Stimulus-spezifische mechanische Adaptation im Innenohr während repetitiver Schallreizung
Biologie des Verhaltens und der Sinne
Zusammenfassung der Projektergebnisse
The work done in this project revealed that: 1. ABRs are a quite suitable tool for investigation of stimulus specific adaptation in the lower auditory system. In bats, due to small head size and a hypertrophied auditory system, ABRs are about 30 times larger in amplitude than in humans and very sensitive measurements on the first occurrence of stimulus specific adaptation in the auditory pathway are possible. We showed that deviant versus standard stimuli in the echolocation range at 60 kHz already induce adaptive processing at the first ABR peak. This implies that the effects are already present at the level of the cochlear nucleus or below. In humans we were not able to show significant changes in the first ABR waves, as in bats. However, this may be due to the much smaller potential size in humans, that did not allow to specifically focus on those waves. 2. Maximum amplitude differences between responses to deviants versus standards were seen for the the slow wave of the ABR response (peak 5 in humans) that is evident when reducing or switching off the low pass filter of the recording system. This wave is attributed to inferior colliculus activity. Both in bats and in humans, large and significant changes in the slow wave could be observed. 3. The effects were frequency specific. In bats, most pronounced stimulus specific adaption was found for the echolocation frequency range, both when using a pure tone of 60 kHz and a natural echolocation call as stimulus. In humans, signifcant stimulus specific adaptation was found for a low frequency chirp between 0,5 to 2 kHz but not for a high frequency chirp of 2-8 kHz. 4. Regarding the underlying neuronal mechanisms, we could demonstrate both repetition suppression when the stimulus is used as standard and deviant-related enhancement. Repetition suppression was dominant in the bat for the high frequency stimulus (60kHz) whereas enhancement was found to prevail when using a low frequency stimulus at 20 kHz that is within the communication frequency range (Wetekam et al. 2022). In humans, repetition suppression was evident when using a repetitive low frequeny chirp sequence, whereas a repetitive high frequency chirp sequence produced enhancement.
