Age-related processing delay reveals cause of apparent sensory excitability following auditory stimulation

Abstract

When background auditory events lead to enhanced auditory event-related potentials (ERPs) for closely following sounds, this is generally interpreted as a transient increase in the responsiveness of the auditory system. We measured ERPs elicited by irrelevant probes (gaps in a continuous tone) at several time-points following rare auditory events (pitch glides) in younger and older adults, who watched movies during stimulation. Fitting previous results, in younger adults, gaps elicited increasing N1 auditory ERPs with decreasing glide-gap separation. N1 increase was paralleled by an ERP decrease in the P2 interval. In older adults, only a glide-gap separation dependent P2 decrease, but no N1-effect was observable. This ERP pattern was likely caused by a fronto-central negative waveform, which was delayed in the older adult group, thus overlapping N1 and P2 in the younger, but overlapping only P2 in the older adult group. Because the waveform exhibited a polarity reversal at the mastoids, it was identified as a mismatch negativity (MMN). This interpretation also fits previous studies showing that gap-related MMN is delayed in older adults, reflecting an age-related deterioration of fine temporal auditory resolution. These results provide a plausible alternative explanation for the ERP enhancement for sounds following background auditory events.

Intensity and inter‐stimulus‐interval effects on human middle‐ and long‐latency auditory evoked potentials in an unpredictable auditory context

“…This phenomenon, referred as N1 facilitation, has been hypothesized as caused by several factors: (1) an accelerated decay of inhibitory over excitatory postsynaptic potentials at high (<200 ms) stimulation rates (Loveless et al, 1989); (2) avoiding a latent inhibitory feedback from N1 generators if stimulus is presented before inhibition takes place (Sable et al, 2004); (3) a separate neural component with a time course overlapping N1 and P2 that is modulated exclusively by very short ISI (Wang et al, 2008). Some evidence supports this overlapping component may be Mismatch Negativity (Volosin et al, 2017(Volosin et al, , 2021. Our results best fit the third hypothesis, as P2 in addition to N1 followed a different pattern of results under our shortest ISI, reduced more prominently than for other ISIs.…”