Comparison of Bandwidths in the Inferior Colliculus and the Auditory Nerve. I. Measurement Using a Spectrally Manipulated Stimulus

2007 ◽  
Vol 98 (5) ◽  
pp. 2566-2579 ◽  
Author(s):  
Myles Mc Laughlin ◽  
Bram Van de Sande ◽  
Marcel van der Heijden ◽  
Philip X. Joris
Keyword(s):  
Inferior Colliculus ◽  
Auditory Nerve ◽  
Spike Timing ◽  
Temporal Coding ◽  
Broadband Noise ◽  
Auditory Periphery ◽  
Interaural Phase ◽  
Interaural Phase Difference ◽  
Frequency Components ◽  
Psychophysical Studies

A defining feature of auditory systems across animal divisions is the ability to sort different frequency components of a sound into separate neural frequency channels. Narrowband filtering in the auditory periphery is of obvious advantage for the representation of sound spectrum and manifests itself pervasively in human psychophysical studies as the critical band. Peripheral filtering also alters coding of the temporal waveform, so that temporal responses in the auditory periphery reflect both the stimulus waveform and peripheral filtering. Temporal coding is essential for the measurement of the time delay between waveforms at the two ears—a critical component of sound localization. A number of human psychophysical studies have shown a wider effective critical bandwidth with binaural stimuli than with monaural stimuli, although other studies found no difference. Here we directly compare binaural and monaural bandwidths (BWs) in the anesthetized cat. We measure monaural BW in the auditory nerve (AN) and binaural BW in the inferior colliculus (IC) using spectrally manipulated broadband noise and response metrics that reflect spike timing. The stimulus was a pair of noise tokens that were interaurally in phase for all frequencies below a certain flip frequency (fflip) and that had an interaural phase difference of π above fflip. The response was measured as a function of fflip and, using a separate stimulus protocol, as a function of interaural correlation. We find that both AN and IC filter BW depend on characteristic frequency, but that there is no difference in mean BW between the AN and IC.

scholarly journals First Spike Latency Code for Interaural Phase Difference Discrimination in the Guinea Pig Inferior Colliculus

2011 ◽  
Vol 31 (25) ◽  
pp. 9192-9204 ◽  
Author(s):  
O. Zohar ◽  
T. M. Shackleton ◽  
I. Nelken ◽  
A. R. Palmer ◽  
M. Shamir
Keyword(s):  
Guinea Pig ◽  
Inferior Colliculus ◽  
Phase Difference ◽  
Interaural Phase ◽  
Interaural Phase Difference ◽  
Spike Latency

Temporal Damping in Response to Broadband Noise. II. Auditory Nerve

2008 ◽  
Vol 99 (4) ◽  
pp. 1942-1952 ◽  
Author(s):  
Philip X. Joris ◽  
Dries H. Louage ◽  
Marcel van der Heijden
Keyword(s):  
Inferior Colliculus ◽  
Auditory Nerve ◽  
Low Frequency ◽  
Auditory Pathway ◽  
Broadband Noise ◽  
Linear Summation ◽  
Interaural Time Differences ◽  
Oscillatory Response ◽  
Original Report ◽  
Composite Curve

II. Auditory nerve. Low-frequency neurons in the inferior colliculus (IC) show a damped oscillatory response as a function of interaural time differences (ITDs) of broadband noise. It was previously shown that several features of such noise-delay functions are well predicted by the composite curve, generated by the linear summation of responses to tones with varying ITD. This indicates a surprising degree of linearity at the midbrain level of the auditory pathway. A similar comparison between responses to tones and to noise has not been made at a more peripheral, monaural level and it is therefore unclear to what extent this linearity reflects peripheral physiology. Here, we compare cat auditory nerve responses to broadband noise and to isolevel tones. We constructed shuffled autocorrelograms for responses to tones and summed across frequencies to obtain a monaural composite curve. We then compare this composite curve to the shuffled autocorrelogram of responses to broadband noise and find that the match between tonal and noise responses is poorer at the level of the auditory nerve than at the level of the IC. The apparent linearity of responses in the IC is thus even more surprising than was apparent from its original report because it results from mechanisms interposed between the auditory nerve and the IC.

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

2008 ◽  
Vol 100 (4) ◽  
pp. 2312-2327 ◽  
Author(s):  
Myles Mc Laughlin ◽  
Joelle Nsimire Chabwine ◽  
Marcel van der Heijden ◽  
Philip X. Joris
Keyword(s):  
Correlation Function ◽  
Inferior Colliculus ◽  
Auditory Nerve ◽  
Low Frequency ◽  
Population Level ◽  
Broadband Noise ◽  
Center Frequency ◽  
Future Studies ◽  
Two Populations

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.

