Subcortical projections of the cerebral nystagmogenic area

In the present investigation we analyzed the connections of the cerebral nystagmogenic center with subcortical formations in the guinea pig by electrophysiological methods. Single-shock electrical stimulation of the parietotemporal nystagmogenic area elicited typical evoked potentials in various subcortical structures with latencies ranging from 0.7 msec up to 9 msec. Such evoked potentials could be recorded from ipsilateral internal capsule, most lateral part of the cerebral peduncle, lateral and medial geniculate bodies, lateral and posterior nuclei of the thalamus, superior and inferior brachia, superior and inferior colliculi, oculomotor nuclei, mesencephalic reticular formation, lateral lemniscus and lateral vestibular nuclei. Usually no contralateral responses were seen. Often the evoked potentials were localized in or around the mesodiencephalic nystagmogenic center, which in some experiments was also previously identified. In several cases the experimental arrangement was reversed and it was possible to elicit antidromic evoked potentials in the cerebral nystagmogenic center by stimulating the previously recorded subcortical sites. Thus the results of the present research on the anatomical connections of the cerebral nystagmogenic area with some subcortical formations confirm and extend preceding findings obtained with the Marchi method.