Previous electrophysiological studies in pigeons have shown that the complex spike activity of Purkinje cells in the medial vestibulocerebellum (nodulus and ventral uvula) is modulated by patterns of optic flow that result from self-translation along a particular axis in three-dimensional space. There are four response types based on the axis of preferred translational optic flow. By using a three axis system, where +X, +Y, and +Z represent rightward, upward, and forward self-motion, respectively, the four cell types are t(+Y), t(-Y), t(-X-Z), and t(-X+Z), with the assumption of recording from the left side of the head. These response types are organized into parasagittal zones. In this study, we injected the anterograde tracer biotinylated dextran amine into physiologically identified zones. The t(-X-Z) zone projected dorsally within the vestibulocerebellar process (pcv) on the border with the medial cerebellar nucleus (CbM), and labeling was found in the CbM itself. The t(-X+Z) zone also projected to the pcv and CbM, but to areas ventral to the projection sites of the t(-X-Z) zone. The t(-Y) zone also projected to the pcv, but more ventrally on the border with the superior vestibular nucleus (VeS). Some labeling was also found in the dorsal VeS and the dorsolateral margin of the caudal descending vestibular nucleus, and a small amount of labeling was found laterally in the caudal margin of the medial vestibular nucleus. The data set was insufficient to draw conclusions about the projection of the t(+Y) zone. These results are contrasted with the projections of the flocculus, compared with the primary vestibular projection, and implications for collimotor function are discussed.

Abstract-The ventral tegmental area (catecholaminergic group A10) is a midbrain region characterized by concentrated dopaminergic immunoreactivity. Previous studies in pigeons show that the ventral tegmental area provides a robust projection to the hippocampal formation and to the medial column of the inferior olive. However, the distribution, morphology, and neurochemical content of the neurons that constitute these projections have not been resolved. In this study, we used a combination of retrograde tracing techniques and immunofluorohistochemistry to address these issues. Retrograde tracers were used to demonstrate that the distribution of ventral tegmental area neurons projecting to the hippocampus and the inferior olive overlap in the caudoventral ventral tegmental area. The hippocampus-and inferior olive-projecting ventral tegmental area neurons could not be distinguished based on morphology: most neurons had small-to medium-sized multipolar or fusiform soma. Doublelabeling with fluorescent retrograde tracers revealed that the hippocampus-and medial column of the inferior olive-projecting neurons were found intermingled in the ventral tegmental area, but no cells were double labeled; i.e. individual ventral tegmental area neurons do not project to both the hippocampal formation and medial column of the inferior olive. Finally, we found that a minority (8.2%) of ventral tegmental area neurons providing input to the hippocampus were tyrosine hydroxylase-immunoreactive, whereas none of the inferior olive-projecting neurons were tyrosine hydroxylase positive. Combined, our findings show that the projections to the hippocampus and olivocerebellar pathway arise from intermixed subpopulations of ventral tegmental area neurons with indistinguishable morphology but only the hippocampal projection involves dopaminergic neurons. We suggest that equivalent projections from the ventral tegmental area to the hippocampal formation and inferior olive exist Ventral tegmental area (VTA; catecholaminergic group A10) is a midbrain region characterized by dense dopaminergic immunoreactivity (Lindvall and Björklund, 1983; for review see Oades and Halliday, 1987;Gasbarri et al., 1997). In birds, the VTA, (formerly known as the area ventralis of Tsai (Reiner et al., 2004)), resides medial to the nucleus of the basal optic root (nBOR) and lateral to the third cranial nerve (Fuxe and Ljunggren, 1965;Ikeda and Gotoh, 1971;Dube and Parent, 1981;Kiss and Péczely, 1987;Bailhache and Balthazart, 1993;Moons et al., 1994;Wynne and Güntürkün, 1995;Durstewitz et al., 1999). The VTA gives rise to a robust dopaminergic input throughout the telencephalon that has been implicated in various behaviors including cognition, reward, motivation, and motor function (for review, see Horel, 1988;Oades and Halliday, 1987;Gasbarri et al., 1997;Wise 2004).In the present study, we characterized two efferent pathways of the VTA (illustrated in Fig. 1) that have been implicated in behaviors requiring the analysis of the distinct visual patterns produced dur...