Zonal organization of the vestibulocerebellum in pigeons (Columba livia): I. Climbing fiber input to the flocculus.

Previous studies in pigeons have shown that the neurons in the medial column of the inferior olive respond best to patterns of optic flow resulting from self-rotation. With respect to the axis of rotation, there are two functional groups: rVA neurons prefer rotation about the vertical axis, whereas rH45 neurons respond best to rotation about an horizontal axis oriented at 45 degrees ipsilateral azimuth. The rVA and rH45 neurons are located in the caudal and rostral margins of the medial column, respectively. These olivary neurons project as climbing fibers to the contralateral flocculus. In this study, injections of anterograde tracers into the medial column were used to investigate the zonal organization of the climbing fiber input to the flocculus of pigeons. Iontophoretic injections of either cholera toxin subunit-B or biotinylated dextrin amine were made into the medial column of the inferior olive at locations responsive to rVA or rH45 rotational optic flow. Anterogradely labeled climbing fibers in the flocculus showed a clear zonal organization. There were four parasagittal bands spanning both folia IXcd and X consisting of two rVA zones interdigitated with two rH45 zones. These findings are compared with the zonal organization of the flocculus in mammalian species.