The retinal origin of uncrossed optic nerve fibres in rats and their role in visual discrimination.

An attempt was made to sever the optic chiasma in the mid-sagittal plane in 12 rats. This was successful in 8 animals. Provided there was no additional substantial damage to the uncrossed optic fibres the rats were able to relearn an intensity discrimination and to learn or relearn an orientation discrimination, although optokinetic following was abolished. The results unequivocally demonstrate that the uncrossed optic fibres can mediate two kinds of visual discrimination. The area of retina giving rise to the uncrossed fibres was determined from the position of undegenerated retinal ganglion cells in each eye following section of the chiasma, and in one eye of 4 rats in which one optic tract was entirely or extensively destroyed. The ganglion cells giving rise to the uncrossed optic fibres occupy about 40 degrees of the temporal retina, corresponding to the binocular overlap in the visual field.