Effects of interaural time delays of noise stimuli on low-frequency cells in the cat's inferior colliculus. III. Evidence for cross-correlation

1987 ◽  
Vol 58 (3) ◽  
pp. 562-583 ◽  
Author(s):  
T. C. Yin ◽  
J. C. Chan ◽  
L. H. Carney
Keyword(s):  
Inferior Colliculus ◽  
Acoustic Signal ◽  
Cross Correlation ◽  
Low Frequency ◽  
Nerve Fibers ◽  
Broadband Noise ◽  
The Other ◽  
Central Nucleus ◽  
Interaural Phase ◽  
Phase Relationships

1. We tested the coincidence, or cross-correlation, model of Jeffress, which proposes a neuronal mechanism for sensitivity to interaural time differences (ITDs) in low-frequency cells in the central nucleus of the inferior colliculus (ICC) of the cat. Different tokens of Gaussian noise stimuli were delivered to the two ears. We studied the neural responses to changes in ITDs of these stimuli and examined the manner in which the binaural cells responded to them. All of our results support the idea that the central binaural neurons perform an operation very similar to cross-correlation on the inputs arriving from each side. These inputs are transformed from the actual acoustic signal by the peripheral auditory system, and these transformations are reflected in the properties of the cross-correlations. 2. The responses to ITDs of identical broadband noise stimuli to the two ears varies cyclically as a function of ITD at a frequency close to the best frequency of the neuron. This cyclic response is a consequence of the narrowband filtering of the wideband acoustic signal by the auditory nerve fibers. To examine the effects of using stimuli to the two ears that were correlated to each other to different degrees, we generated pairs of noises. Each pair consisted of one standard noise, which was delivered to one ear, and a linear sum of two standard uncorrelated noises, which was delivered to the other ear. The responses of 34 neurons in the ICC to ITDs of noises with variable interaural coherence were examined. When partially correlated noises were delivered, there was a positive and approximately linear relationship between the degree of modulation of the response as a function of ITD and interaural coherence. The degree of modulation was measured by the synchronization coefficient, or vector strength, over one period of the ITD curve. 3. We examined the effects of altering the interaural phase relationships of the input noise stimuli. The phase of the noise stimuli was changed by digitally filtering the standard noise so that only a phase delay was imposed. The responses to ITDs with differing interaural phase relationships were then studied by delivering a phase-shifted noise to one ear and the standard noise to the other. The ITD curves in response to phase-shifted noise were shifted by about the same amount as the shift of the stimulus; the shift of the response was measured with respect to the case with identical noises to the two ears.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Neural coding of time-varying interaural time differences and time-varying amplitude in the inferior colliculus

2017 ◽  
Vol 118 (1) ◽  
pp. 544-563 ◽  
Author(s):  
Nathaniel Zuk ◽  
Bertrand Delgutte
Keyword(s):  
Firing Rate ◽  
Inferior Colliculus ◽  
Amplitude Modulation ◽  
Temporal Coding ◽  
Broadband Noise ◽  
Neural Mechanisms ◽  
Time Varying ◽  
Neural Correlate ◽  
Interaural Time Differences ◽  
Binaural Cues

Binaural cues occurring in natural environments are frequently time varying, either from the motion of a sound source or through interactions between the cues produced by multiple sources. Yet, a broad understanding of how the auditory system processes dynamic binaural cues is still lacking. In the current study, we directly compared neural responses in the inferior colliculus (IC) of unanesthetized rabbits to broadband noise with time-varying interaural time differences (ITD) with responses to noise with sinusoidal amplitude modulation (SAM) over a wide range of modulation frequencies. On the basis of prior research, we hypothesized that the IC, one of the first stages to exhibit tuning of firing rate to modulation frequency, might use a common mechanism to encode time-varying information in general. Instead, we found weaker temporal coding for dynamic ITD compared with amplitude modulation and stronger effects of adaptation for amplitude modulation. The differences in temporal coding of dynamic ITD compared with SAM at the single-neuron level could be a neural correlate of “binaural sluggishness,” the inability to perceive fluctuations in time-varying binaural cues at high modulation frequencies, for which a physiological explanation has so far remained elusive. At ITD-variation frequencies of 64 Hz and above, where a temporal code was less effective, noise with a dynamic ITD could still be distinguished from noise with a constant ITD through differences in average firing rate in many neurons, suggesting a frequency-dependent tradeoff between rate and temporal coding of time-varying binaural information. NEW & NOTEWORTHY Humans use time-varying binaural cues to parse auditory scenes comprising multiple sound sources and reverberation. However, the neural mechanisms for doing so are poorly understood. Our results demonstrate a potential neural correlate for the reduced detectability of fluctuations in time-varying binaural information at high speeds, as occurs in reverberation. The results also suggest that the neural mechanisms for processing time-varying binaural and monaural cues are largely distinct.

