scholarly journals Auditory brainstem models: adapting cochlear nuclei improve spatial encoding by the medial superior olive in reverberation

2019 ◽  
Author(s):  
Andrew Brughera ◽  
Jason Mikiel-Hunter ◽  
Mathias Dietz ◽  
David McAlpine
Keyword(s):  
Spatial Information ◽  
Interaural Time Difference ◽  
Auditory Pathway ◽  
Auditory Brainstem ◽  
Coincidence Detection ◽  
Type Model ◽  
Medial Superior Olive ◽  
Sound Energy ◽  
Superior Olive ◽  
Cochlear Nuclei

AbstractListeners perceive sound-energy as originating from the direction of its source, even as direct sound is followed milliseconds later by reflected sound from multiple different directions. Early-arriving sound is emphasised in the ascending auditory pathway, including the medial superior olive (MSO) where binaural neurons encode the interaural time difference (ITD) cue for spatial location. Behaviourally, weighting of ITD conveyed during rising sound-energy is stronger at 600 Hz, a frequency with higher reverberant energy, than at 200 Hz where reverberant energy is lower. Here we computationally explore the combined effectiveness of adaptation before ITD-encoding, and excitatory binaural coincidence detection within MSO neurons, in emphasising ITD conveyed in early-arriving sound. With excitatory inputs from adapting model spherical bushy cells (SBCs) of the bilateral cochlear nuclei, a Hodgkin-Huxley-type model MSO neuron reproduces the frequency-dependent emphasis of rising vs. peak sound-energy in ITD-encoding. Maintaining the adaptation in model SBCs, and adjusting membrane speed in model MSO neurons, hemispheric populations of model SBCs and MSO neurons, with simplified membranes for computational efficiency, also reproduce the stronger weighting of ITD information conveyed during rising sound-energy at 600 Hz compared to 200 Hz. This hemispheric model further demonstrates a link between strong weighting of spatial information during rising sound-energy, and correct unambiguous lateralisation of reverberant speech.

Frequency-dependent interaural delays in the medial superior olive: implications for interaural cochlear delays

2011 ◽  
Vol 106 (4) ◽  
pp. 1985-1999 ◽  
Author(s):  
Mitchell L. Day ◽  
Malcolm N. Semple
Keyword(s):  
Interaural Time Difference ◽  
Superior Olivary Complex ◽  
Medial Superior Olive ◽  
Biophysical Parameters ◽  
Tone Frequency ◽  
Frequency Dependent ◽  
Superior Olive ◽  
Interaural Phase ◽  
Cochlear Delays ◽  
Delay Component

Neurons in the medial superior olive (MSO) are tuned to the interaural time difference (ITD) of sound arriving at the two ears. MSO neurons evoke a strongest response at their best delay (BD), at which the internal delay between bilateral inputs to MSO matches the external ITD. We performed extracellular recordings in the superior olivary complex of the anesthetized gerbil and found a majority of single units localized to the MSO to exhibit BDs that shifted with tone frequency. The relation of best interaural phase difference to tone frequency revealed nonlinearities in some MSO units and others with linear relations with characteristic phase between 0.4 and 0.6 cycles. The latter is usually associated with the interaction of ipsilateral excitation and contralateral inhibition, as in the lateral superior olive, yet all MSO units exhibited evidence of bilateral excitation. Interaural cochlear delays and phase-locked contralateral inhibition are two mechanisms of internal delay that have been suggested to create frequency-dependent delays. Best interaural phase-frequency relations were compared with a cross-correlation model of MSO that incorporated interaural cochlear delays and an additional frequency-independent delay component. The model with interaural cochlear delay fit phase-frequency relations exhibiting frequency-dependent delays with precision. Another model of MSO incorporating inhibition based on realistic biophysical parameters could not reproduce observed frequency-dependent delays.

scholarly journals Physiological and anatomical investigation of the auditory brainstem in the Fat-tailed Dunnart (Sminthopsis crassicaudata)

2019 ◽  
Author(s):  
Andrew Garrett ◽  
Virginia Lannigan ◽  
Nathanael Yates ◽  
Jennifer Rodger ◽  
Wilhelmina Mulders
Keyword(s):  
Auditory System ◽  
Mammalian Species ◽  
Auditory Brainstem ◽  
Auditory Brainstem Responses ◽  
Superior Olivary Complex ◽  
Medial Superior Olive ◽  
Superior Olive ◽  
Medial Nucleus ◽  
Sminthopsis Crassicaudata ◽  
Nissl Stain

The fat-tailed Dunnart (Sminthopsis crassicaudata) is a small (10-20g) native marsupial endemic to the south west of Western Australia. Currently little is known about the auditory capabilities of the dunnart, and of marsupials in general. Consequently, this study sought to investigate several electrophysiological and anatomical properties of the dunnart auditory system. Auditory brainstem responses (ABR) were recorded to brief (5ms) tone pips at a range of frequencies (4-47.5 kHz) and intensities to determine auditory brainstem thresholds. The dunnart ABR displayed multiple distinct peaks at all test frequencies, similar to other mammalian species. ABR showed the dunnart is most sensitive to higher frequencies increasing up to 47.5 kHz. Morphological observations (Nissl stain) revealed that the auditory structures thought to contribute to the first peaks of the ABR were all distinguishable in the dunnart. Structures identified include the dorsal and ventral subdivisions of the cochlear nucleus, including a cochlear nerve root nucleus as well as several distinct nuclei in the superior olivary complex, such as the medial nucleus of the trapezoid body, lateral superior olive and medial superior olive. This study is the first to show functional and anatomical aspects of the lower part of the auditory system in the Fat-tailed Dunnart.

