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Eye position dependency of nystagmus during constant vestibular stimulation

Bockisch, Christopher ; Khojasteh, Elham ; Straumann, Dominik ; Hegemann, Stefan

In: Experimental Brain Research, 2013, vol. 226, no. 2, p. 175-182

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    Title
    • Eye position dependency of nystagmus during constant vestibular stimulation
    Author
    • Bockisch, Christopher. Department of Neurology, University Hospital Zürich, Frauenklinikstrasse 26, 8091, Zurich, Switzerland
    • Khojasteh, Elham. Department of Otorhinolaryngology, Head and Neck Surgery, University Hospital Zürich, Zurich, Switzerland
    • Straumann, Dominik. Department of Neurology, University Hospital Zürich, Frauenklinikstrasse 26, 8091, Zurich, Switzerland
    • Hegemann, Stefan. Department of Otorhinolaryngology, Head and Neck Surgery, University Hospital Zürich, Zurich, Switzerland
    Document Type
    • Postprint
    OAI-PMH Identifier
    • oai:doc.rero.ch:313176
    Summary
    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>35s. The yaw rotation stimulus consisted of a 1-s acceleration (100°/s2), followed by a lower acceleration ramp (starting at 7.3°/s2 and increasing at 0.04°/s2/s) until 400°/s was reached after 38s. 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 35s 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<3s, are much less than normal time constants (~25s), and are similar to those observed in patients with peripheral vestibular lesions. Alexander's law also developed, on average, in 10s. We conclude that Alexander's law is not simply a consequence of non-reciprocal vestibular stimulation