The Effect of Head Reorientation on the Direction of Postrotatory Nystagmus in Humans

While it has been shown that reorienting the head with respect to gravity during postrotatory nystagmus (PRN) affects the decay of PRN, little is known about the influence on the axis of eye rotation during PRN. We therefore investigated 10 normal human subjects by means of search coil recordings using a variety of head reorientation paradigms in a randomized order during PRN after stop from a 90 degrees/s rotation about earth vertical. For most conditions, a reorientation of the head with respect to gravity 2 s after the rotation had stopped did not alter significantly the eye velocity vector of PRN with respect to head coordinates. This strongly indicates that PRN in humans is mainly stabilized relative to the head and not relative to space.