Three-dimensional analysis of avian song control nuclei

Analysis of seasonal and developmental changes in the morphology of avian song control nuclei has traditionally been performed using two-dimensional (2-D) cross-sectional traces from brain sections. This method, although reliable, does not encompass the possibility that subdivisions of a nucleus might change in size to different degrees. Three-dimensional (3-D) analysis of song nuclei under different conditions could provide insight on this issue. This approach could also be of value in guiding and evaluating the use of lesions to study the functions of subdivisions of song nuclei. We used customized computer software to produce 3-D images of song nuclei from 2-D brain sections of spotted towhees (Pipilo maculatus) in different hormonal status, and from Gambel's white-crowned sparrows (Zonotrichia leucophrys gambelii) with unilateral lesions of the higher vocal center (HVc). 3-D images show that some sub-regions of song nuclei indeed change in size to a greater extent than others. 3-D analysis of HVc lesions provides a clearer view of the size and shape of the lesion site within the target nucleus and relative to the surrounding tissue. Used in conjunction with 2-D analysis, the 3-D method will aid investigations of the song system and contribute to the understanding of its regulation by hormones.