Early experience improves neural discrimination/recognition of natural complex sounds

Abstract

In natural environments, behaviorally relevant complex sounds are often produced with “speaker” variability and contaminated with environmental noises. To efficiently discriminate/recognize natural complex sounds, the auditory system has to tune to defining acoustic features and filter out random, meaningless features. In humans, for example, efficient speech recognition is achieved by enhancing perceptual contrast for native speech sounds, as well as reducing perceptual contrast for non-native speech sounds. The neural mechanisms underlying this perceptual transformation are still not well understood. We exposed juvenile rats to heterospecific vocalizations recorded in a natural environment, and subsequently examined their cortical complex sound representations. Cortical neurons became more responsive to dynamic and complex features of the complex sounds. In addition, more neurons were involved in representing the whole set of complex sounds, but fewer neurons actually responded to each individual sound. Cortical responses to different renderings of the same song motif were more similar, and responses to sounds of different motifs became more distinctive, indicating that cortical neurons were more selective to the defining features of the experienced sounds. These effects lead to better neural discrimination/recognition of the experienced complex sounds.