Central nystagmus induced by deep-brain stimulation for epilepsy

Purpose: The goal of the present study was to describe the localization of central nystagmus induced as a side effect of electrical deep-brain stimula tion for epilepsy. Methods: Bilateral deep-brain stimulating electrodes were inserted in the c entromedian nucleus of the thalamus to control seizures in a patient with i ntractable epilepsy. Results: Cathodal high-frequency stimulation through the deepest contact of each electrode elicited cycles of slow ipsi-versive conjugate eye deviatio ns, each followed by rapid contralateral jerks. The involved electrode cont acts were situated at the mesodiencephalic junction just inferior to the ce ntromedian nucleus of the thalamus and rostral to the superior colliculus. Right-sided stimulation evoked left beating nystagmus and left-sided stimul ation evoked right beating nystagmus. Stimulation through other electrode c ontacts did not induce nystagmus. Electronystagmography showed the nystagmu s to have constant velocity slow phases. Conclusions: A central nystagmogenic area exists in humans that appears to be homologous to the nucleus of the optic tract, a region described in nonh uman primates to play a role in the generation of optokinetic nystagmus.