title: Eye position dependency of nystagmus during constant vestibular stimulation.
abstract: Alexander's law, the eye position dependency of nystagmus due to peripheral vestibular lesions, has been hypothesized to occur due to adaptive changes in the brainstem velocity-to-position neural integrator in response to non-reciprocal vestibular stimulation. We investigated whether it develops during passive head rotations that produce constant nystagmus for >35 s. The yaw rotation stimulus consisted of a 1-s acceleration (100°/s(2)), followed by a lower acceleration ramp (starting at 7.3°/s(2) and increasing at 0.04°/s(2)/s) until 400°/s was reached after 38 s. This stimulus was designed to offset the ~15 s vestibular ocular reflex time constant (and the 150 s adaptation time constant) and produce constant velocity slow phases. In contrast to peripheral lesions, this vestibular stimulation is the result of real head turns and has the push-pull characteristics of natural movements. The procedure was successful, as the average velocity of 31°/s was unchanged over the final 35 s of the acceleration period. In all 10 healthy human subjects, we found a large and stable Alexander's law, with an average velocity-versus-position slope of -0.366 in the first half that was not significantly different in the second half, -0.347. These slopes correspond to integrator time constants of <3 s, are much less than normal time constants (~25 s), and are similar to those observed in patients with peripheral vestibular lesions. Alexander's law also developed, on average, in 10 s. We conclude that Alexander's law is not simply a consequence of non-reciprocal vestibular stimulation.
authors: Department of Neurology, University Hospital Zürich, Frauenklinikstrasse 26, 8091 Zurich, Switzerland. chris.bockisch@usz.ch
authors: Christopher J
authors: CJ
authors: Bockisch
authors: Elham
authors: E
authors: Khojasteh
authors: Dominik
authors: D
authors: Straumann
authors: Stefan C A
authors: SC
authors: Hegemann
mesh_terms: D000054:Acceleration; D053483:Eye Movement Measurements; D006801:Humans; D009760:Nystagmus, Physiologic / Q000502:physiology*; D010775:Photic Stimulation / Q000379:methods*; D012027:Reflex, Vestibulo-Ocular / Q000502:physiology*
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