Abstract
As people age, speech perception problems become highly prevalent, especially in noisy situations. In addition to peripheral hearing and cognition, temporal processing plays a key role in speech perception. Temporal processing of speech features is mediated by synchronized activity of neural oscillations in the central auditory system. Previous studies indicate that both the degree and hemispheric lateralization of synchronized neural activity relate to speech perception performance. Based on these results, we hypothesize that impaired speech perception in older persons may, in part, originate from deviances in neural synchronization. In this study, auditory steady-state responses that reflect synchronized activity of theta, beta, low and high gamma oscillations (i.e., 4, 20, 40, and 80 Hz ASSR, respectively) were recorded in young, middle-aged, and older persons. As all participants had normal audiometric thresholds and were screened for (mild) cognitive impairment, differences in synchronized neural activity across the three age groups were likely to be attributed to age. Our data yield novel findings regarding theta and high gamma oscillations in the aging auditory system. At an older age, synchronized activity of theta oscillations is increased, whereas high gamma synchronization is decreased. In contrast to young persons who exhibit a right hemispheric dominance for processing of high gamma range modulations, older adults show a symmetrical processing pattern. These age-related changes in neural synchronization may very well underlie the speech perception problems in aging persons.
Highlights
With advancing age, people experience greater difficulty following conversations, especially in the presence of background noise and/or when multiple speakers are talking (Pichora-Fuller and Souza, 2003)
The size of the auditory steady-state response (ASSR) reflects the degree to which neural oscillatory activity synchronizes to acoustic modulations that coincide with the characteristic frequency of the oscillations
Bonferroni posthoc testing indicated that older listeners exhibited a higher 4 Hz neural signal-tonoise ratio (SNR) than young subjects, irrespective of the side of stimulation (L: mean difference (MD) = 3.13 dB, p = 0.052; R: MD = 3.71 dB, p = 0.017; BI: MD = 3.49 dB, p = 0.005)
Summary
People experience greater difficulty following conversations, especially in the presence of background noise and/or when multiple speakers are talking (Pichora-Fuller and Souza, 2003) This impaired speech perception can be attributed to age-related peripheral hearing loss (Abel et al, 2000) as well as to declining cognitive abilities (Van der Linden et al, 1999) and changes in central temporal processing (Martin and Jerger, 2005). The size of the ASSR reflects the degree to which neural oscillatory activity synchronizes to acoustic modulations that coincide with the characteristic frequency of the oscillations. The size of the 40 Hz ASSR reflects the degree of synchronized activity of low gamma oscillations in response to 40 Hz acoustic modulations
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