Effects of early monocular deprivation on visual input to cat nucleus of the optic tract

Single cells were recorded extracellularly in the nucleus of the optic tract (NOT) in monocularly deprived cats. Monocular deprivation had no effect on the direction specificity of these neurons, i.e. all cells in the left nucleus preferred movements from right to left and all units in the right nucleus preferred movements from left to right in the visual field. Neurons driven from the deprived eye failed to respond to stimuli moving at velocities above 10 degrees/s whereas neurons driven from the non-deprived eye responded to velocities up to and above 100 degrees/s as do neurons in normal cats. In 8 out of the 10 cats tested all cells in the two nuclei could be influenced only from the contralateral eye irrespective whether this was the deprived or the non-deprived eye. In the other two cats the influence from the non-deprived eye on cells in the ipsilateral NOT was found to be normal. This influence is mediated probably via cortico-fugal projections. In the 8 abnormal cats a clear deprivation effect could be assigned for the first time to the non-deprived eye consisting in a loss of its connections to the ipsilateral NOT. Electrical stimulation of the visual cortex revealed, however, the existence of a connection between the visual cortex and the NOT. A possible explanation for the specific deficit with visual stimulation in the cortico-pretectal synapse ipsilateral to the non-deprived eye is discussed in relation to developmental mechanisms. The conduction velocity of retinal input to the NOT and the output of the NOT to the inferior olive remained uninfluenced by visual deprivation.