Relationship between neural phase-locked responses to speech and perception of speech in noise in young and older adults

Auditory phase-locked responses are affected by aging and it has been proposed that this increases the challenges experienced during speech perception in noise (SPiN). However, this proposal lacks direct support. This issue was addressed by measuring speech-evoked phase-locked responses at subcortical (frequency-following responses, FFRs) and cortical (theta-band phase-locking, {theta}-PLV) levels, and studying the relationship between these phase-locked responses and SPiN (word report accuracies of sentences listened to in noise) in adults across a wide age-range (19-75 years old). It was found that: (1) FFR magnitudes declined with age after hearing loss was controlled for; (2) {theta}-PLV increased with age, suggesting cortical hyperexcitability in audition; (3) SPiN correlated positively with FFR magnitudes obtained in quiet and with {theta}-PLV obtained in noise, suggesting that impacts of aging (smaller FFR magnitudes and greater {theta}-PLV) on SPiN differ at subcortical and cortical levels. Thus, the current study provided evidence for different mechanisms at subcortical and cortical levels through which age affects speech-evoked phase-locked activities and SPiN.