scholarly journals Pitch of Harmonic Complex Tones: Rate-Place Coding of Resolved Components in Harmonic and Inharmonic Complex Tones in Auditory Midbrain

2019 ◽  
Author(s):  
Yaqing Su ◽  
Bertrand Delgutte
Keyword(s):  
Primary Auditory Cortex ◽  
Auditory Pathway ◽  
Sound Level ◽  
Auditory Midbrain ◽  
Harmonic Complex ◽  
Local Maxima ◽  
Firing Rates ◽  
Sound Levels ◽  
Complex Tones ◽  
Frequency Components

AbstractHarmonic complex tones (HCT) commonly occurring in speech and music evoke a strong pitch at their fundamental frequency (F0), especially when they contain harmonics individually resolved by the cochlea. When all frequency components of an HCT are shifted by the same amount, the pitch of the resulting inharmonic tone (IHCT) also shifts although the envelope repetition rate is unchanged. A rate-place code whereby resolved harmonics are represented by local maxima in firing rates along the tonotopic axis has been characterized in the auditory nerve and primary auditory cortex, but little is known about intermediate processing stages. We recorded single neuron responses to HCT and IHCT with varying F0 and sound level in the inferior colliculus (IC) of unanesthetized rabbits. Many neurons showed peaks in firing rates when a low-numbered harmonic aligned with the neuron’s characteristic frequency, demonstrating “rate-place” coding. The IC rate-place code was most prevalent for F0>800 Hz, was only moderately dependent on sound level over a 40 dB range, and was not sensitive to stimulus harmonicity. A spectral receptive-field model incorporating broadband inhibition better predicted the neural responses than a purely excitatory model, suggesting an enhancement of the rate-place representation by inhibition. Some IC neurons showed facilitation in response to HCT, similar to cortical “harmonic template neurons” (Feng and Wang 2017), but to a lesser degree. Our findings shed light on the transformation of rate-place coding of resolved harmonics along the auditory pathway, and suggest a gradual emergence of harmonic templates from low to high processing centers.Significance statementHarmonic complex tones are ubiquitous in speech and music and produce strong pitch percepts in human listeners when they contain frequency components that are individually resolved by the cochlea. Here, we characterize a “rate-place” code for resolved harmonics in the auditory midbrain that is more robust across sound levels than the peripheral rate-place code and insensitive to the harmonic relationships among frequency components. We use a computational model to show that inhibition may play an important role in shaping the rate-place code. We also show that midbrain auditory neurons can demonstrate similar properties as cortical harmonic template neurons. Our study fills a gap in understanding the transformation in neural representations of resolved harmonics along the auditory pathway.

scholarly journals Transformation of spatial sensitivity along the ascending auditory pathway

2015 ◽  
Vol 113 (9) ◽  
pp. 3098-3111 ◽  
Author(s):  
Justin D. Yao ◽  
Peter Bremen ◽  
John C. Middlebrooks
Keyword(s):  
Inferior Colliculus ◽  
Primary Auditory Cortex ◽  
Noise Burst ◽  
Auditory Pathway ◽  
Sound Level ◽  
Central Nucleus ◽  
Sound Location ◽  
Spatial Sensitivity ◽  
Sound Levels ◽  
Medial Geniculate

Locations of sounds are computed in the central auditory pathway based primarily on differences in sound level and timing at the two ears. In rats, the results of that computation appear in the primary auditory cortex (A1) as exclusively contralateral hemifield spatial sensitivity, with strong responses to sounds contralateral to the recording site, sharp cutoffs across the midline, and weak, sound-level-tolerant responses to ipsilateral sounds. We surveyed the auditory pathway in anesthetized rats to identify the brain level(s) at which level-tolerant spatial sensitivity arises. Noise-burst stimuli were varied in horizontal sound location and in sound level. Neurons in the central nucleus of the inferior colliculus (ICc) displayed contralateral tuning at low sound levels, but tuning was degraded at successively higher sound levels. In contrast, neurons in the nucleus of the brachium of the inferior colliculus (BIN) showed sharp, level-tolerant spatial sensitivity. The ventral division of the medial geniculate body (MGBv) contained two discrete neural populations, one showing broad sensitivity like the ICc and one showing sharp sensitivity like A1. Dorsal, medial, and shell regions of the MGB showed fairly sharp spatial sensitivity, likely reflecting inputs from A1 and/or the BIN. The results demonstrate two parallel brainstem pathways for spatial hearing. The tectal pathway, in which sharp, level-tolerant spatial sensitivity arises between ICc and BIN, projects to the superior colliculus and could support reflexive orientation to sounds. The lemniscal pathway, in which such sensitivity arises between ICc and the MGBv, projects to the forebrain to support perception of sound location.

