Localization of Phonation Integration Center in Rabbits

Abstract

Problem The midbrain periaqueductal gray (PAG) serves as a phonation integration center, coordinating respiratory, laryngeal, and orofacial activity during vocalization. The objective of this pilot study was to explore electrical excitation of the midbrain PAG for eliciting vocalization using an in-vivo rabbit preparation and determine the feasibility of using image guidance for improved localization of target midbrain structures. Methods Pilot experiments were conducted using four New Zealand White (NZW) breeder rabbits. In the first experiment, a stereotaxic frame was used to guide stimulation of the midbrain PAG without the use of image guidance. Decisions regarding track placements were directed by a stereotaxic atlas of the NZW rabbit brain. Histologic stains of axial brain sections were then obtained to determine electrode track positioning. In a subsequent experiment, magnetic resonance imaging (MRI) and computed tomography (CT) scans were obtained and used to localize midbrain structures for advanced planning capabilities. Results Without the use of image guidance, phonation was feasible, measuring 80–100 Hz using electrical excitation of the midbrain PAG (0.5 to 1.5 mA, 200 Hz, 2 second train duration). However, precise localization of the midbrain PAG proved technically challenging. Using CT and MRI data, scans could be loaded onto an image guided surgical system and combined using an image fusion tool for advanced planning. Conclusion The authors demonstrate the feasibility of electrical excitation of the midbrain PAG to produce vocalization in rabbits using a stereotaxic brain atlas and offer an alternative approach using image guidance for advanced planning and more precise localization of target midbrain structures. Significance The biomechanical forces of phonation and dynamic nature of vocal fold remodeling have created a need for chronic animal preparations to investigate these reparative processes in-vivo. Image guided techniques may improve the feasibility of brain stimulation techniques for eliciting and studying time dependent changes in vocal fold remodeling. Support NIH-NIDCD R03 DC008400.