Loss of visual suppression of caloric nystagmus in cats.

Loss of visual suppression (VS) of caloric nystagmus was produced after creating flocculus lesions. The flocculus receives visual signals through a climbing fiber pathway via the inferior olive (IO) and through a mossy fiber pathway (MF) presumably via the superior colliculus (SC). In order to elucidate the prefloccular nuclei responsible for VS of caloric nystagmus, VS of caloric nystagmus was investigated after making lesions in such nuclei as the SC and the IO in 42 cats. After the IO lesion, VS of caloric nystagmus was revealed in all IO-lesioned cats throughout the whole experimental course. After the SC lesion, loss of VS was constantly observed and persisted in 7 out of 9 cats. Hence, the MF pathway via the SC is believed to be the most likely candidate for the immediate modification of the vestibuloocular reflex by visual stimuli.