Integration of information from both eyes by single neurons of nucleus rotundus, ectostriatum and lateral neostriatum in the zebra finch (Taeniopygia guttata castanotis Gould).

Although the optic nerve in birds crosses completely, visual information from the ipsilateral eye also reaches the ectostriatum, the telencephalic statibon of the tectofugal pathway, by recrossing fibers. These recrossing projections connect the contralateral tectum opticum with the ipsilateral nucleus rotundus, which in turn projects to the ectostriatum. The ectostriatum itself projects to the overlying lateral neostriatum, an area which serves an important role in sexual imprinting. This study shows that contralateral and ipsilateral information converges on single neurons within the nucleus rotundus, the ectostriatal region and the lateral neostriatum. In the three brain areas almost all isolated neurons exhibited responses to contralateral as well as bilateral visual stimuli. The number of neurons responding to ipsilateral stimuli increases from nucleus rotundus to the lateral neostriatum. We did not find any neurons driven exclusively by ipsilateral stimuli. The strength of ipsilateral responses is rather weak within the nucleus rotundus and ectostriatum, but shows a sharp increase in the lateral neostriatum. For most neurons of nucleus rotundus and ectostriatum, an additional ipsilateral stimulus did not significantly affect the response to a contralateral one. In contrast, a strong excitatory effect can be found in the neostriatum. The results are in agreement with previous evoked-potential studies and give new insights on the integration of ipsilateral and contralateral stimuli in zebra finch tectofugal visual pathway.