Auditory Training Alters the Cortical Representation of Complex Sounds

Auditory learning is supported by long-term changes in the neural processing of sound. We examined these task-depend changes in the auditory cortex by mapping neural sensitivity to timbre, pitch, and location cues in cues in trained (n = 5) and untrained control female ferrets (n = 5). Trained animals either identified vowels in a two-alternative forced choice task (n = 3) or discriminated when a repeating vowel changed in identity or pitch (n = 2). Neural responses were recorded under anesthesia in two primary auditory cortical fields and two tonotopically organized nonprimary fields. In trained animals, the overall sensitivity to sound timbre was reduced across three cortical fields compared with control animals, but maintained in a nonprimary field (the posterior pseudosylvian field). While training did not increase sensitivity to timbre across the auditory cortex, it did change the way in which neurons integrated spectral information, with neural responses in trained animals increasing their sensitivity to first and second formant frequencies, whereas in control animals cortical sensitivity to spectral timbre depended mostly on the second formant. Animals trained on timbre identification were required to generalize across pitch when discriminating timbre, and their neurons became less modulated by fundamental frequency relative to control animals. Finally, both trained groups showed increased spatial sensitivity and an enhanced response to sound source locations close to the midline, where the loudspeaker was located in the training chamber. These results demonstrate that training elicited widespread alterations in the cortical representation of complex sounds.