Cellular Mechanisms of Vocal-Respiratory Integration

Duke University, Durham NC

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Abstract

These experiments address how respiratory and telencephalic afferents shape the activity of vocal motorneurons used for learned vocalizations. In those few vertebrate species where vocal learning occurs, such as humans and songbirds, the telencephalon plays a critical role in modulating respiratory- vocal interactions within the brainstem. In songbirds, a prominent role for the telencephalon in respiratory-vocal integration is suggested by a major projection from the nucleus robustus archistriatalis (RA), the sole output of the telencephalic vocal control network, to vocal (i.e., syringeal) motorneurons in the tracheosyringeal portion of the nucleus hypoglossus (NXIIts) and to medullary regions that house respiratory premotor neurons as well as neurons that project upon NXIIts. Songbirds constitute the system of choice in which to study how telencephalic activity influences respiratory-vocal integration, especially with respect to vocal learning, because: 1) avian song learning occurs during early development in a manner resembling human speech development, 2) the avian and mammalian brainstems are highly homologous and 3) unlike mammals, the vocal neuron pool is spatially separate from, rather than being embedded in, respiratory regions of the medulla. We propose to examine telencephalic-respiratory-vocal interactions at the cellular and synaptic levels. These intracellular electrophysiological and anatomical studies are essential because although much is now known about telencephalic and vocal muscular activity as it relates to birdsong, there remains a deficiency in our knowledge of the synaptic and intrinsic electrophysiology of syringeal motorneurons, especially with respect to their respiratory and telencephalic afferents. The collaborative effort proposed here will unite classical anatomical approaches with in vitro and in vivo intracellular electrophysiological techniques to 1) characterize the electrophysiological and morphological properties of vocal motor and respiratory neurons in the songbird, 2) directly search for the means by which respiratory-related neurons and vocal motor neurons synaptically interact and 3) examine the function of telencephalic inputs to syringeal motorneurons, and how these descending inputs both modulate and are gated by respiratory activity.