Sensitive Response to Low-Frequency Cochlear Distortion Products in the Auditory Midbrain

Abstract

Abel C, Kössl M. Sensitive response to low-frequency cochlear distortion products in the auditory midbrain. J Neurophysiol 101: 1560 -1574, 2009. First published November 26, 2008 doi:10.1152/jn.90805.2008. During auditory stimulation with several frequency components, distortion products (DPs) are generated as byproduct of nonlinear cochlear amplification. After generated, DP energy is reemitted into the ear channel where it can be measured as DP 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-f1 or 2f1-f2) at the unit's characteristic frequency (CF). Neuronal responses to DPs could be accounted for by the simultaneously measured DPOAEs for DP frequencies Ͼ1.3 kHz. For DP frequencies Ͻ1.3 kHz (n ϭ 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 stimulus tone levels were below the threshold level of the neuron at CF. High intracochlear f2-f1 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 f2-f1 distortion levels.

Stimulus-Specific Adaptation in the Gerbil Primary Auditory Thalamus Is the Result of a Fast Frequency-Specific Habituation and Is Regulated by the Corticofugal System

“…We calculated the mean plus 1 SD of the interstimulus activity level directly preceding stimulus onset (100 ms time window) and added 10% of the maximum spike activity of all frequency/level combinations to determine threshold activity. The neuronal frequency response area (tuning curve) was defined by linear interpolation of threshold activity in the frequency/level response matrix (Matlab function contour) (Abel and Kössl, 2009). Only the responses to stimulation frequencies within this tuning curve were further analyzed, and for the oddball paradigm, both frequencies of a stimulation pair had to be enclosed.…”

Efficient Encoding of Vocalizations in the Auditory Midbrain

“…The distortion product with the highest intensity generated through this mechanism ( f 2 Ϫ f 1 ) falls within the FRA of this neuron, perhaps causing its response. Neural sensitivity to cochlear distortion products has been documented previously throughout the auditory system (Goldstein and Kiang, 1968;McAlpine, 2004;Abel and Kössl, 2009;Portfors et al, 2009) and has been proposed as a mechanism for providing sensory cues in communication Warren et al, 2009). …”

Auditory cortex of newborn bats is prewired for echolocation

“…To sort action potentials, the first three principle components of spike waveforms were calculated 40 . To separate spikes originating from different neurons, an automatic clustering algorithm 'KlustaKwik' based on the expectation-maximization algorithm was fed with the first three principle components of each spike and then clusters were selected manually 40 .…”

“…To separate spikes originating from different neurons, an automatic clustering algorithm 'KlustaKwik' based on the expectation-maximization algorithm was fed with the first three principle components of each spike and then clusters were selected manually 40 . We did not distinguish between single-and multi-unit responses.…”