Leading Inhibition to Neural Oscillation Is Important for Time-Domain Processing in the Auditory Midbrain

2005 ◽  
Vol 94 (1) ◽  
pp. 314-326 ◽  
Author(s):  
Alexander V. Galazyuk ◽  
Wenyu Lin ◽  
Daniel Llano ◽  
Albert S. Feng
Keyword(s):  
Time Domain ◽  
Time Course ◽  
Sound Level ◽  
High Threshold ◽  
Auditory Midbrain ◽  
Response Latencies ◽  
Response Characteristics ◽  
Sound Levels ◽  
Discharge Patterns ◽  
Central Auditory Neurons

A number of central auditory neurons exhibit paradoxical latency shift (PLS), a response characterized by longer response latencies at higher sound levels. PLS neurons are known to play a role in target ranging for echolocating bats that emit frequency-modulated sounds. We recently reported that early inhibition of unit’s oscillatory discharges is critical for PLS in the inferior colliculus (IC) of little brown bats. The goal of this study was to determine in echolocating bats and in nonecholocating animals (frogs): 1) the detailed characteristics of PLS and whether PLS was dependent on sound level, frequency, and duration; 2) the time course of inhibition underlying PLS using a paired-pulse paradigm. We found that 22% of IC neurons in bats and 15% in frogs exhibited periodic discharge patterns in response to tone pulses at high sound levels. The firing periodicity was unit specific and independent of sound level and duration. Other IC neurons (28% in bats; 14% in frogs) exhibited PLS. These PLS neurons shared several response characteristics: 1) PLS was largely independent of sound frequency and 2) the magnitude of shift in first-spike latency was either duration dependent or duration tolerant. For PLS neurons, application of bicuculline abolished PLS and unmasked the unit’s periodical firing pattern that served as the building block for PLS. In response to paired sound pulses, PLS neurons exhibited delay-dependent response suppression, confirming that high-threshold leading inhibition was responsible for PLS. Results also revealed the timing of excitatory and inhibitory inputs underlying PLS and its role in time-domain processing.

scholarly journals Neural population encoding and decoding of sound source location across sound level in the rabbit inferior colliculus

2016 ◽  
Vol 115 (1) ◽  
pp. 193-207 ◽  
Author(s):  
Mitchell L. Day ◽  
Bertrand Delgutte
Keyword(s):  
Inferior Colliculus ◽  
Sound Source ◽  
Auditory Pathway ◽  
Relevant Information ◽  
Sound Level ◽  
Neural Population ◽  
Linear Transformations ◽  
Tuning Curves ◽  
Azimuthal Position ◽  
Sound Levels

At lower levels of sensory processing, the representation of a stimulus feature in the response of a neural population can vary in complex ways across different stimulus intensities, potentially changing the amount of feature-relevant information in the response. How higher-level neural circuits could implement feature decoding computations that compensate for these intensity-dependent variations remains unclear. Here we focused on neurons in the inferior colliculus (IC) of unanesthetized rabbits, whose firing rates are sensitive to both the azimuthal position of a sound source and its sound level. We found that the azimuth tuning curves of an IC neuron at different sound levels tend to be linear transformations of each other. These transformations could either increase or decrease the mutual information between source azimuth and spike count with increasing level for individual neurons, yet population azimuthal information remained constant across the absolute sound levels tested (35, 50, and 65 dB SPL), as inferred from the performance of a maximum-likelihood neural population decoder. We harnessed evidence of level-dependent linear transformations to reduce the number of free parameters in the creation of an accurate cross-level population decoder of azimuth. Interestingly, this decoder predicts monotonic azimuth tuning curves, broadly sensitive to contralateral azimuths, in neurons at higher levels in the auditory pathway.

Pitch vs. spectral encoding of harmonic complex tones in primary auditory cortex of the awake monkey

1998 ◽  
Vol 786 (1-2) ◽  
pp. 18-30 ◽  
Author(s):  
Yonatan I. Fishman ◽  
David H. Reser ◽  
Joseph C. Arezzo ◽  
Mitchell Steinschneider
Keyword(s):  
Auditory Cortex ◽  
Primary Auditory Cortex ◽  
Harmonic Complex ◽  
Awake Monkey ◽  
Spectral Encoding ◽  
Complex Tones

scholarly journals Level dependence of spatial processing in the primate auditory cortex

2012 ◽  
Vol 108 (3) ◽  
pp. 810-826 ◽  
Author(s):  
Yi Zhou ◽  
Xiaoqin Wang
Keyword(s):  
Auditory Cortex ◽  
Sound Field ◽  
Primary Auditory Cortex ◽  
Neural Mechanism ◽  
Stimulus Level ◽  
Sound Level ◽  
Broadband Noise ◽  
Spatial Tuning ◽  
Sound Levels ◽  
Tuning Width

