Tectocortical connections in the rat visual system.

Electrical stimulation of the superior colliculus by square pulses evokes responses in the ipsilateral occipital region whose localization coincides with the zone of evoked potentials to photic stimulation. The short latent period of the visual cortical evoked potentials to stimulation of the superior colliculus (mean 3.2 +/- 1.1 msec; P less than 0.05) together with morphological data suggests that only one relay, in the structures of the thalamus, occurs along the tectocortical pathway in the rat visual system. In the poorly differentiated cortex of the rat no separate representation of retino-geniculo-cortical and tectocortical channels could be found.