Bottom-up activation of the vocal motor forebrain by the respiratory brainstem

Brainstem motor structures send output commands to the periphery and are dynamically modulated by telencephalic inputs. Little is known, however, about ascending brainstem control of forebrain motor structures. Here, we provide the first evidence for bottom-up activation of forebrain motor centers by the respiratory brainstem. We show that, in the avian vocal control system, activation of the brainstem inspiratory nucleus paraambigualus (PAm), a likely homolog of the mammalian rostral ventral respiratory group, can drive neural activity bilaterally in the forebrain vocal control nuclei HVC (used as a proper name) and the robust nucleus of the arcopallium (RA). Furthermore, this activation is abolished by lesions of nucleus uvaeformis (Uva), a thalamic nucleus necessary for song production. We identify a type of bursting neuron within PAm whose activity is correlated, in an Uva dependent manner, to bursting activity in RA, rather than to the respiratory rhythm, and is robustly active during the production of stimulus evoked vocalizations. Because this ascending input results in cross-hemisphere activation, our results suggest a crucial role for the respiratory brainstem in coordinating forebrain motor centers during vocal production.