Asymmetry of vertical optokinetic nystagmus and afternystagmus.

The sensorimotor mechanism to stabilize the visual field in upright posture is not the same in earth-horizontal plane and vertical plane, because gravity possesses a directionality which is sensed by gravity-receptors. In this communication, asymmetric behavior of the vertical optokinetic nystagmus and afternystagmus is discussed, in conjunction with lesion placements within the peripheral and central neuro-networks (macula sacculi and cerebellar uvula and nodulus) in squirrel monkeys.