Age-related hearing loss is associated with alterations in temporal envelope processing in different neural generators along the auditory pathway

Abstract

People with age-related hearing loss suffer from speech understanding difficulties, even after correcting for differences in hearing audibility. These problems are not only attributed to deficits in audibility but are also associated with changes in central temporal processing. The goal of this study is to obtain an understanding of potential alterations in temporal envelope processing for middle-aged and older persons with and without hearing impairment. The time series of activity of subcortical and cortical neural generators was reconstructed using a minimum-norm imaging technique. This novel technique allows for reconstructing a wide range of neural generators with minimal prior assumptions regarding the number and location of the generators. The results indicated that the response strength and phase coherence of middle-aged participants with hearing impairment (HI) were larger than for normal-hearing (NH) ones. In contrast, for the older participants, a significantly smaller response strength and phase coherence were observed in the participants with HI than the NH ones for most modulation frequencies. Hemispheric asymmetry in the response strength was also altered in middle-aged and older participants with hearing impairment and showed asymmetry toward the right hemisphere. Our brain source analyses show that age-related hearing loss is accompanied by changes in the temporal envelope processing, although the nature of these changes varies with age.

Keywords: EEG; age-related hearing loss (ARHL); auditory steady-state response (ASSR); auditory temporal processing; neural generators.

Figure 1

Median audiometric thresholds (dB HL) of normal-hearing (NH) and hearing-impaired (HI) participants, averaged across both ears. Thresholds are indicated by circles, squares, and triangles for young, middle-aged, and older persons, respectively. Error bars indicate the interquartile range. NH, normal hearing; HI, hearing impaired.

Figure 2

The regions of interest (ROIs) along the auditory pathway. The cortical ROIs are located bilaterally in the left auditory cortex (LAC) and right auditory cortex (RAC). The subcortical ROIs include the left and right medial geniculate body (LMGB, RMGB), the left and right inferior colliculus (LIC, RIC), and the left and right cochlear nucleus (LCN, RCN).

Figure 3

ASSR amplitudes of the neural generators in the auditory cortices and subcortical neural generators in NH and HI participants regardless of the side of stimulation across age and modulation frequency. The circle and triangle symbols indicate the pooled means (i.e., the weighted average of amplitudes across the side of stimulation and the side of generators; number of subjects as weights), and error bars represent the pooled standard deviations (69).

Figure 4

Phase coherence of the neural generators in auditory cortices and subcortical area in NH and HI participants regardless of the side of stimulation across age and modulation frequency. The circle and triangle symbols indicate the pooled means, and error bars represent the pooled standard deviations (69).

Figure 5

Hemispheric lateralization for normal-hearing (NH) and hearing-impaired (HI) listeners (indicated by solid lines and dotted lines, respectively) in different stimulation conditions (indicated by different colors) and different age groups. For 4, 20, and 40 Hz stimuli, the laterality indexes (LIs) were calculated based on the auditory cortex (AC), while for 80 Hz stimuli the LIs were calculated based on the medial geniculate body (MGB). The error bars illustrate the estimated standard deviations using the jackknife method (65).