Songbird brain circuitry

This diagram represents a sagittal section (as if you are looking at the right ear, with the beak to the right and the back of the head to the left) of a generalized songbird brain, showing the circuits that are known to be involved in learning and singing a male zebra finch's song.

The song output pathway ( HVc -> RA -> DM -> nXIIts; shown in blue) controls the vocal organ, or syrinx. Lesioning this pathway in adult or in juvenile males affects the song. The axons from the motor neurons in nXIIts form NXIIts, the tracheosyringeal portion of the twelfth cranial nerve.

The subthalamic nucleus Uva receives projections from many areas and then sends axons to the forebrain nuclei NIf and HVc. NIf also sends axons to HVc. The Uva -> NIf -> HVc circuit, shown in green, may be important for defining the sequence of units sung within the song.

The pathway shown in purple is presumed to have a role in coordinating the respiratory activity required for song production. RAm and PAm receive inputs from both DM and RA, and project to inspiratory and expiratory neurons in the spinal cord. RAm also projects to the syringeal motor neurons in nXIIts, and recurrent projections from the ventrolateral medulla terminate in DM and Uva.

The recursive loop or anterior forebrain pathway (AFP; shown in red) connects HVc to RA via area X, DLM, and lateral MAN; it is recursive because to the collateral projection from LMAN to area X. Lesions to nuclei within the AFP affect song development but not the production of adult song. A parallel but more medial set of nuclei (DMP, the medial extension of area X, and medial MAN) is shown in orange and connects to the song output pathway via HVc.

Area X lies within the avian basal ganglia, and receives a dopaminergic input from the substantia nigra (SNc) and the ventral tegmental area (AVT).

The auditory areas are shown in gray. The hindbrain and midbrain auditory areas are identical to those of mammals: the cochlear nucleus (CN), superior olive (SO, lateral lemniscus (LL) all project to MLd (the avian homolog of the inferior colliculus), which in turn projects to the thalamic auditory relay nucleus (Ov). "Field L", the primary target of Ov, has several subdivisions; from Field L there are projections to other auditory areas such as CMM and NCM. NCM is notable because many of its neurons are tuned to conspecific song, and rapidly habituate to novel songs. Areas with strong auditory responses ("shelf" and "cup") are also found immediately adjacent to the song circuit nuclei HVc and RA; and, in fact, auditory responses can be recorded in most song circuit nuclei (many of these responses are specifically tuned to the bird's own song).

For a full account of the songbird vocal and auditory circuitry, see:

Reiner, Perkel, Mello, and Jarvis (2004) Songbirds and the revised avian brain nomenclature. In Behavioral Neurobiology of Birdsong, Zeigler and Marler, eds. Ann. NY Acad. Sci., 1016, pp. 77-108.