Figure 1. Neuroanatomical overview.

(A) Schematic comparison of avian and human cortico-basal ganglia loops. Left, composite sagittal view of songbird telencephalon highlights song control nuclei. Auditory input (not shown) enters the song circuit at cortical HVC, the neurons of which contribute to 2 pathways, the vocal motor pathway (plain arrows) and the anterior forebrain pathway (stippled arrows). The latter includes basal ganglia nucleus area X and rejoins the vocal motor pathway via projections from the cortical lateral magnocellular nucleus of the anterior nidopallium (LMAN) to the robust nucleus of the arcopallium (RA). Middle, songbird cortico-basal ganglia circuitry is further simplified to illustrate song-specialized sub-regions that are embedded within similar brain areas in the human brain (Right). Cortex is in white, basal ganglia dark gray and thalamus light gray. Adapted from Teramitsu et al. (2004)⁴.

(B) Striato-pallidal brain regions that gave rise to the oligoarray data consist of area X and VSP. Left, line drawing of a coronal section through anterior zebra finch brain shows anatomical borders and highlights area X, observable in the Nissl-stained section. Right, bilateral tissue punches of equivalent size were taken from area X (holes) and VSP (circles). Abbreviations: D-Dorsal, HA-Hyperpallium apicale, HD–hyperpallium densocellulare, M–mesopallium, N–nidopallium, R-Rostral, X–song control area X, VSP-ventral striato-pallidum. Adapted from Miller et al. (2008)⁹. See also Figure S1