Increased activity in frontal motor cortex compensates impaired speech perception in older adults.

Yi Du,Cheryl L Grady,Claude Alain,Bradley R Buchsbaum

doi:10.1038/ncomms12241

Abstract

Understanding speech in noisy environments is challenging, especially for seniors. Although evidence suggests that older adults increasingly recruit prefrontal cortices to offset reduced periphery and central auditory processing, the brain mechanisms underlying such compensation remain elusive. Here we show that relative to young adults, older adults show higher activation of frontal speech motor areas as measured by functional MRI during a syllable identification task at varying signal-to-noise ratios. This increased activity correlates with improved speech discrimination performance in older adults. Multivoxel pattern classification reveals that despite an overall phoneme dedifferentiation, older adults show greater specificity of phoneme representations in frontal articulatory regions than auditory regions. Moreover, older adults with stronger frontal activity have higher phoneme specificity in frontal and auditory regions. Thus, preserved phoneme specificity and upregulation of activity in speech motor regions provide a means of compensation in older adults for decoding impoverished speech representations in adverse listening conditions.

Highlights

Understanding speech in noisy environments is challenging, especially for seniors
In a recent functional magnetic resonance imaging study in young adults, we found greater specificity of phoneme representations, as measured by multivoxel pattern analysis (MVPA), in left PMv and Broca’s area than in bilateral auditory cortices during syllable identification with high background noise[14]
The increased activity in speech motor regions could reflect compensation that directly improved phoneme specificity in speech-relevant regions via sensorimotor integration, or a more general increased demand on cognitive processes, such as attention, verbal working memory and categorical judgment. To distinguish between these two possibilities, we investigated the relationships between the mean activity at noise masking conditions ( À 12 to 8 dB SNRs) in the left pars opercularis (POp) spherical ROI and average phoneme specificity across those SNRs in four core regions of the sensorimotor integration network

Summary

Introduction

Understanding speech in noisy environments is challenging, especially for seniors. evidence suggests that older adults increasingly recruit prefrontal cortices to offset reduced periphery and central auditory processing, the brain mechanisms underlying such compensation remain elusive. In a recent functional magnetic resonance imaging (fMRI) study in young adults, we found greater specificity of phoneme representations, as measured by multivoxel pattern analysis (MVPA), in left PMv and Broca’s area than in bilateral auditory cortices during syllable identification with high background noise[14]. This finding suggests that phoneme specificity in frontal articulatory regions may provide a means to compensate for impoverished auditory representations through top-down sensorimotor integration. These results provide neural evidence that in older adults increased recruitment of frontal speech motor regions along with maintained specificity of speech motor representations compensate for declined auditory representations of speech in noisy listening circumstances

Methods

Results

Conclusion