Nystagmus evoked in the rabbit by electrical stimulation of the lateral geniculate body

Effects of blindfolding a unilateral eye on so-called central nystagmus

A bipolar stimulating electrode was chronically implanted at the mesodiencephalon in the rabbit to induce so-called central nystagmus. The nystagmus was remarkably facilitated in either darkness by blindfolding an eye ipsilateral to the stimulation site, but the nystagmus was almost never facilitated by blindfolding an eye contralateral to the stimulation site. This is a phenomenon related to photic inhibition. This phenomenon disappeared after ablation of the flocculus and paraflocculus ipsilateral to the stimulation site. The neural pathway responsible for it is considered to be by way of the flocculus.

Oculomotor areas in the rabbits midbrain and pretectum

The role of some meso- and diencephalic structures in eye movements was investigated by ablation and stimulation experiments. Optokinetic nystagmus was abolished by small lesions in the lateral pretectum, but not by complete removal of the superior colliculi. Stimulation of the superior colliculus and other visual centers was effective in eliciting nystagmus (slow phase ipsilateral), but the most efficient trigger zones are found in the lateral pretectum and the midbrain tegmentum. Only from these areas could nystagmus still be elicited after degeneration of the primary optic fibers. The lateral pretectal trigger zone is probably identical with the nucleus of the optic tract. It is postulated that this nucleus is an essential station for horizontal optokinetic reactions. Saccades were obtained by stimulation of the mesencephalic central grey, but not for any visual centers such as the superior colliculus.