Comparison of Bandwidths in the Inferior Colliculus and the Auditory Nerve. II: Measurement Using a Temporally Manipulated Stimulus

Abstract

Mc Laughlin M, Chabwine JN, van der Heijden M, Joris PX.Comparison of bandwidths in the inferior colliculus and the auditory nerve. II: measurement using a temporally manipulated stimulus. J Neurophysiol 100: 2312-2327, 2008. First published August 13, 2008 doi:10.1152/jn.90252.2008. To localize low-frequency sounds, humans rely on an interaural comparison of the temporally encoded sound waveform after peripheral filtering. This process can be compared with cross-correlation. For a broadband stimulus, after filtering, the correlation function has a damped oscillatory shape where the periodicity reflects the filter's center frequency and the damping reflects the bandwidth (BW). The physiological equivalent of the correlation function is the noise delay (ND) function, which is obtained from binaural cells by measuring response rate to broadband noise with varying interaural time delays (ITDs). For monaural neurons, delay functions are obtained by counting coincidences for varying delays across spike trains obtained to the same stimulus. Previously, we showed that BWs in monaural and binaural neurons were similar. However, earlier work showed that the damping of delay functions differs significantly between these two populations. Here, we address this paradox by looking at the role of sensitivity to changes in interaural correlation. We measured delay and correlation functions in the cat inferior colliculus (IC) and auditory nerve (AN). We find that, at a population level, AN and IC neurons with similar characteristic frequencies (CF) and BWs can have different responses to changes in correlation. Notably, binaural neurons often show compression, which is not found in the AN and which makes the shape of delay functions more invariant with CF at the level of the IC than at the AN. We conclude that binaural sensitivity is more dependent on correlation sensitivity than has hitherto been appreciated and that the mechanisms underlying correlation sensitivity should be addressed in future studies.

Fine frequency tuning in monkey auditory cortex and thalamus

“…Rhode et al (2010) concluded that frequency tuning in marmoset and squirrel monkey cochlear nucleus neurons was similar to the auditory nerve tuning found in other species. Earlier studies showed that frequency tuning inferior colliculus (IC) units was comparable to that observed in the auditory nerve in awake monkeys (Ryan and Miller 1978) or in cats (McLaughlin et al 2008;Ramachandran et al 1999), but there may be slight sharpening in the IC of bats (Haplea et al 1994;Pollak and Bodenhamer 1981). Therefore, although we do not have data on the tuning of marmoset IC neurons, the data from the cochlear nuclei of marmosets and the IC of other species suggest that the fine frequency tuning observed in MGB and A1 may originate in MGB.…”

Coincidence detection in the medial superior olive: mechanistic implications of an analysis of input spiking patterns

“…From the responses to noise, we computed two “pseudobinaural” functions which together provide a characterization of the influence of two basic binaural parameters: ITD and interaural correlation (Mc Laughlin et al, 2008). By time-shifting the “ipsilateral” relative to the “contralateral” inputs different ITDs were mimicked.…”

“…The features that were examined for physiological plausibility are spectral bandwidth (BW) and dominant frequency (DF); the steepness of the rICF; the maximal rate of the NDF (peak rate); the ITD modulation of the NDF and the halfwidth of the main peak of the NDF. For each of these features we bracketed the range of acceptable values, based on the same features in data from actual binaural responses as obtained in the cat IC (Mc Laughlin et al, 2008) or in axons from presumed MSO neurons of chinchilla (Bremen and Joris, 2013). A particular simulation was only accepted if it passed all “acceptance criteria.” Below we describe every acceptance criterion.…”

“…Thus, in combination, the NDF and rICF allow us to estimate the center frequency and bandwidth of the cochlear filtering that determines a neuron's binaural temporal sensitivity. Previous work from our lab has measured these two properties for IC neurons via a fitting procedure (Mc Laughlin et al, 2008), based on a method used for psychoacoustically measured NDFs (van der Heijden and Trahiotis, 1999), and found a clear relationship between center frequency and bandwidth (BW). Here we used a similar approach to determine corresponding values for the coincidence simulation results, and then check whether these values are within the range obtained for actual binaural neurons (Mc Laughlin et al, 2008).…”

“…A third issue is that the simplest model of coincidence detection, applied to spike trains recorded from SBCs, results in outputs that deviate significantly from actual binaural responses (Mc Laughlin et al, 2008). In that work, a simple coincidence analysis was applied to responses of single axons in the trapezoid body (TB), originating from SBCs and GBCs, as well as to responses of auditory nerve (AN) fibers.…”