Neural basis of song perception in songbirds

Abstract

Brain nuclei of the song control system involved in song perception change in size between seasons. It has been hypothesized that seasonal regression of song nuclei may impair song discrimination (Cynx and Nottebohm, 1992). We predicted that song sparrows (Melospiza melodia) with regressed song systems would have greater difficulty in discriminating between similar songs. Birds did not differ in their ability to learn to discriminate between shared song types.Phosphorylation of cAMP response element binding protein (pCREB) plays a role in memory formation. Playback of conspecific song to zebra finches (Taeniopygia guttata) induced pCREB in HVC (Sakaguchi 1999). We played recordings of either the novel or familiar songs to wild male song sparrows. HVC of birds exposed to stranger song showed higher levels of pCREB relative to surrounding tissue. This suggests that pCREB levels in HVC may be related to learning song memories in birds.Female song recognition provides an opportunity to investigate the role of the song control system in recognition. We attempted to map auditory responses based on the phosphorylation of CREB in HVC and CMM in response to novel or familiar song. The females did not respond to the playback and likely did not form long term memories of the song as pCREB levels remained at basal levels. pCREB increased in two birds but it was unclear whether the increase was related to their behavioral response or experience with the song.The anterior forebrain pathway (AFP) is involved in song learning and perception. Lesions to the AFP reduce a songbird's ability to make discriminations in operant conditioning tasks (Scharff et al., 1998; Burt et al., 2000). We investigated whether the AFP plays a role in wild male song sparrows that must discriminate neighbor and stranger songs for successful territory defense. We predicted that lesions to the AFP in would impair bird's ability to discriminate songs. Birds did not discriminate between songs following lesions to the anteromedial forebrain. The inaccuracy of the lesion sites makes the result difficult to interpret. The lesions may have damaged axons projecting from HVC to Area X.