Analysis of the mechanism of neural substrates for song and vocal control system in the forebrain nuclei (HVc.RA.X) in the song bird.

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In this study conducted with two graduate students I used adult male Bengalese finches and chicks of Japanese quails. Male birds of age-limited song learning species develop their full song repertoires in the first year of life. For this type of song learner, once song is "crystallized" in adulthood, it is highly stereotyped and stable over time. Traditionally, it has been believed that age-limited song learners do not depend upon auditory feedback for the maintenance of adult song. I surgically deafened adult males by bilateral cochlear removal and recorded song weekly for 20 weeks following the surgery. Results show that song degraded significantly within about 1 week of surgery. Song deficits after deafening included a marked decrease in syllable sequence and stereotype syllables of high fundamental frequency or high frequency modulation within song bouts. Occurrences of new syllables with low fundamental frequency or low frequency modulation within song bouts appeared within 2 weeks of deafening and increased over time. Song of next 10 weeks after deafening kept stable with different pattern from the pre-surgical song of the bird. This indicates that auditory feedback is necessary for song maintenance in Bengalese finches of age-limited song learners.Japanese quail chicks which are socially isolated form other individuals produce distress calls at a high rate. Chronical subcutaneous implantation of testosterone induced the chick crowing which has similar acoustical structural characteristics to male adult crowing. At day 6 after testosterone implantation, the chicks produced the chick crowing similar to adult crow with a trill structure by electrical stimulation. The area in brainstem of chicks that exhibit two different kinds of vocal behavior upon electrical stimulation lies in the medial intercollicular nucleus (ICo). This suggests that the medial ICo of chicks has two different functions, production of distress call and chick crowing.