Visual suppression of caloric nystagmus and optokinetic responses in cats

Previously it was reported that loss of visual suppression (VS) was accompanied by disturbance of optokinetic nystagmus (OKN) in monkeys with lesions at the flocculus. In the present experiment with cats, OKN was investigated after inflicting lesions on either superior colliculus (SC) or inferior olive (IO), both of which are considered to be the main prefloccular relay nuclei to mediate visual signals to the flocculus. VS of caloric nystagmus was recognized in all the IO-lesioned cats and OKN remained normal except in one cat. After the left SC lesions, loss of VS was evidently revealed and optokinetic stimuli produced directional preponderance to the left with diminished responses to the right in 7 of 9 cats. The present findings suggest that the SC may be an important relay nucleus to the flocculus in conveying visual signals responsible for VOR gain.