Many older listeners have difficulty understanding speech in noise, when cues to speech-sound identity are less redundant. The amplitude envelope of speech fluctuates dramatically over time, and features such as the rate of amplitude change at onsets (attack) and offsets (decay) signal critical information about the identity of speech sounds. Aging is also thought to be accompanied by increases in cortical excitability, which may differentially alter sensitivity to envelope dynamics. Here, we

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... corded electroencephalography in younger and older human adults (of both sexes) to investigate how aging affects neural synchronization to 4-Hz amplitude-modulated noises with different envelope shapes (ramped: slow attack & sharp decay; damped: sharp attack & slow decay). We observed that subcortical responses did not differ between age groups, whereas older compared to younger adults exhibited larger cortical responses to sound onsets, consistent with an increase in auditory cortical excitability. Older adults showed increased neural synchronization when the envelope shape was damped compared to ramped, whereas younger participants showed the opposite pattern. Furthermore, the response shape of synchronized neural activity was more sinusoidal in younger individuals, whereas synchronized activity in older adults was less sinusoidal and more peaked. The current results suggest that age-related changes in the excitability of auditory cortex alter responses to envelope dynamics, and this may be part of the reason why older adults experience difficulty understanding speech in noise.