Exploring Anatomical Links Between the Crow’s Nidopallium Caudolaterale and its Song System

Abstract Crows are corvid songbirds that exhibit remarkable cognitive control over their actions, including their vocalizations. They can learn to vocalize on command and the activity of single neurons from the crow’s associative telencephalic structure nidopallium caudolaterale (NCL) is correlated with the execution of this vocal and many non-vocal skilled behaviors. However, it remains unknown if specific anatomical adaptations that directly link the crow NCL to any of the nuclei of the crow’s “song system” exist. To address this issue, we used fluorescent tracers along with histological staining methods (Nissl-, myelin-, and anti tyrosine hydroxylase) to characterize the connectivity of the crow’s NCL in relation to its song system nuclei. We found that the NCL sends dense projections into the dorsal intermediate arcopallium (AID) directly adjacent to and engulfing the robust nucleus of the arcopallium (RA), which is the telencephalic motor output of the song system. Similarly, we demonstrate dense NCL projections into the striatum surrounding the basal ganglia song nucleus “area X”. Both of these descending projections mirror the projections of the nidopallial song nucleus HVC (proper name) into RA and area X, with extremely sparse NCL fibers extending into area X. Furthermore, we characterized the distribution of cells projecting from the lateral part of the magnocellular nucleus of the anterior nidopallium (MAN) to NCL. Notably, a separate medial population of MAN cells projects to HVC. These two sets of connections—MAN to NCL and MAN to HVC—run in parallel but do not overlap. Taken together, our findings support the hypothesis that the NCL is part of a “general motor system” that parallels the song system but exhibits only minimal monosynaptic interconnections with it.