Juvenile songbirds memorize tutor songs during the sensory period, and then gradually match their immature songs to memorized tutor songs using auditory feedback. To accomplish this sensorimotor task, tutor song memory should be represented in the brain. A growing body of evidence shows that tutor song memory is stored in the songbird auditory cortex. To date, however, it is unclear how early auditory experience alters song selectivity of auditory neurons and how the memory of tutor song is archived. Here, we examine how auditory experience during the sensory period changes the song selectivity of auditory neurons in the caudomedial nidopallium (NCM, corresponding to the mammalian higher-level auditory cortex). We recorded single-unit activity from the NCM of freely moving juvenile zebra finches before and after tutor song exposure. To evaluate song selectivity, a variety of behaviorally relevant sound stimuli were presented from a speaker during neural recording.
We found that tutor song-selective neurons emerged following exposure to songs from a live tutor. Before tutoring, auditory responses of NCM neurons showed no preference for specific songs of any origin. However, after more than 4 days of exposure to a live tutor, a group of 19 neurons (among 246) showed highly selective responses to tutor songs. We also found another group of 12 neurons that selectively responded to developing birds' own songs, and 5 other neurons that selectively responded to both tutor songs and the birds' own songs. These results suggest that auditory experience during the sensory period modulates auditory neuron circuitry in the higher-level auditory cortex of juvenile songbirds.