Abstract
Speech understanding problems are highly prevalent in the aging population, even when hearing sensitivity is clinically normal. These difficulties are attributed to changes in central temporal processing with age and can potentially be captured by age-related changes in neural generators. The aim of this study is to investigate age-related changes in a wide range of neural generators during temporal processing in middle-aged and older persons with normal audiometric thresholds. A minimum-norm imaging technique is employed to reconstruct cortical and subcortical neural generators of temporal processing for different acoustic modulations. The results indicate that for relatively slow modulations (<50 Hz), the response strength of neural sources is higher in older adults than in younger ones, while the phase-locking does not change. For faster modulations (80 Hz), both the response strength and the phase-locking of neural sources are reduced in older adults compared to younger ones. These age-related changes in temporal envelope processing of slow and fast acoustic modulations are possibly due to loss of functional inhibition, which is accompanied by aging. Both cortical (primary and non-primary) and subcortical neural generators demonstrate similar age-related changes in response strength and phase-locking. Hemispheric asymmetry is also altered in older adults compared to younger ones. Alterations depend on the modulation frequency and side of stimulation. The current findings at source level could have important implications for the understanding of age-related changes in auditory temporal processing and for developing advanced rehabilitation strategies to address speech understanding difficulties in the aging population.
Highlights
Speech understanding becomes increasingly challenging with age
The present study investigated the effect of age on the neural generators involved in the temporal envelope processing in adults with normal audiometric thresholds
Age-related changes were observed for response strength, phase coherence, and hemispheric asymmetry
Summary
Speech understanding becomes increasingly challenging with age. Many middle-aged and older people experience difficulties following conversations, especially in noisy environments or when multiple speakers are talking simultaneously. While aging is often accompanied by loss of hearing sensitivity in the high frequencies, these difficulties occur even with normal hearing sensitivity most probably due to age-related changes in central temporal processing (e.g., Presacco et al, 2015, 2019; Du et al, 2016; Goossens et al, 2016; Roque et al, 2019). Responses to sound envelopes in the central auditory system alter with progressing age (Walton et al, 2002; Presacco et al, 2015, 2019; Goossens et al, 2016; Parthasarathy et al, 2019). In order to gain a better understanding of age-related changes in central temporal processing, envelope encoding, it is of great interest to disentangling the effect of aging and hearing loss via recruiting older participants who are relatively free of hearing loss
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