the topography of epidurally recorded middle latency components P1 and N1 evoked by spectrally dynamic stimuli (linearly frequency-modulated (FM) tones) with respect to the tonotopic structure of the right primary auditory cortex, field AI. Whereas the gross topography corresponded to the spectral content of the FM tones, specific tonotopic offsets were found between the potential distributions evoked by FM tones of different modulation direction (i.e. 'rising' vs. 'falling'). Potentials evoked by rising FM tones were located at tonotopic positions corresponding to higher frequencies compared with potentials evoked by falling FM tones. Data indicated that the magnitude of these offsets can be attributed to the local tonotopic resolution in AI and are not dependent on the modulation rate.