The Effect of Aging and the High-Frequency Auditory Threshold on Speech-Evoked Mismatch Negativity in a Noisy...

Mismatch negativity (MMN) has been widely used to study the function of central auditory processing in the elderly. However, current research has not yet considered the effect of noise and high-frequency hearing threshold on MMN in the elderly. The aim of this study was to evaluate the effect of aging and high-frequency hearing loss on speech-related MMN in noisy backgrounds. Additionally, the possible mechanisms of central auditory processing dysfunction in the elderly were investigated. Fifty people aged 61-80 (70 ± 5.8) years were recruited for this study. They were divided into a 61- to 70-year-old group and a 71- to 80-year-old group. Fifty younger adults aged 21-40 (31 ± 5.3) years were recruited as healthy controls. Pure-tone hearing thresholds were recorded. A speech discrimination score (SDS) and a speech-evoked MMN under white noise with a bandwidth from 125 to 8,000 Hz background condition were recorded. The relationships between SDS and MMN latency and amplitude were analyzed. The effects of age and binaural 2,000-, 4,000- and 8,000-Hz pure-tone hearing thresholds on MMN latency and amplitude were analyzed. We found that the hearing thresholds of 2,000, 4,000 and 8,000 Hz in the 61- to 70-year-old and 71- to 80-year-old groups were higher than those in the control group. The SDS in a noisy background in the 61- to 70-year-old and 71- to 80-year-old groups were lower than those in the control group. Speech-evoked MMN latency was longer in the 61- to 70-year-old and in the 71- to 80-year-old groups than in the control group (215.8 ± 14.2 ms). SDS and speech-evoked MMN latency were negatively correlated. Age and speech-evoked MMN latency were positively correlated, as were the binaural 4,000- to 8,000-Hz pure-tone hearing thresholds and speech-evoked MMN. This study suggests that in elderly subjects, the function of preattentive central auditory processing changes. Additionally, increasing age and high-frequency hearing thresholds create a synergy in neurons that is weakened in the MMN time window, which may be a cause of central auditory processing disorders in elderly subjects in noisy background conditions.