Age-Associated Reduction of Asymmetry in Human Central Auditory Function: A 1H-Magnetic Resonance Spectroscopy Study

Xianming Chen,Ping Luo,Cuixia Wang,Yihong Deng,Shiyan Chen,Yonghui Liang,Jianzhong Li

doi:10.1155/2013/735290

Xianming Chen, Ping Luo + Show 5 more

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https://doi.org/10.1155/2013/735290

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Abstract

The aim of this study was to investigate the effects of age on hemispheric asymmetry in the auditory cortex after pure tone stimulation. Ten young and 8 older healthy volunteers took part in this study. Two-dimensional multivoxel 1H-magnetic resonance spectroscopy scans were performed before and after stimulation. The ratios of N-acetylaspartate (NAA), glutamate/glutamine (Glx), and γ-amino butyric acid (GABA) to creatine (Cr) were determined and compared between the two groups. The distribution of metabolites between the left and right auditory cortex was also determined. Before stimulation, left and right side NAA/Cr and right side GABA/Cr were significantly lower, whereas right side Glx/Cr was significantly higher in the older group compared with the young group. After stimulation, left and right side NAA/Cr and GABA/Cr were significantly lower, whereas left side Glx/Cr was significantly higher in the older group compared with the young group. There was obvious asymmetry in right side Glx/Cr and left side GABA/Cr after stimulation in young group, but not in older group. In summary, there is marked hemispheric asymmetry in auditory cortical metabolites following pure tone stimulation in young, but not older adults. This reduced asymmetry in older adults may at least in part underlie the speech perception difficulties/presbycusis experienced by aging adults.

Highlights

Hemispheric lateralization, known as hemispheric asymmetry, refers to the structural or morphological differences between the right and left hemispheres, as well as the differences in the information processing capacity between the hemispheres [1]
Left and right side NAA/Cr and right side GABA/Cr were significantly lower, whereas right side Glx/Cr was significantly higher in the older group compared with the young group
We found that GABA/Cr was significantly higher in the left auditory cortex after stimulation in both groups

Summary

Introduction

Hemispheric lateralization, known as hemispheric asymmetry, refers to the structural or morphological differences between the right and left hemispheres, as well as the differences in the information processing capacity between the hemispheres [1]. Dichotic listening test findings indicate that people hear verbal sounds, such as syllables or words, more precisely in the right ear than in the left ear. This is known as the right ear or left hemisphere advantage [2]. People perceive nonverbal sounds, such as ambient noise and composite sound, more accurately in the left ear than in the right ear This is known as the left ear or right hemisphere advantage [2]. Morphological and metabolic changes in the auditory cortex may mediate the asymmetry of auditory center function, thereby affecting the analysis, integration, and perception of sound information. Factors that may affect the morphology and function of the auditory center, leading to remodeling and repeated remodeling, include aging, acquired learning (music and sign language), and hearing loss [10,11,12,13,14,15,16]

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