Effect of otolith end organ ablation on pendular rotation nystagmus in squirrel monkeys

Damped pendular rotation nystagmus was studied in squirrel monkeys before and after otolith end organ ablation (two-stage operations). After each operation, the nystagmic slow phase eye speed toward the operated side was reduced (to about 73% of that before the operation) and that to the non-operated side did not show any marked change. A few subjects showed spontaneous nystagmus with amphetamine administration but only in dark (could not be found in light) immediately after the operation, and it disappeared rapidly. Therefore, this post-ablative reduction of the slow phase eye speed is considered to result from the loss of inputs from the otolith end organs.