Fig. 1.

Simplified schematics of the hypothesis that the adult HVC song nucleus contains an asymmetric network that supports travelling waves, whereas the juvenile HVC does not. Parasagittal sections of the HVC (ovoid shapes) are shown. Neuronal cell bodies are represented by circles, with spiking activity indicated by cyan and quiescence by red. Rostrocaudally oriented axons are indicated by black lines. A: in adults, three snapshots in time reveal the asymmetrical activation of the HVC as an activity wave travels in the rostrocaudal axis. B: in contrast, the asymmetrical activation of the juvenile HVC would not be detectable, according to the hypotheses that dynamic network structure is important for the production of learned song and that juveniles lack this structure.