An underestimated visual pathway in reptiles.

Field potentials evoked in the turtle general cortex by electric stimulation of the optic tectum were analyzed. Cathodal polarization and subtotal lesions of n. rotundus led to either facilitation or depression of later components of the cortical potential. On the contrary, cathodal polarization and lesions of n.geniculatus lateralis dorsalis similarly affected the initial component. After 21-23 months following eye enucleation or optic nerve section, the conduction of fast tectal volleys to the general cortex via n. geniculatus lateralis dorsalis was blocked, though the conduction of tectal impulses to the dorsal ventricular ridge via n.rotundus survived. It is concluded that in turtles one more visual channel, i.e., retino-tecto-geniculo-cortical, is functioning, in addition to well-known retino-tecto-rotundo-telencephalic and retino-geniculo-cortical channels.