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Noninvasive fMRI investigation of interaural level difference processing in the rat auditory subcortex.

Lau C, Zhang JW, Cheng JS, Zhou IY, Cheung MM, Wu EX - PLoS ONE (2013)

Bottom Line: Our current understanding of ILD encoding has come primarily from invasive studies of individual structures, which have implicated subcortical structures such as the cochlear nucleus (CN), superior olivary complex (SOC), lateral lemniscus (LL), and inferior colliculus (IC).For all three regions, the larger amplitude response is located in the hemisphere contralateral from the higher SPL stimulus.This study is the first step towards future studies examining subcortical binaural processing and sound localization in animal models of hearing.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Pokfulam, Hong Kong, China.

ABSTRACT

Objective: Interaural level difference (ILD) is the difference in sound pressure level (SPL) between the two ears and is one of the key physical cues used by the auditory system in sound localization. Our current understanding of ILD encoding has come primarily from invasive studies of individual structures, which have implicated subcortical structures such as the cochlear nucleus (CN), superior olivary complex (SOC), lateral lemniscus (LL), and inferior colliculus (IC). Noninvasive brain imaging enables studying ILD processing in multiple structures simultaneously.

Methods: In this study, blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) is used for the first time to measure changes in the hemodynamic responses in the adult Sprague-Dawley rat subcortex during binaural stimulation with different ILDs.

Results and significance: Consistent responses are observed in the CN, SOC, LL, and IC in both hemispheres. Voxel-by-voxel analysis of the change of the response amplitude with ILD indicates statistically significant ILD dependence in dorsal LL, IC, and a region containing parts of the SOC and LL. For all three regions, the larger amplitude response is located in the hemisphere contralateral from the higher SPL stimulus. These findings are supported by region of interest analysis. fMRI shows that ILD dependence occurs in both hemispheres and multiple subcortical levels of the auditory system. This study is the first step towards future studies examining subcortical binaural processing and sound localization in animal models of hearing.

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BOLD signal ratio slope map.BOLD signal ratio slope map computed (refer to methods for computation details) from the animal in Figs. 2 and 3. Slope is color coded from −8×10−2%/dB to 8×10−2%/dB and only activated voxels in Fig. 2 are color coded. Positive slope indicates the signal is greater at positive ILDs or when left ear SPL is greater than right ear SPL. Similarly, negative slope indicates the signal is greater at negative ILDs. Negative slope voxels are located in the left hemisphere CoN, SOC/LL, DLL, and IC and the right hemisphere CN. Positive slope voxels are located in the right hemisphere CoN, SOC/LL, DLL, and IC and left hemisphere CN.
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pone-0070706-g004: BOLD signal ratio slope map.BOLD signal ratio slope map computed (refer to methods for computation details) from the animal in Figs. 2 and 3. Slope is color coded from −8×10−2%/dB to 8×10−2%/dB and only activated voxels in Fig. 2 are color coded. Positive slope indicates the signal is greater at positive ILDs or when left ear SPL is greater than right ear SPL. Similarly, negative slope indicates the signal is greater at negative ILDs. Negative slope voxels are located in the left hemisphere CoN, SOC/LL, DLL, and IC and the right hemisphere CN. Positive slope voxels are located in the right hemisphere CoN, SOC/LL, DLL, and IC and left hemisphere CN.

Mentions: ILD dependence is quantified by the BOLD signal ratio slope map shown in Fig. 4 (refer to methods section for computation details). Positive slope indicates the BOLD signal is greater at positive ILDs or when left ear SPL is greater than right ear SPL. Similarly, negative slope indicates the signal is greater at negative ILDs. Only the slope at activated voxels in Fig. 2 are color coded. Negative slope voxels are located in the left hemisphere SOC/LL (slice 3), DLL (slice 3), and IC (slices 2 to 4) and right hemisphere CN (slices 1 to 2). Positive slope voxels are located in the right hemisphere SOC/LL (slice 3), DLL (slice 3), and IC (slices 2 to 4) and left hemisphere CN (slices 1 to 2). This indicates the SOC/LL, DLL, and IC have higher BOLD signal when the stimulation SPL is higher in the contralateral ear. The CN has higher BOLD signal when the stimulation SPL is higher in the ipsilateral ear. Refer to Fig. S2 for the time courses measured from the CN, SOC/LL, DLL, and IC.


Noninvasive fMRI investigation of interaural level difference processing in the rat auditory subcortex.

