The effects of aging on neural signatures of temporal regularity processing in sounds

Abstract

Sensitivity to temporal regularity (e.g., amplitude modulation) is crucial for speech perception.Degradation of the auditory periphery due to aging and hearing loss may lead to an increased response gain in auditory cortex, with potential consequences for the processing of temporal regularities. We used electroencephalography recorded from younger (18-33 years) and older (55-80 years) adults to investigate how aging affects neural gain and the neural sensitivity to amplitude modulation in sounds.Aging was associated with reduced adaptation in auditory cortex, suggesting an age-related gain increase. Consistently, neural synchronization in auditory cortex to a 4-Hz amplitude modulation of a narrow-band noise was enhanced in ~30% of older individuals. Despite enhanced responsivity in auditory cortex, sustained neural activity (likely involving auditory and higher-order brain regions) in response to amplitude modulation was absent in older people. Hence, aging may lead to an overresponsivity to amplitude modulation in auditory cortex, but to a diminished regularity representation in higher-order areas.

Sound level context modulates neural activity in the human brainstem

“…Adaptation to sound-level context or other properties of the acoustic environment -often referred to as adaptation to stimulus statistics 15,16,18 -requires that neurons represent stimulation history across several stimuli. For Experiment I and Supplementary Experiments A and B, we adapted experimental paradigms from our previous work on longer-term adaptation in the human auditory cortex 42,43 to investigate the extent to which stimulation history is reflected in adaptation of human brainstem responses. We observed that the Wave V of the auditory evoked potential -originating from the brainstem 41,[44][45][46][47] -peaked later when more clicks occurred within a preceding time window ("decelerating" sequence) compared to fewer clicks ("accelerating" sequence), despite an identical interval directly preceding each target click and identical sound levels (Experiments I and Supplementary Experiment A; Figures 1 and S1).…”

“…A prerequisite for adaptation to sound-level context is the capacity of neurons to represent the sound history over several stimuli in their activity patterns. To investigate whether the human brainstem is sensitive to sound history, we adapted a paradigm that has been successfully utilized to investigate adaptation of the human auditory cortex 42,43 . In Experiment I, normal-hearing younger adults (N=17) listened to click sequences presented at 60 dB sensation level (SL) that continuously "accelerated" and "decelerated": the click onset-to-onset interval decreased logarithmically from 60 ms to 10 ms and then increased back to 60 ms (Figure 1A).…”

“…Acoustic stimulation. Participants listened to six blocks of stimulation (each about 8 min long) that comprised click-train stimuli, in which the onset-to-onset interval of clicks changed from 60 ms to 10 ms (in 7 logarithmically-spaced steps) and back from 10 ms to 60 ms (in 7 logarithmically-spaced steps), creating an accelerating-decelerating stimulation cycle (Figure 1A; see also 42,43 ). Across the six blocks, participants listened to 7,200 accelerating-decelerating stimulation cycles.…”