Visual-field-specific heterogeneity within the tecto-rotundal projection of the pigeon

The organization of the tecto-rotundal projection of the pigeon was investi gated by means of anterograde and retrograde tracing techniques. Besides th e known organization in tecto-rotundal connectivity, this study additionall y demonstrates major variations in the ascending projections of different t ectal subfields. We show that the ventral tectum opticum (TO) has significa ntly more projections onto the nucleus rotundus (Rt) than dorsal tectal are as. This difference coincides with differential innervation densities of af ferent fibres within rotundal subregions. While ventral tectal efferents pr oject onto the ventral and central Rt, dorsal tectal efferents mainly arbor ize within limited areas between the central Rt and its dorsal cap, the nuc leus triangularis. Thus, the ventral TO, representing the lower and frontal field of view, exhibits a quantitatively and spatially enhanced projection onto the Rt, as compared with the dorsal TO. The data presented here demon strate a visual field-dependent projection pattern of ascending tectal outp uts onto different rotundal domains. The data are consistent with behaviour al studies, demonstrating tectofugal lesions to suppress visual stimulus an alysis mainly within the frontal field of view.