arcopallium

Arcopallium is a major region of the avian forebrain, comprising a collection of nuclei in the ventral telencephalon that forms part of the basal ganglia–like circuitry in birds. It encompasses several subnuclei, including the robust nucleus of the arcopallium (RA) in songbirds, which is a well-studied component of the song-control system.

Anatomy and subdivisions: The arcopallium is subdivided into medial and lateral portions, with the RA lying in the lateral arcopallium. The nucleus taeniae of the amygdala is frequently discussed in relation to arcopallium, though its exact boundaries vary among species.

Connectivity and function: Arcopallial circuits receive inputs from pallial areas involved in sensorimotor processing and, in oscine birds, from the song system nuclei HVC and LMAN. The arcopallium sends major outputs to brainstem motor nuclei controlling vocalization and movement, including projections from RA to the nucleus retroambigualis and to the tracheosyringeal part of cranial nerve XII (the hypoglossal nucleus) that direct the syrinx. This arrangement underpins learned motor sequencing and vocal production in birds and contributes to motor learning more broadly.

Relevance: In comparative neuroscience, the arcopallium serves as a key model for studying basal ganglia–like circuitry in non-mammalian vertebrates and for exploring how complex vocal behaviors are learned and controlled. Lesions or inactivation of arcopallial regions can disrupt song structure and motor timing, highlighting its role in coordinated motor output.