Birdsong: is it music to their ears?

Abstract

Since the time of Darwin, biologists have wondered whether birdsong and music may serve similar purposes or have the same evolutionary precursors. Most attempts to compare song with music have focused on the qualities of the sounds themselves, such as melody and rhythm. Song is a signal, however, and as such its meaning is tied inextricably to the response of the receiver. Imaging studies in humans have revealed that hearing music induces neural responses in the mesolimbic reward pathway. In this study, we tested whether the homologous pathway responds in songbirds exposed to conspecific song. We played male song to laboratory-housed white-throated sparrows, and immunolabeled the immediate early gene product Egr-1 in each region of the reward pathway that has a clear or putative homologue in humans. We found that the responses, and how well they mirrored those of humans listening to music, depended on sex and endocrine state. In females with breeding-typical plasma levels of estradiol, all of the regions of the mesolimbic reward pathway that respond to music in humans responded to song. In males, we saw responses in the amygdala but not the nucleus accumbens - similar to the pattern reported in humans listening to unpleasant music. The shared responses in the evolutionarily ancient mesolimbic reward system suggest that birdsong and music engage the same neuroaffective mechanisms in the intended listeners.

Keywords: Egr-1; mesolimbic reward system; music; reward; song; songbird.

Figure 1

Example of song-induced Egr-1 immunoreactivity. Photomicrographs show the caudolateral nidopallium (putative homologue of the prefrontal cortex; see Table 1) in estradiol-treated female white-throated sparrows listening to synthetic tones (A) or conspecific song (B). These examples depict the expression levels closest to each within-group median. Scale bar = 50 μm.

Figure 2

Normalized Egr-1 responses in the mesolimbic reward system in (A) female and (B) male white-throated sparrows listening to conspecific male song. For each region, cell density values were divided by the mean tone (control) value to create a normalized Egr-1 fold-induction scale (Jarvis et al., 1995). Values greater than 1 indicate that the mean response to song was greater than the mean response to tones for that region. In the E2-treated females, the response to song was significantly higher than the response to tones in each ROI measured. In the males, we observed selective Egr-1 responses only in TnA. *Significantly greater Egr-1 induction to song than tones; ^† Significant interaction between hormone treatment and auditory stimulus.