The effects of habituation and lateral inhibition on cortical auditory evoked magnetic fields have been studied in five subjects. For this investigation a novel stimulus paradigm has been developed. Short time habituation was induced by a masking noise, which was defined in frequency domain by alternated pass and stop bands. The spectral power of the resulting "comb-filtered noise" was maximal in the pass-bands, which was spaced by half-octave distances in the frequency range from 0.5 to 3KHz and was minimal in the stop-bands between pass-bands. Two stimulus signals were applied, consisting of 40Hz-amplitude modulated complex sounds with spectral components at frequencies corresponding either to the center frequencies of the comb-filter's pass-bands or the corresponding stop-bands. The auditory response to the stimulus with spectral components in the stop-bands was more suppressed than the responses to the pass-band stimuli in the right hemisphere after listening to the comb-filtered noise for 20 seconds. This result suggests that the lateral inhibition might have stronger effect than the direct habituation. The obtained results contribute to the development of a model for centrally generated tinnitus.
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