Sound localization in both humans and monkeys is tolerant to changes in sound levels. The underlying neural mechanism, however, is not well understood. This study reports the level dependence of individual neurons' spatial receptive fields (SRFs) in the primary auditory cortex (A1) and the adjacent caudal field in awake marmoset monkeys. We found that most neurons' excitatory SRF components were spatially confined in response to broadband noise stimuli delivered from the upper frontal sound field. Approximately half the recorded neurons exhibited little change in spatial tuning width over a ∼20-dB change in sound level, whereas the remaining neurons showed either expansion or contraction in their tuning widths. Increased sound levels did not alter the percent distribution of tuning width for neurons collected in either cortical field. The population-averaged responses remained tuned between 30- and 80-dB sound pressure levels for neuronal groups preferring contralateral, midline, and ipsilateral locations. We further investigated the spatial extent and level dependence of the suppressive component of SRFs using a pair of sequentially presented stimuli. Forward suppression was observed when the stimuli were delivered from “far” locations, distant to the excitatory center of an SRF. In contrast to spatially confined excitation, the strength of suppression typically increased with stimulus level at both the excitatory center and far regions of an SRF. These findings indicate that although the spatial tuning of individual neurons varied with stimulus levels, their ensemble responses were level tolerant. Widespread spatial suppression may play an important role in limiting the sizes of SRFs at high sound levels in the auditory cortex.

scholarly journals Decoding sound level in the marmoset primary auditory cortex

2017 ◽  
Vol 118 (4) ◽  
pp. 2024-2033 ◽  
Author(s):  
Wensheng Sun ◽  
Ellisha N. Marongelli ◽  
Paul V. Watkins ◽  
Dennis L. Barbour
Keyword(s):  
Auditory Cortex ◽  
Auditory System ◽  
Primary Auditory Cortex ◽  
Sound Level ◽  
Central Auditory System ◽  
Sound Perception ◽  
Neuron Populations ◽  
Sound Levels ◽  
Real Neuron

Neurons that respond favorably to a particular sound level have been observed throughout the central auditory system, becoming steadily more common at higher processing areas. One theory about the role of these level-tuned or nonmonotonic neurons is the level-invariant encoding of sounds. To investigate this theory, we simulated various subpopulations of neurons by drawing from real primary auditory cortex (A1) neuron responses and surveyed their performance in forming different sound level representations. Pure nonmonotonic subpopulations did not provide the best level-invariant decoding; instead, mixtures of monotonic and nonmonotonic neurons provided the most accurate decoding. For level-fidelity decoding, the inclusion of nonmonotonic neurons slightly improved or did not change decoding accuracy until they constituted a high proportion. These results indicate that nonmonotonic neurons fill an encoding role complementary to, rather than alternate to, monotonic neurons. NEW & NOTEWORTHY Neurons with nonmonotonic rate-level functions are unique to the central auditory system. These level-tuned neurons have been proposed to account for invariant sound perception across sound levels. Through systematic simulations based on real neuron responses, this study shows that neuron populations perform sound encoding optimally when containing both monotonic and nonmonotonic neurons. The results indicate that instead of working independently, nonmonotonic neurons complement the function of monotonic neurons in different sound-encoding contexts.

scholarly journals Neuronal interaural level difference response shifts are level-dependent in the rat auditory cortex

2014 ◽  
Vol 111 (5) ◽  
pp. 930-938 ◽  
Author(s):  
Michael Kyweriga ◽  
Whitney Stewart ◽  
Michael Wehr
Keyword(s):  
Auditory Cortex ◽  
Sound Localization ◽  
Response Shift ◽  
Population Level ◽  
Auditory Pathway ◽  
Sound Level ◽  
Central Nucleus ◽  
Interaural Level Difference ◽  
Sound Levels ◽  
Behavioral Studies

How does the brain accomplish sound localization with invariance to total sound level? Sensitivity to interaural level differences (ILDs) is first computed at the lateral superior olive (LSO) and is observed at multiple levels of the auditory pathway, including the central nucleus of inferior colliculus (ICC) and auditory cortex. In LSO, this ILD sensitivity is level-dependent, such that ILD response functions shift toward the ipsilateral (excitatory) ear with increasing sound level. Thus early in the processing pathway changes in firing rate could indicate changes in sound location, sound level, or both. In ICC, while ILD responses can shift toward either ear in individual neurons, there is no net ILD response shift at the population level. In behavioral studies of human sound localization acuity, ILD sensitivity is invariant to increasing sound levels. Level-invariant sound localization would suggest transformation in level sensitivity between LSO and perception of sound sources. Whether this transformation is completed at the level of the ICC or continued at higher levels remains unclear. It also remains unknown whether perceptual sound localization is level-invariant in rats, as it is in humans. We asked whether ILD sensitivity is level-invariant in rat auditory cortex. We performed single-unit and whole cell recordings in rat auditory cortex under ketamine anesthesia and measured responses to white noise bursts presented through sealed earphones at a range of ILDs. Surprisingly, we found that with increasing sound levels ILD responses shifted toward the ipsilateral ear (which is typically inhibitory), regardless of whether cells preferred ipsilateral, contralateral, or binaural stimuli. Voltage-clamp recordings suggest that synaptic inhibition does not contribute substantially to this transformation in level sensitivity. We conclude that the level invariance of ILD sensitivity seen in behavioral studies is not present in rat auditory cortex.

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