Topographic organization of inferior olive cells projecting to translational zones in the vestibulocerebellum of pigeons

In the nodulus and ventral uvula of pigeons, there are four parasagittal zones containing Purkinje cells responsive to patterns of optic flow that results from self-translation along a particular axis in three-dimensional space. By using a three-axis system to describe the preferred direction of translational optic flow, where +X, +Y, and +Z represent rightward, upward, and forward self-motion, respectively, the four cell types are: +Y, -Y, -X-Z, and -X+Z (assuming recording from the left side of the head). The -X-Z zone is the most medial, followed in sequence by the -X+Z, -Y zone, and the +Y zones. In this study, we injected the retrograde tracer cholera toxin subunit B into each of the four translational zones to determine the origin of the climbing fiber inputs in the inferior olive. Retrograde labeling in the inferior olive was found in the ventrolateral margin of the medial column from injections into all four translational zones; however, there was a clear functional topography. Retrograde labeling from -Y zone injections was found most rostrally in the medial column, whereas retrogradely labeled cells from -X-Z zone injections were found most caudally in the medial column. Labeling from +Y and -X+Z zone injections were found between the labeling from -Y zones and -X-Z zones, with +Y labeling located slightly caudal to -X+Z labeling.