Figure 1.

Schematic of song-control pathways in adult zebra finches. Song-control circuits include the HVC-RA vocal motor pathway in adult birds (boxes shaded gray) and a cortico-basal ganglia-thalamo circuit that is necessary for vocal plasticity (LMAN→Area X→DLM; boxes, gray outline). One population of projection neurons in HVC (HVC_RA) sends axonal projections to RA in motor cortex, which in turn drives activity in hypoglossal motor neurons (nXIIts) and respiratory areas in the hindbrain to produce vocal output. Boxes with dashed lines indicate cortical regions with robust auditory responses to vocal sounds that provide input to HVC. The box titled “auditory cortex” includes the thalamorecipient region of primary auditory cortex and adjacent regions, known collectively as the “Field L” complex in avian brain (Wang et al., 2010). Av is a subregion contained within CM (Akutagawa and Konishi, 2010). It should be noted that both NIf and CM/Av may be at least partly sensorimotor in nature (Cardin et al., 2005; Bauer et al., 2008). The term “cortex” is used here generically in the sense described by Reiner et al. (2004; see Discussion). Area X, Area X of the medial striatum (which includes both striatal and pallidal components); Av, nucleus avalanche; CM, caudal mesopallium; DLM, medial dorsolateral nucleus of the thalamus; HVC, high vocal center; LMAN, lateral magnocellular nucleus of the anterior nidopallium; MMAN, medial magnocellular nucleus of the anterior nidopallium; NIf, nucleus interface of the nidopallium; nXIIts, tracheosyringeal portion of the hypoglossal nucleus; RA, robust nucleus of the arcopallium; Uva, uvaeform nucleus of the thalamus.