A Golgi-Based Cytoarchitectonic Analysis of The Premotor Cortex in the Zebra Finch

Abstract

The zebra finch song system is a powerful model for studying the neural basis of learned vocal behavior, yet the regional cytoarchitectonic organization of its premotor nuclei remains incompletely defined. In this study, we used the Golgi stain to examine the structural organization of the song system in adult male and female zebra finches, with particular emphasis on the high vocal center (HVC) and the robust nucleus of the arcopallium (RA). Brains were sectioned parasagittally at 150 µm, imaged using laser scanning confocal microscopy, and analyzed. We generated atlas-like histological images of major forebrain regions, quantified maximal cross-sectional area and estimated volume of HVC and RA, characterized soma-profile distributions within HVC, and performed orientation analysis as a regional measure of local structural anisotropy. Our findings revealed marked sexual dimorphism in the zebra finch premotor song system. Male birds exhibited larger HVC and RA cross-sectional areas and estimated volumes than female zebra finches. Within HVC, soma-size-defined populations were distributed nonuniformly across sampled regions: large-soma candidates were enriched medially, whereas smaller subclass-like populations were more prominent laterally. Orientation analysis further indicated sex-dependent differences in regional structural organization, with males showing a stronger directional bias in the HVC-RA spanning region and females showing a comparatively more diffuse pattern. Together, these findings show that sexual dimorphism in the zebra finch song system extends beyond overall nucleus size to include internal spatial organization. This work provides a region-level cytoarchitectonic framework for HVC and RA and establishes a foundation for future studies combining Golgi staining with cell-type-specific and higher-resolution approaches to link structure more directly to vocal motor function.