Lau C, Zhang JW, Cheng JS, Zhou IY, Cheung MM, Wu EX - PLoS ONE (2013)

BOLD signal ratio slope map.BOLD signal ratio slope map computed (refer to methods for computation details) from the animal in Figs. 2 and 3. Slope is color coded from −8×10−2%/dB to 8×10−2%/dB and only activated voxels in Fig. 2 are color coded. Positive slope indicates the signal is greater at positive ILDs or when left ear SPL is greater than right ear SPL. Similarly, negative slope indicates the signal is greater at negative ILDs. Negative slope voxels are located in the left hemisphere CoN, SOC/LL, DLL, and IC and the right hemisphere CN. Positive slope voxels are located in the right hemisphere CoN, SOC/LL, DLL, and IC and left hemisphere CN.
© Copyright Policy
Related In: Results  -  Collection

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getmorefigures.php?uid=PMC3733930&req=5

pone-0070706-g004: BOLD signal ratio slope map.BOLD signal ratio slope map computed (refer to methods for computation details) from the animal in Figs. 2 and 3. Slope is color coded from −8×10−2%/dB to 8×10−2%/dB and only activated voxels in Fig. 2 are color coded. Positive slope indicates the signal is greater at positive ILDs or when left ear SPL is greater than right ear SPL. Similarly, negative slope indicates the signal is greater at negative ILDs. Negative slope voxels are located in the left hemisphere CoN, SOC/LL, DLL, and IC and the right hemisphere CN. Positive slope voxels are located in the right hemisphere CoN, SOC/LL, DLL, and IC and left hemisphere CN.
Mentions: ILD dependence is quantified by the BOLD signal ratio slope map shown in Fig. 4 (refer to methods section for computation details). Positive slope indicates the BOLD signal is greater at positive ILDs or when left ear SPL is greater than right ear SPL. Similarly, negative slope indicates the signal is greater at negative ILDs. Only the slope at activated voxels in Fig. 2 are color coded. Negative slope voxels are located in the left hemisphere SOC/LL (slice 3), DLL (slice 3), and IC (slices 2 to 4) and right hemisphere CN (slices 1 to 2). Positive slope voxels are located in the right hemisphere SOC/LL (slice 3), DLL (slice 3), and IC (slices 2 to 4) and left hemisphere CN (slices 1 to 2). This indicates the SOC/LL, DLL, and IC have higher BOLD signal when the stimulation SPL is higher in the contralateral ear. The CN has higher BOLD signal when the stimulation SPL is higher in the ipsilateral ear. Refer to Fig. S2 for the time courses measured from the CN, SOC/LL, DLL, and IC.

Bottom Line: Our current understanding of ILD encoding has come primarily from invasive studies of individual structures, which have implicated subcortical structures such as the cochlear nucleus (CN), superior olivary complex (SOC), lateral lemniscus (LL), and inferior colliculus (IC).For all three regions, the larger amplitude response is located in the hemisphere contralateral from the higher SPL stimulus.This study is the first step towards future studies examining subcortical binaural processing and sound localization in animal models of hearing.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Biomedical Imaging and Signal Processing, The University of Hong Kong, Pokfulam, Hong Kong, China.

ABSTRACT

Objective: Interaural level difference (ILD) is the difference in sound pressure level (SPL) between the two ears and is one of the key physical cues used by the auditory system in sound localization. Our current understanding of ILD encoding has come primarily from invasive studies of individual structures, which have implicated subcortical structures such as the cochlear nucleus (CN), superior olivary complex (SOC), lateral lemniscus (LL), and inferior colliculus (IC). Noninvasive brain imaging enables studying ILD processing in multiple structures simultaneously.

Methods: In this study, blood oxygenation level-dependent (BOLD) functional magnetic resonance imaging (fMRI) is used for the first time to measure changes in the hemodynamic responses in the adult Sprague-Dawley rat subcortex during binaural stimulation with different ILDs.

Results and significance: Consistent responses are observed in the CN, SOC, LL, and IC in both hemispheres. Voxel-by-voxel analysis of the change of the response amplitude with ILD indicates statistically significant ILD dependence in dorsal LL, IC, and a region containing parts of the SOC and LL. For all three regions, the larger amplitude response is located in the hemisphere contralateral from the higher SPL stimulus. These findings are supported by region of interest analysis. fMRI shows that ILD dependence occurs in both hemispheres and multiple subcortical levels of the auditory system. This study is the first step towards future studies examining subcortical binaural processing and sound localization in animal models of hearing.

Show MeSH
Related in: MedlinePlus