Quantitative analysis of horizontal and vertical optokinetic nystagmus and optokinetic after-nystagmus in the cat

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This study reported on the horizontal optokinetic nystagmus (OKN) and vertical OKN of cats under the same conditions with quantitative parameters. Using the search coil method, the horizontal and vertical OKN was investigated in 5 alert cats in an upright position. As the optokinetic stimulus, a stepped random dot pattern was used. We recorded the quantitative parameters in both the horizontal and vertical OKN (for the direct pathway parameters, initial fast rise and fast fall; for the indirect pathway parameters, steady state slow phase velocity [SPV] and the optokinetic after-nystagmus [OKAN] area) in cats. The SPV of the horizontal OKN increased with the stimulus amplitude up to 40-60 degrees/s but saturated thereafter (in some cats even more). Right and left OKN were almost symmetrical. The SPV of the downward OKN increased with the stimulus amplitude up to 20 degrees/s but saturated thereafter. This was lower than the horizontal OKN. On the other hand, the SPV of the upward OKN was weak and irregular. As for the OKAN, the right and left OKAN was also almost symmetrical. A downward OKAN was also observed but was weaker than the horizontal OKAN. A fast fall in the SPV of the OKAN was observed in the horizontal and downward OKN. On the other hand, there was little upward OKAN. OKN in cats was composed of both a direct pathway and an indirect pathway. This study suggested that directional differences of OKN were mainly responsible for the indirect pathway. Both the direct and indirect pathways of cats were smaller than those of monkeys. This suggested that the differences in OKN between cats and monkeys were mainly responsible for the direct pathway.