Sensitivity of the neuromagnetic N100m deflection to spectral bandwidth: a function of the auditory periphery?

The amplitude of the auditory evoked field (AEF) component N100m in response to tonal stimuli of varying spectral bandwidth and periodicity was compared with simulated peripheral activity patterns of the auditory nerve (AN). The AEF of ten subjects was recorded with a 37-channel axial gradiometer system (four independent measurement sessions per hemisphere). The simulated peripheral activity was characterized using measures derived from spike probabilities of the AN. Stimuli were pure tones, narrow-band harmonic complex tones (spectrum: 4-4.8 kHz), and broad-band harmonic complex tones (spectrum: 800 Hz-4.8 kHz) with periodicities of 100, 200, and 400 Hz. The intensity of all stimuli was set to 65 dB above the absolute thresholds. Both the simulated AN activity and measured cortical response amplitudes increased consistently with spectral bandwidth. This suggests that the enhanced sensitivity of the N100m amplitude to broad-band complex tones is to some extent a function of the auditory periphery.