Abstract
Learning of new auditory stimuli often requires repetitive exposure to the stimulus. Fast and implicit learning of sounds presented at random times enables efficient auditory perception. However, it is unclear how such sensory encoding is processed on a neural level. We investigated neural responses that are developed from a passive, repetitive exposure to a specific sound in the auditory cortex of anesthetized rats, using electrocorticography. We presented a series of random sequences that are generated afresh each time, except for a specific reference sequence that remains constant and re-appears at random times across trials. We compared induced activity amplitudes between reference and fresh sequences. Neural responses from both primary and non-primary auditory cortical regions showed significantly decreased induced activity amplitudes for reference sequences compared to fresh sequences, especially in the beta band. This is the first study showing that neural correlates of auditory pattern learning can be evoked even in anesthetized, passive listening animal models.
Highlights
Sensory perception requires correctly recognizing incoming sensory stimuli by extracting relevant information from memory
We compared neural dynamics of re-occurring sequences with the same acoustic characteristics (RefRS and RefS) and a group of other sequences that were presented only once (RS and S), by computing induced activity amplitude of neural signals recorded from primary (A1) and higher-order auditory cortex
We observed decreased induced activity amplitude throughout the stimulus sequence for RefRS and RefS compared to RS and S, mainly in the beta band, both for A1 and non-A1 channel clusters, but only for dynamic random chords (DRCs) stimulus sequences which contain more salient acoustical features compared to white noise (WN)
Summary
Sensory perception requires correctly recognizing incoming sensory stimuli by extracting relevant information from memory. Unbeknownst to them, one specific noise sample would re-occur occasionally, and even though the subjects were unaware of this, they showed fast, selective improvement in processing the frozen “reference” stimulus, which implies rapid and robust memorization of Neural Correlates of Auditory Learning random features of complex sounds Such behavioral improvement for the re-occurring sound was supported by increased inter-trial coherence of brain responses for the reoccurring stimulus compared to other random stimuli measured by subsequent EEG and MEG studies in humans (Luo et al, 2013; Andrillon et al, 2015). Increases in neural coherence could even be observed when the human subjects were in Rapid Eye Movement (REM) or light non-REM sleep during the experiment (Andrillon et al, 2017), suggesting that a neural index related to learning new sounds can be traced even following passive exposure While these findings provided insights into the neural correlates of implicit learning of new auditory stimuli, further investigations using invasive measurements will be needed to understand the underlying mechanisms. The present study aimed at investigating neural responses shaped by passively presented re-occurring sounds in the auditory cortex using rats as an animal model
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