Convergence rotatory nystagmus under unusual conditions of semicircular canal and otolith stimulation

The characteristics of interaction between two vestibular subsystems (otiliths and semicircular canals) were studied by means of binocular (bilateral) videooculographic recording of eye movements in 43 men aged from 19 to 41 years that had been found healthy upon aviation physical examination. The time course of horizontal vestibular nystagmus was analyzed separately for each eye in subjects who bent forward and straightened up in the sagittal plane while being rotated about the vertical body axis in an electrically driven rotating chair. This combined rotation caused interocular asymmetric nystagmus in 91% of the subjects and convergence rotatory nystagmus in 42% of the subjects. A hypothesis on the mechanism of interocular asymmetric nystagmus caused by the combined rotation and convergence rotatory nystagmus as its special case has been advanced. The hypothesis allows for independent nystagmic mechanisms (subsystems) for the right and left eyes.