Regulation of ipsilateral visual information within the tectofugal visual system in zebra finches

The eyes of zebra finches are placed laterally, the foveae are looking into different directions. It is unlikely that the birds are able to process different images from both eyes simultaneously. A neural mechanism might therefore be necessary to guide the birds' attention to one of the two eyes and to reduce the processing of information of the other. Previous studies revealed that information from the ipsilateral eye is indeed suppressed on its way to the telencephalon by the activity of the contralateral eye. It has been suggested that two nuclei of the tecto-thalamic tract, nucleus subpraetectalis and nucleus interstitio praetecto subpraetectalis, are a central part of such a suppressive mechanism. Using electrophysiological recordings, we investigated the influence of these two nuclei and nucleus rotundus on the processing of binocular visual information by treating the nuclei with picrotoxin or electrolytic lesions. Deactivation of inhibitory neurons within SP/IPS leads to a significant increase of the ectostriatal responses to ipsilateral and bilateral stimulation, the responses to contralateral stimulation remain unaffected. Lesioning SP/IPS does not alter the responses to visual stimuli. Treatment of nucleus rotundus with picrotoxin increases contralaterally and bilaterally, but not ipsilaterally evoked responses. A wiring diagram is presented which interprets these findings.