Fig 1.
Neural circuits for birdsong learning and production.
The canonical circuitry underlying song learning and control (“song system”) is parsed into the vocal motor pathway (red and orange boxes), which includes HVC (used as a proper name), RA, and hindbrain areas that contain vocal motor and respiratory neurons, and the anterior forebrain pathway (blue boxes), which includes the vocal basal ganglia nucleus Area X, DLM, and LMAN. HVC (which is thought to be analogous to the premotor cortex in mammals) and RA (which is thought to be analogous to parts of the primary motor cortex [22,30]) are critical for adult song production and implicated in species variation in song. DLM, medial portion of the dorsolateral thalamic nucleus; LMAN, lateral magnocellular nucleus of the anterior nidopallium; RA, robust nucleus of the arcopallium.
Fig 2.
Cross-fostering and species hybrids lend insight into genetic constraints on and mechanisms of learning.
(A) Cross-fostering young songbirds with a different songbird species can provide information on both the degree of plasticity in learning (based on how much song juvenile birds copy from their heterospecific tutor) and constraints on learning (based on how much of their species-typical song juvenile birds retain). In this example, which illustrates the experiment by Wang and colleagues, birds are removed from the nest and then tutored with the song of a different species played out from a speaker. In the illustrated song, spectrograms and colored bars represent the song’s spectral information, and the background highlights temporal information. A number of studies in songbirds demonstrate that cross-fostered birds learn the spectral properties of heterospecific songs (illustrated by the color and height of the bars) but retain several temporal properties of their own species (illustrated by the background color and spacing between elements). (B) Studies of song learning in species hybrids also indicate genetic contributions to learning. First filial (F1) hybrids (generated using both directions of hybridizations) vary in their allele-specific expression ratio toward each parent species. This variation may lead to differences in behavior that can be correlated with genetic markers and gene expression.