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 stimulation for epilepsy. Methods: Bilateral deep-brain stimulating electrodes were inserted in the centromedian nucleus of the thalamus to control seizures in a patient with intractable epilepsy. Results: Cathodal high-frequency stimulation through the deepest contact of each electrode elicited cycles of slow ipsi-versive conjugate eye deviations, each followed by rapid contralateral jerks. The involved electrode contacts were situated at the mesodiencephalic junction just inferior to the centromedian nucleus of the thalamus and rostral to the superior colliculus. Right-sided stimulation evoked left beating nystagmus and left-sided stimulation evoked right beating nystagmus. Stimulation through other electrode contacts did not induce nystagmus. Electronystagmography showed the nystagmus 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 nonhuman primates to play a role in the generation of optokinetic nystagmus.