scholarly journals Predicting binaural responses from monaural responses in the gerbil medial superior olive

2016 ◽  
Vol 115 (6) ◽  
pp. 2950-2963 ◽  
Author(s):  
Andrius Plauška ◽  
J. Gerard Borst ◽  
Marcel van der Heijden
Keyword(s):  
Amplitude Ratio ◽  
Low Frequency ◽  
Linear Representation ◽  
Coincidence Detection ◽  
Mongolian Gerbils ◽  
Medial Superior Olive ◽  
Interaural Time Differences ◽  
Arrival Times ◽  
Superior Olive ◽  
Successful Prediction

Accurate sound source localization of low-frequency sounds in the horizontal plane depends critically on the comparison of arrival times at both ears. A specialized brainstem circuit containing the principal neurons of the medial superior olive (MSO) is dedicated to this comparison. MSO neurons are innervated by segregated inputs from both ears. The coincident arrival of excitatory inputs from both ears is thought to trigger action potentials, with differences in internal delays creating a unique sensitivity to interaural time differences (ITDs) for each cell. How the inputs from both ears are integrated by the MSO neurons is still debated. Using juxtacellular recordings, we tested to what extent MSO neurons from anesthetized Mongolian gerbils function as simple cross-correlators of their bilateral inputs. From the measured subthreshold responses to monaural wideband stimuli we predicted the rate-ITD functions obtained from the same MSO neuron, which have a damped oscillatory shape. The rate of the oscillations and the position of the peaks and troughs were accurately predicted. The amplitude ratio between dominant and secondary peaks of the rate-ITD function, captured in the width of its envelope, was not always exactly reproduced. This minor imperfection pointed to the methodological limitation of using a linear representation of the monaural inputs, which disregards any temporal sharpening occurring in the cochlear nucleus. The successful prediction of the major aspects of rate-ITD curves supports a simple scheme in which the ITD sensitivity of MSO neurons is realized by the coincidence detection of excitatory monaural inputs.

scholarly journals Physiological and anatomical investigation of the auditory brainstem in the Fat-tailed Dunnart (Sminthopsis crassicaudata)

2019 ◽  
Author(s):  
Andrew Garrett ◽  
Virginia Lannigan ◽  
Nathanael Yates ◽  
Jennifer Rodger ◽  
Wilhelmina Mulders
Keyword(s):  
Auditory System ◽  
Mammalian Species ◽  
Auditory Brainstem ◽  
Auditory Brainstem Responses ◽  
Superior Olivary Complex ◽  
Medial Superior Olive ◽  
Superior Olive ◽  
Medial Nucleus ◽  
Sminthopsis Crassicaudata ◽  
Nissl Stain

The fat-tailed Dunnart (Sminthopsis crassicaudata) is a small (10-20g) native marsupial endemic to the south west of Western Australia. Currently little is known about the auditory capabilities of the dunnart, and of marsupials in general. Consequently, this study sought to investigate several electrophysiological and anatomical properties of the dunnart auditory system. Auditory brainstem responses (ABR) were recorded to brief (5ms) tone pips at a range of frequencies (4-47.5 kHz) and intensities to determine auditory brainstem thresholds. The dunnart ABR displayed multiple distinct peaks at all test frequencies, similar to other mammalian species. ABR showed the dunnart is most sensitive to higher frequencies increasing up to 47.5 kHz. Morphological observations (Nissl stain) revealed that the auditory structures thought to contribute to the first peaks of the ABR were all distinguishable in the dunnart. Structures identified include the dorsal and ventral subdivisions of the cochlear nucleus, including a cochlear nerve root nucleus as well as several distinct nuclei in the superior olivary complex, such as the medial nucleus of the trapezoid body, lateral superior olive and medial superior olive. This study is the first to show functional and anatomical aspects of the lower part of the auditory system in the Fat-tailed Dunnart.

Enhancement of ITD Coding Within the Initial Stages of the Auditory Pathway

2010 ◽  
Vol 103 (1) ◽  
pp. 38-46 ◽  
Author(s):  
Michael Pecka ◽  
Ida Siveke ◽  
Benedikt Grothe ◽  
Nicholas A. Lesica
Keyword(s):  
Dynamic Range ◽  
Signal To Noise Ratio ◽  
Auditory Pathway ◽  
Coincidence Detection ◽  
Mammalian Brain ◽  
Medial Superior Olive ◽  
Interaural Time Differences ◽  
Dorsal Nucleus ◽  
The Individual ◽  
Two Stages

Sensory systems use a variety of strategies to increase the signal-to-noise ratio in their inputs at the receptor level. However, important cues for sound localization are not present at the individual ears but are computed after inputs from the two ears converge within the brain, and we hypothesized that additional strategies to enhance the representation of these cues might be employed in the initial stages after binaural convergence. Specifically, we investigated the transformation that takes place between the first two stages of the gerbil auditory pathway that are sensitive to differences in the arrival time of a sound at the two ears (interaural time differences; ITDs): the medial superior olive (MSO), where ITD tuning originates, and the dorsal nucleus of the lateral lemniscus (DNLL), to which the MSO sends direct projections. We use a combined experimental and computational approach to demonstrate that the coding of ITDs is dramatically enhanced between these two stages, with the mutual information in the responses of single neurons increasing by a factor of 2. We also show that this enhancement is related to an increase in dynamic range for neurons with high preferred frequencies and a decrease in variability for neurons with low preferred frequencies. These results suggest that a major role of the initial stages of the ITD pathway may be to enhance the representation created at the site of coincidence detection and illustrate the potential of this pathway as a model system for the study of strategies for enhancing sensory representations in the mammalian brain.

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