Auditory training alters the cortical representation of both learned and task irrelevant sound features

Abstract

AbstractAuditory learning is supported by long-term changes in the neural processing of sound. We mapped neural sensitivity to timbre, pitch and location in animals trained to discriminate the identity of artificial vowels based on their spectral timbre in a two-alternative forced choice (T2AFC, n=3, female ferrets) or to detect changes in fundamental frequency or timbre of repeating artificial vowels in a go/no-go task (n=2 female ferrets). Neural responses were recorded under anaesthesia in two primary cortical fields and two tonotopically organised non-primary fields. Responses were compared these data to that of naïve control animals. We observed that in both groups of trained animals the overall sensitivity to sound timbre was reduced across three cortical fields but enhanced in non-primary field PSF. Neural responses in trained animals were able to discriminate vowels that differed in either their first or second formant frequency unlike control animals whose sensitivity was mostly driven by changes in the second formant. Neural responses in the T2AFC animals, who were required to generalise across pitch when discriminating timbre, became less modulated by fundamental frequency, while those in the go/no-go animals were unchanged relative to controls. Finally, both trained groups showed increased spatial sensitivity and altered tuning. Trained animals showed an enhanced representation of the midline, where the speaker was located in the experimental chamber. Overall, these results demonstrate training elicited widespread changes in the way in which auditory cortical neurons represent complex sounds with changes in how both task relevant and task-irrelevant features were represented.