We showed that, in the Anterior Forebrain Pathway (AFP) of the song system, the
basal ganglia nucleus Area X receives input from the thalamic nucleus, DLM, as
well as adjacent subregions of cerebellar-recipient dorsal thalamus
(DTCbN) (blue arrows). Hence DLM provides feedback to Area X
similar to projections from thalamus to the striatum in mammals, and
DTCbN provides a route for output from the cerebellar nuclei
(CbN, red arrow) to reach the basal ganglia in the song system through thalamus.
More posterior and medial regions of DTCbN project to medial striatum
outside of Area X (lighter blue arrow). We also found that DTCbN
projects to nidopallium outside of cortical song system nucleus LMAN (lighter
blue arrow), implying that DTCbN may communicate both with the song
system and with general motor areas outside the song system. Canonical nuclei of
the song system are outlined in heavy black lines.