scholarly journals Neural Sensitivity to Periodicity in the Inferior Colliculus: Evidence for the Role of Cochlear Distortions

2004 ◽  
Vol 92 (3) ◽  
pp. 1295-1311 ◽  
Author(s):  
David McAlpine
Keyword(s):  
Inferior Colliculus ◽  
Basilar Membrane ◽  
Low Frequency ◽  
Neural Response ◽  
Auditory Midbrain ◽  
Discharge Rates ◽  
Interaural Phase ◽  
Neural Input ◽  
Interaural Phase Difference ◽  
Modulation Rate

Responses of low characteristic-frequency (CF) neurons in the inferior colliculus were obtained to amplitude-modulated (AM) high-frequency tones in which the modulation rate was equal to the neuron's CF. Despite all spectral components lying outside the pure tone–evoked response areas, discharge rates were modulated by the AM signals. Introducing a low-frequency tone (CF − 1 Hz) to the same ear as the AM tones produced a 1-Hz beat in the neural response. Introducing a tone (CF − 1 Hz) to the opposite ear to the AM tone also produced a beat in the neural response, with the beat at the period of the interaural phase difference between the CF − 1 Hz tone in one ear, and the AM rate in the other ear. The monaural and interaural interactions of the AM signals with introduced pure tones suggest that AM tones generate combination tones, (inter-modulation distortion) on the basilar membrane. These interact with low-frequency tones presented to the same ear to produce monaural beats on the basilar membrane, modulating the responses of inferior colliculus (IC) neurons on the 1-Hz period of the monaural beats or interacting binaurally with neural input generated in response to stimulation of the opposite ear. The auditory midbrain appears to show a robust representation of cochlear distortions generated by amplitude-modulated sounds.

The neural coding of auditory space

1989 ◽  
Vol 146 (1) ◽  
pp. 307-322 ◽  
Author(s):  
T. T. Takahashi
Keyword(s):  
Inferior Colliculus ◽  
Auditory System ◽  
Phase Difference ◽  
Neural Coding ◽  
Interaural Time Difference ◽  
Limited Range ◽  
Directional Sensitivity ◽  
Amplitude Difference ◽  
Interaural Phase ◽  
Interaural Phase Difference

The barn owl's auditory system computes interaural differences in time and amplitude and derives from them the horizontal and vertical coordinates of the sound source, respectively. Within the external nucleus of its inferior colliculus are auditory neurones, called ‘space-specific neurones’, that have spatial receptive fields. To activate a space-specific neurone, a sound must originate from a circumscribed region of space, or, if the sounds are delivered to each ear separately, using earphones, the stimuli must have the combination of interaural time and amplitude difference that simulates a sound broadcast from their receptive field. The sound-localization cues are processed in parallel, non-overlapping pathways extending from the cochlear nuclei to the subdivision of the inferior colliculus that innervates the space-specific neurones. Processing in the time pathway involves the coding of monaural phase angle, the derivation of sensitivity for interaural phase difference, and the calculation of interaural time difference (ITD) from interaural phase difference. The last process involves groups of neurones in the inferior colliculus whose collective firing signals a unique ITD, even though the activity of each constituent neurone signals multiple ITDs. The projections of these ensembles to the space-specific neurone endow the latter with a selectivity for ITD. Processing in the amplitude channel, about which less is known, initially involves an inhibitory process that sharpens the directional sensitivity of neurones in a lateral lemniscal nucleus. The inhibition is mediated by a commissural projection from the same lemniscal nucleus of the opposite side. At higher levels of the auditory system, neurones that are tuned to a limited range of interaural amplitude differences are found. It is proposed that at these higher stages, interaural amplitude difference, like ITD, is coded amidst an ensemble of neurones.

scholarly journals Temporal characteristics of neural sensitivities to the interaural phase difference in the inferior colliculus

2002 ◽  
Vol 23 (5) ◽  
pp. 286-286
Author(s):  
Shigeto Furukawa ◽  
Katuhiro Maki ◽  
Makio Kashino ◽  
Hiroshi Riquimaroux ◽  
Tatsuya Hirahara
Keyword(s):  
Inferior Colliculus ◽  
Phase Difference ◽  
Temporal Characteristics ◽  
Interaural Phase ◽  
Interaural Phase Difference

scholarly journals FM velocity selectivity in the inferior colliculus is inherited from velocity-selective inputs and enhanced by spike threshold

