Asymmetric optokinetic after-nystagmus induced by active or passive sustained head rotations.

Asymmetric vestibular function affects optokinetic after-nystagmus (OKAN) in man, but little is known about the involvement of cervical proprioception in the visual-vestibular interaction reflected as OKAN. We studied the effect of asymmetric cervical proprioception induced by active maximal, or passive 70 degrees sustained horizontal head rotations on OKAN in 16 healthy subjects. We evoked optokinetic nystagmus (OKN) by means of a whole-field optokinetic drum rotated at a velocity of 90 degrees/s for 60 s. Following left- and right-beating OKN, we recorded OKAN in complete darkness for 60 s by DC electro-oculography. Both passively and actively sustained head rotations significantly reduced the intensity of OKAN beating in the direction opposite to the head rotation, while OKAN beating in the direction of the head rotation remained unchanged. This resulted in significant asymmetry between OKAN beating in the direction of the head rotation vs. that in the opposite direction. The findings show that in normal subjects neck proprioception converges with visual and vestibular signals and affects subcortical OKN. Asymmetric neck proprioception from neck disorders may be hypothesized to induce dizziness or vertigo in situations where OKN is evoked.