Die vorliegende Arbeit untersucht die neuronale Repräsentation von cochleären Verzerrungsprodukten im auditorischen Mittelhirn der Wüstenrennmaus. Die hohe Sensitivität und die gute Frequenzauflösung des Hörorgans der Säugetiere basiert auf einer aktiven mechanischen Verstärkung der schallinduzierten Basilarmembranschwingung im Innenohr. Die äußeren Haarsinneszellen, die während des Transduktionsprozesses zyklisch ihre Länge ändern und dabei zusätzliche Schwingungsenergie in das System zurückführen, sind der zugrunde liegende Motor des aktiven cochleären Verstärkers. Die stark nichtlinearen Eigenschaften dieses Verstärkers führen allerdings bei gleichzeitiger Verstärkung mehrerer Frequenzkomponenten zur Generierung von Kombinationsschwingungen, welche im Ursprungssignal nicht vorhanden sind. Wird das Ohr beispielsweise durch zwei Töne mit den Frequenzen f1 und f2 stimuliert (f1f1), DPs are generated in the region of overlap of the two stimulus travelling waves and the most distinct distortion products are the quadratic distortion-tone (f2-f1) and the cubic distortion-tone (2f1-f2). From their generation site they propagate via the cochlear fluid space in both directions, i.e. both towards the base of the cochlear where they are reversely transmitted via the middle ear into the ear channel and towards the apex of the cochlea to their characteristic frequency site where they may activate the sound transduction process and subsequent neuronal processing. In the ear channel the distortion product energy can be measured as distortion product otoacoustic emission (DPOAEs). Neuronal correlates of cochlear DPs can be measured in several brain regions along the auditory pathway. In the present Phd-thesis the neuronal correlates and the otoacoustic emissions of cochlear distortion products were measured simultaneously. By comparing the neuronal responses with the peripheral DPOAE measures possible changes of the neuronal representation of cochlear DPs should be revealed. For this purpose the electrical activity of 91 neurons in the colliculus inferior of the Mongolian gerbil was recorded while the contra lateral ear was stimulated with two high frequency stimuli and DPOAE were measured. The frequencies of the stimulus tones (f1 and f2) where chosen such that the frequency of a resulting DP (f2-f1 or 2f1-f2) matched the characteristic frequency of the recorded auditory neuron. In 95~% of all measurements a strong neuronal response could be measured during two tone stimulation which can be attributed to the intracochlear stimulation by a distinct DP. The stimulation with one of the two stimuli alone did not induce any neuronal response. In a subset of the measurements the neuronal response during two tone stimulation could be successfully canceled by a third phase adjusted tone with a frequency equal to the DP frequency what provides evidence for the intra cochlear DP as source of the neuronal response. While at DP frequencies above 1.3 kHz the neuronal responses near threshold could be well described by the DPOAE level, at lower frequencies an increasing discrepancy between intra cochlear DP level and the DPOAE level in the ear channel is obvious. Part of the low frequency neurons already responded during stimulation with the high frequency stimuli with stimulus levels at or below the neuronal threshold. Again, high intracochlear DP-levels were verified by the cancellation of the neuronal DP-response with a third phase-adjusted tone stimulus at the DP frequency. A frequency-specific reduction of middle ear gain at low frequencies is possibly involved in the reduction of DPOAE level. The results indicate that pitch-related properties of complex stimuli may be produced partially by high intracochlear f2-f1 distortion levels
