Sources for connectivity of neural populations adjacent to songbird vocal nuclei

The first column shows the connection; arrows indicate axonal projections. The second column indicates the tracer direction studied; connections determined in both the anterograde and retrograde directions are accepted with more confidence than ones determined only in one direction. The third column lists the references where these connections were determined. The AN = >LAI & ASt indicates that AN neurons send collateral projections to LAI and ASt adjacent to RA and Area X respectively, which is similar to the collateral projections from individual LMAN neurons to RA and Area X. In the studies before 2004, the old avian brain nomenclature was used and terminology varied between studies. AN was called the LMAN shell or frontal neostriatum, DLN we consider here as a part of NCL (see main text), LAI was called dorsal archistriatum (Ad), and ASt and Area X was within a region called the lobus parolfactorius. PMN is premotor neurons of the brainstem, medulla, and possibly spinal cord. Here, we adopted a terminology that is applicable across all avian species, vocal learners and non-learners.