2011 ◽  
Vol 106 (5) ◽  
pp. 2399-2414 ◽  
Author(s):  
Joshua X. Gittelman ◽  
Na Li
Keyword(s):  
Inferior Colliculus ◽  
Auditory Nerve ◽  
Nerve Fibers ◽  
Spike Timing ◽  
Directional Selectivity ◽  
Extracellular Recordings ◽  
Spike Threshold ◽  
Velocity Selectivity ◽  
Whole Cell Recordings ◽  
Synaptic Mechanisms

Frequency modulation (FM) is computed from the temporal sequence of activated auditory nerve fibers representing different frequencies. Most studies in the inferior colliculus (IC) have inferred from extracellular recordings that the precise timing of nonselective inputs creates selectivity for FM direction and velocity (Andoni S, Li N, Pollak GD. J Neurosci 27: 4882–4893, 2007; Fuzessery ZM, Richardson MD, Coburn MS. J Neurophysiol 96: 1320–1336, 2006; Gordon M, O'Neill WE. Hear Res 122: 97–108, 1998). We recently reported that two additional mechanisms were more important than input timing for directional selectivity in some IC cells: spike threshold and inputs that were already selective (Gittelman JX, Li N, Pollak GD. J Neurosci 29: 13030–13041, 2009). Here, we show that these same mechanisms, selective inputs and spike threshold, underlie selectivity for FM velocity and intensity. From whole cell recordings in awake bats, we recorded spikes and postsynaptic potentials (PSPs) evoked by downward and upward FMs that swept identical frequencies at different velocities and intensities. To determine the synaptic mechanisms underlying PSP selectivity (relative PSP height), we derived sweep-evoked synaptic conductances. Changing FM velocity or intensity changed conductance timing and size. Modeling indicated that excitatory conductance size contributed more to PSP selectivity than conductance timing, indicating that the number of afferent spikes carried more FM information to the IC than precise spike timing. However, excitation alone produced mostly suprathreshold PSPs. Inhibition reduced absolute PSP heights, without necessarily altering PSP selectivity, thereby rendering some PSPs subthreshold. Spike threshold then sharpened selectivity in the spikes by rectifying the smaller PSPs. This indicates the importance of spike threshold, and that inhibition enhances selectivity via a different mechanism than previously proposed.

scholarly journals Pitch of harmonic complex tones: rate and temporal coding of envelope repetition rate in inferior colliculus of unanesthetized rabbits

2019 ◽  
Vol 122 (6) ◽  
pp. 2468-2485 ◽  
Author(s):  
Yaqing Su ◽  
Bertrand Delgutte
Keyword(s):  
Inferior Colliculus ◽  
Repetition Rate ◽  
Temporal Coding ◽  
Broadband Noise ◽  
Temporal Code ◽  
Rate Code ◽  
Harmonic Complex ◽  
Phase Lock ◽  
Wide Range ◽  
Complex Tones

Harmonic complex tones (HCTs) found in speech, music, and animal vocalizations evoke strong pitch percepts at their fundamental frequencies. The strongest pitches are produced by HCTs that contain harmonics resolved by cochlear frequency analysis, but HCTs containing solely unresolved harmonics also evoke a weaker pitch at their envelope repetition rate (ERR). In the auditory periphery, neurons phase lock to the stimulus envelope, but this temporal representation of ERR degrades and gives way to rate codes along the ascending auditory pathway. To assess the role of the inferior colliculus (IC) in such transformations, we recorded IC neuron responses to HCT and sinusoidally modulated broadband noise (SAMN) with varying ERR from unanesthetized rabbits. Different interharmonic phase relationships of HCT were used to manipulate the temporal envelope without changing the power spectrum. Many IC neurons demonstrated band-pass rate tuning to ERR between 60 and 1,600 Hz for HCT and between 40 and 500 Hz for SAMN. The tuning was not related to the pure-tone best frequency of neurons but was dependent on the shape of the stimulus envelope, indicating a temporal rather than spectral origin. A phenomenological model suggests that the tuning may arise from peripheral temporal response patterns via synaptic inhibition. We also characterized temporal coding to ERR. Some IC neurons could phase lock to the stimulus envelope up to 900 Hz for either HCT or SAMN, but phase locking was weaker with SAMN. Together, the rate code and the temporal code represent a wide range of ERR, providing strong cues for the pitch of unresolved harmonics. NEW & NOTEWORTHY Envelope repetition rate (ERR) provides crucial cues for pitch perception of frequency components that are not individually resolved by the cochlea, but the neural representation of ERR for stimuli containing many harmonics is poorly characterized. Here we show that the pitch of stimuli with unresolved harmonics is represented by both a rate code and a temporal code for ERR in auditory midbrain neurons and propose possible underlying neural mechanisms with a computational model.

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