Effect of uvulonodular lesions on optokinetic nystagmus and optokinetic after-nystagmus in cats.

To investigate the effect of uvulonodular lesions on horizontal optokinetic nystagmus (OKN) and optokinetic after-nystagmus (OKAN), 6 cats were tested before and after lesions made by ablation under anesthesia. In the 3 cats with only uvular lesion, the initial slow phase velocity and the time constant of OKAN were unchanged. In the remaining three cats whose lesions included not only the uvula but also the nodulus, the time constant of OKAN was markedly prolonged, and the initial OKAN velocity was not affected. The postoperative average time constant of OKAN increased from normal value of 9 s to about 40 s. In contrast, OKN was unchanged in all of the 6 animals. These findings indicate that the nodulus may contribute to the discharge characteristics of the velocity storage integrator.