Limits...
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.

Show MeSH

Related in: MedlinePlus

Correlation coefficient map.Correlation coefficient (r) map computed from the average spin-echo echo planar imaging images of a representative animal. Averaging was performed across the seven ILDs. The left and right hemispheres of the brain are labeled. The image slices are labeled one to four and the distances from their centers to Bregma are 10.9, 9.7, 8.5, and 7.3 mm, respectively. Groups of activated voxels with r >0.22 and in clusters of three voxels are color coded and can be found in the cochlear nerve (CoN), cochlear nucleus (CN), superior olivary complex (SOC), dorsal lateral lemniscus (DLL), ventral and intermediate lateral lemnisci (VLL), inferior colliculus (IC), and crus1 of the ansiform lobule of the cerebellum (Crus1). Regions of interest (ROIs) are drawn around activated voxels in the CN, SOC/LL, DLL, and IC of both hemispheres. Identification of different voxel groups was aided by the rat brain atlas. SOC/LL refers to a group of voxels that covers parts of the SOC and lateral lemniscus.
© Copyright Policy
Related In: Results  -  Collection


getmorefigures.php?uid=PMC3733930&req=5

pone-0070706-g002: Correlation coefficient map.Correlation coefficient (r) map computed from the average spin-echo echo planar imaging images of a representative animal. Averaging was performed across the seven ILDs. The left and right hemispheres of the brain are labeled. The image slices are labeled one to four and the distances from their centers to Bregma are 10.9, 9.7, 8.5, and 7.3 mm, respectively. Groups of activated voxels with r >0.22 and in clusters of three voxels are color coded and can be found in the cochlear nerve (CoN), cochlear nucleus (CN), superior olivary complex (SOC), dorsal lateral lemniscus (DLL), ventral and intermediate lateral lemnisci (VLL), inferior colliculus (IC), and crus1 of the ansiform lobule of the cerebellum (Crus1). Regions of interest (ROIs) are drawn around activated voxels in the CN, SOC/LL, DLL, and IC of both hemispheres. Identification of different voxel groups was aided by the rat brain atlas. SOC/LL refers to a group of voxels that covers parts of the SOC and lateral lemniscus.

Mentions: Regions of interest (ROIs) were also drawn around the cochlear nucleus, superior olivary complex/lateral lemniscus (a group of voxels that borders the SOC and LL), dorsal lateral lemniscus, and inferior colliculus in each hemisphere using the rat brain atlas [34] as a guide. The precise borders of the ROIs, refer to Fig. 2, were set to include only voxels with r >0.22 and in clusters of three voxels (Stimulate 6.0, University of Minnesota, USA). ROIs were drawn for each animal. For ROIs, BOLD signal ratios were computed by dividing the average BOLD signal of the left hemisphere ROI by that of the corresponding right hemisphere ROI.


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)

Correlation coefficient map.Correlation coefficient (r) map computed from the average spin-echo echo planar imaging images of a representative animal. Averaging was performed across the seven ILDs. The left and right hemispheres of the brain are labeled. The image slices are labeled one to four and the distances from their centers to Bregma are 10.9, 9.7, 8.5, and 7.3 mm, respectively. Groups of activated voxels with r >0.22 and in clusters of three voxels are color coded and can be found in the cochlear nerve (CoN), cochlear nucleus (CN), superior olivary complex (SOC), dorsal lateral lemniscus (DLL), ventral and intermediate lateral lemnisci (VLL), inferior colliculus (IC), and crus1 of the ansiform lobule of the cerebellum (Crus1). Regions of interest (ROIs) are drawn around activated voxels in the CN, SOC/LL, DLL, and IC of both hemispheres. Identification of different voxel groups was aided by the rat brain atlas. SOC/LL refers to a group of voxels that covers parts of the SOC and lateral lemniscus.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3733930&req=5

pone-0070706-g002: Correlation coefficient map.Correlation coefficient (r) map computed from the average spin-echo echo planar imaging images of a representative animal. Averaging was performed across the seven ILDs. The left and right hemispheres of the brain are labeled. The image slices are labeled one to four and the distances from their centers to Bregma are 10.9, 9.7, 8.5, and 7.3 mm, respectively. Groups of activated voxels with r >0.22 and in clusters of three voxels are color coded and can be found in the cochlear nerve (CoN), cochlear nucleus (CN), superior olivary complex (SOC), dorsal lateral lemniscus (DLL), ventral and intermediate lateral lemnisci (VLL), inferior colliculus (IC), and crus1 of the ansiform lobule of the cerebellum (Crus1). Regions of interest (ROIs) are drawn around activated voxels in the CN, SOC/LL, DLL, and IC of both hemispheres. Identification of different voxel groups was aided by the rat brain atlas. SOC/LL refers to a group of voxels that covers parts of the SOC and lateral lemniscus.
Mentions: Regions of interest (ROIs) were also drawn around the cochlear nucleus, superior olivary complex/lateral lemniscus (a group of voxels that borders the SOC and LL), dorsal lateral lemniscus, and inferior colliculus in each hemisphere using the rat brain atlas [34] as a guide. The precise borders of the ROIs, refer to Fig. 2, were set to include only voxels with r >0.22 and in clusters of three voxels (Stimulate 6.0, University of Minnesota, USA). ROIs were drawn for each animal. For ROIs, BOLD signal ratios were computed by dividing the average BOLD signal of the left hemisphere ROI by that of the corresponding right hemisphere ROI.

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