Single cell responses from the optic tectum of the zebra finch (Taeniopygia guttata castanotis Gould)

Responses of neurons of the optic tectum, the prominent, highly laminated m esencephalic station of the tectofugal visual pathway in birds, to computer -generated and other visual stimuli were examined in zebra finches. Our stu dy shows that the contralateral retina projects to the tectum in topographi c order. The representation of the visual field is tilted against the horiz on by 22 degrees. The representation of the contralateral hemifield extends to the ipsilateral side by 15 degrees. Most neurons have receptive fields with excitatory centres of different shapes and inhibitory surround. A hew type of neuronal receptive field is described which has an excitatory centr e and a surround which is movement sensitive and preferably excited by very small spots. The first type of neurons is mostly located in upper tectal l ayers, the latter only in deeper layers. Excitatory centre sizes increase w ith depth, and there is a tendency of smaller receptive fields in the fovea l region. The representation, of the frontal visual field does not show spe cializations which could be expected if it were used for fixation of grain during pecking. Our results are in accordance with previous behavioural exp eriments.