Abstract
The auditory cortex integrates auditory information over time to obtain neural representations of sound events, the time scale of which critically affects perception. This work investigated the species differences in the time scale of integration by comparing humans and monkeys regarding how their scalp-recorded cortical auditory evoked potentials (CAEPs) decrease in amplitude as stimulus duration is shortened from 100 ms (or longer) to 2 ms. Cortical circuits tuned to processing sounds at short time scales would continue to produce large CAEPs to brief sounds whereas those tuned to longer time scales would produce diminished responses. Four peaks were identified in the CAEPs and labeled P1, N1, P2, and N2 in humans and mP1, mN1, mP2, and mN2 in monkeys. In humans, the N1 diminished in amplitude as sound duration was decreased, consistent with the previously described temporal integration window of N1 (>50 ms). In macaques, by contrast, the mN1 was unaffected by sound duration, and it was clearly elicited by even the briefest sounds. Brief sounds also elicited significant mN2 in the macaque, but not the human N2. Regarding earlier latencies, both P1 (humans) and mP1 (macaques) were elicited at their full amplitudes even by the briefest sounds. These findings suggest an elongation of the time scale of late stages of human auditory cortical processing, as reflected by N1/mN1 and later CAEP components. Longer time scales of integration would allow neural representations of complex auditory features that characterize speech and music.
Highlights
Auditory information is integrated over time for obtaining neural representations of auditory events in the brain (Heil and Neubauer, 2001; Lerner et al, 2011; Farbood et al, 2015)
Temporal integration occurs at each level of auditory processing, from peripheral to central, and the time scale of neural representations of continuously incoming sounds generally becomes longer at higher levels of sensory processing, reflecting the accumulation of information over time (Lerner et al, 2011; Hasson et al, 2015)
The human and macaque cortical auditory evoked potentials (CAEPs) had the same number of peaks with matched polarities, the latencies were overall shorter in the macaque
Summary
Auditory information is integrated over time for obtaining neural representations of auditory events in the brain (Heil and Neubauer, 2001; Lerner et al, 2011; Farbood et al, 2015). Temporal integration occurs at each level of auditory processing, from peripheral to central, and the time scale of neural representations of continuously incoming sounds generally becomes longer at higher levels of sensory processing, reflecting the accumulation of information over time (Lerner et al, 2011; Hasson et al, 2015). Regarding the final stages of auditory processing that are directly relevant to the perception and cognition of sounds, the time scale of auditory cortical functions is implicitly assumed to be similar across human and non-human primate species. This assumption, has never been explicitly tested to our knowledge. The macaque homologs of human cortical auditory evoked potentials (CAEPs) have shorter latencies compared with the human CAEP (Fishman et al, 2000b; Itoh et al, 2015), which strongly suggests shorter time scales of auditory cortical processing in the macaque cortex
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