Presentation (Project) Title

Convergence of Auditory Nerve Fibers onto Globular Bushy Cells

Mentor Information

George Spirou (College of Engineering and Morsani School of Medicine)

Presentation Format

Event

Abstract

Globular bushy cells (GBCs) are well-studied neurons in the ventral cochlear nucleus and are remarkable for encoding temporal features of sound with more precision than auditory nerve fibers (ANFs). Multiple ANFs are known to synapse onto a single GBC, but the average number, size, and physiological effects of these inputs have not been systematically investigated in a fully developed brain. This information is necessary for a comprehensive understanding of the neural encoding of binaural hearing since GBCs are part of binaural convergence pathways in the lower auditory system. Here, Serial-Block-Face-Scanning-Electron-Microscopy was employed to obtain high-resolution images of auditory inputs synapsing onto GBCs. Essentially, 21 GBCs and all their large inputs were carefully reconstructed with cutting-edge meshing algorithms. We found that a range of 5 – 12 large auditory nerve inputs converge onto each GBC, which is higher than previous estimates. GBCs are thought to follow a coincidence detection model of innervation where multiple subthreshold inputs drive cellular activity. Interestingly, this innervation pattern was observed for some of the reconstructed GBCs, while other cells had a distinctly large, dominant input. Thus, we conclude that there are two models of GBC innervation – i.e., a mixed model (1 or 2 suprathreshold inputs and multiple subthreshold) and a coincidence detection model (all subthreshold inputs). The input sizes, somatic/dendritic surface areas, and dendritic branching patterns were incorporated into a GBC computational model, which confirmed the presence of the two innervation models. Furthermore, we present novel discoveries about GBC dendritic structure and explore their functional significance through computational modeling.

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Convergence of Auditory Nerve Fibers onto Globular Bushy Cells

Globular bushy cells (GBCs) are well-studied neurons in the ventral cochlear nucleus and are remarkable for encoding temporal features of sound with more precision than auditory nerve fibers (ANFs). Multiple ANFs are known to synapse onto a single GBC, but the average number, size, and physiological effects of these inputs have not been systematically investigated in a fully developed brain. This information is necessary for a comprehensive understanding of the neural encoding of binaural hearing since GBCs are part of binaural convergence pathways in the lower auditory system. Here, Serial-Block-Face-Scanning-Electron-Microscopy was employed to obtain high-resolution images of auditory inputs synapsing onto GBCs. Essentially, 21 GBCs and all their large inputs were carefully reconstructed with cutting-edge meshing algorithms. We found that a range of 5 – 12 large auditory nerve inputs converge onto each GBC, which is higher than previous estimates. GBCs are thought to follow a coincidence detection model of innervation where multiple subthreshold inputs drive cellular activity. Interestingly, this innervation pattern was observed for some of the reconstructed GBCs, while other cells had a distinctly large, dominant input. Thus, we conclude that there are two models of GBC innervation – i.e., a mixed model (1 or 2 suprathreshold inputs and multiple subthreshold) and a coincidence detection model (all subthreshold inputs). The input sizes, somatic/dendritic surface areas, and dendritic branching patterns were incorporated into a GBC computational model, which confirmed the presence of the two innervation models. Furthermore, we present novel discoveries about GBC dendritic structure and explore their functional significance through computational modeling.