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Young zebra finch songbirds typically learn their father's (tutor) song which serves as a template for the development of their own song. Some birds imitate their tutor’s song with great success (good learners) whereas others fail to copy key components of the model song (poor learners). NCM (caudomedial Nidopallium), a secondary auditory region in the avian brain, is thought to contain (part of) the substrate for the neural representation of tutor song memory. Good learners exhibit greater left-hemispheric dominance in this region upon re-exposure to tutor song, indicating a role for the left NCM in the song learning process. It has been shown that a significant portion of cells in NCM are inhibitory - they impede rather than promote cell activity. Furthermore, inhibition plays a critical role in song learning in brain areas involved in producing the song. Given the importance of inhibition in the song learning process, the current study investigates whether individual differences in learning outcomes can be explained by the distribution of inhibitory neurons within the auditory region NCM that contains (part of) the substrate for the neural representation of tutor song memory. We measured the densities of distinct inhibitory subpopulations (defined by their expression of the calcium-binding proteins Calbindin, Calretinin, or Parvalbumin) in NCM of juvenile zebra finches. We found that good learners have fewer inhibitory neurons in the left medial NCM than poor learners. Moreover, it is a decrease in the Calbindin expressing subpopulation in the left hemisphere of the good learners that drives this overall difference. These findings not only identify a specific inhibitory subpopulation (Calbindin expressing neurons) that relates to song learning, but also emphasize both the role of inhibition in auditory memory formation and the dominance of the left hemisphere in the song learning process.
Available for download on Tuesday, April 25, 2023