Neuronal responses to cochlear distortion products Contact information

Sensitive response to low frequency cochlear distortion products in the auditory midbrain. Abstract During auditory stimulation with several frequency components, distortion products (DP) are generated as byproduct of nonlinear cochlear amplification. After generated DP energy is 20 reemitted into the ear channel where it can be measured as distortion product otoacoustic emission (DPOAE) and it also induces an excitatory response at cochlear places related to the DP frequencies. We measured responses of 91 inferior colliculus (IC) neurons in the gerbil during two-tone stimulation with frequencies well above the unit's receptive field but adequate to generate a distinct distortion product (f2-1 or 2f1-f2) at the unit's characteristic frequency (CF). 25 Neuronal responses to DPs could be accounted for by the simultaneously measured DPOAEs for DP frequencies above 1.3 kHz. For DP frequencies below 1.3 kHz (n = 25) there was a discrepancy between intracochlear DP magnitude and DPOAE level and most neurons responded as if the intracochlear DP level was significantly higher than the DPOAE level in the ear channel. In 12 % of those low frequency neurons, responses to the DPs could be elicited even if the 30 stimulus tone levels were below the threshold level of the neuron at CF. High intracochlear f1-f2 and 2f1-f2 DP-levels were verified by 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 35 f2-f1 distortion levels.