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UniversitΣt Tübingen - Lehrstuhl Tierphysiologie |
Response to exponential frequency modulations in the rat inferior colliculus
Hearing Research 98 (1996) 137-151
We examined responses to pure tones and exponentially frequency modulated (FM) stimuli in the inferior colliculus of ketamine anesthetized rats. All units responded to both, pure tone and FM stimulation; units responding selectively to FM stimuli were not found. The comparison of responses to many different FM sweeps revealed that activity was elicited when the instantaneous frequency of an FM sweep entered the unit's pure tone-tuning curve. Units were tuned to the rate of frequency modulation. Most modulation rate transfer functions had band pass characteristics. Best modulation rates covered a range from 4.8 to 1904 octaves/s with more than 90% between 10 and 400 octaves/s. In contrast to previous studies, modulation direction was not coded in unit responses. This can at least partly be attributed to the FM stimulus design which, in the present study, was adapted to the logarithmic frequency representation in the rat auditory system and carefully matched to the units' pure tone response area. In spite of the close relationship between pure tone and FM response behavior, modulatoin rate tuning cannot be completely explained on the basis of the units' pure tone responses.
auditory system, FM, modulation rate tuning, direction selective, single-unit