Adaptation of Vestibular Tone Studied with Electrical Stimulation of Semicircular Canal Afferents
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JARO 14: 331–340 (2013) DOI: 10.1007/s10162-013-0376-1 D 2013 Association for Research in Otolaryngology
Research Article
Journal of the Association for Research in Otolaryngology
Adaptation of Vestibular Tone Studied with Electrical Stimulation of Semicircular Canal Afferents RICHARD F. LEWIS1,2,3, KEYVAN NICOUCAR1,2,4, WANGSONG GONG1, CSILLA HABURCAKOVA1,2, 1,2 AND DANIEL M. MERFELD 1
Jenks Vestibular Physiology Laboratory, Massachusetts Eye and Ear Infirmary, Boston, MA, USA
2
Otology and Laryngology, Harvard Medical School, Boston, MA, USA Department of Neurology, Harvard Medical School, Boston, MA, USA
3 4
Present Address: Service of Oto-Rhino-Laryngology, Head and Neck Surgery, University Hospital of Geneva, Faculty of Medicine, University of Geneva, Geneva, Switzerland Received: 19 September 2012; Accepted: 31 January 2013; Online publication: 20 February 2013
ABSTRACT Damage to one vestibular labyrinth or nerve causes a central tone imbalance, reflected by prominent spontaneous nystagmus. Central adaptive mechanisms eliminate the nystagmus over several days, and the mechanisms underlying this process have received extensive study. The characteristics of vestibular compensation when the tone imbalance is presented gradually or repeatedly have never been studied. We used highfrequency electrical stimulation of semicircular canal afferents to generate a vestibular tone imbalance and recorded the nystagmus produced when the stimulation was started abruptly or gradually and when it was repeatedly cycled on and off. In the acute-onset protocol, brisk nystagmus occurred when stimulation started, gradually resolved within 1 day, and reversed direction when the stimulation was stopped after 1 week. Repeated stimulation cycles resulted in progressively smaller nystagmus responses. In the slow-onset protocol, minimal nystagmus occurred while the stimulation ramped-up to its maximum rate over 12 h, but a reversal still occurred when the stimulation was stopped after 1 week, and repeated stimulation cycles did not affect this pattern. The absence of
Correspondence to: Richard F. Lewis & Department of Neurology & Harvard Medical School & Boston, MA, USA. Telephone: +1-6175733501; Fax: +1-617-5734154:email: [email protected]
nystagmus during the 12 h ramp of stimulation demonstrates that central vestibular tone can rebalance relatively quickly, and the reduction in the stimulation-off nystagmus with repeated cycles of the acute-onset but not the slow-onset stimulation suggests that dual-state adaptation may have occurred with the former paradigm but not the latter.
Keywords: vestibular, nystagmus, compensation, adaptation, electrical stimulation
INTRODUCTION The central vestibular system is highly plastic and can adapt to changes in peripheral labyrinthine inputs or changes in visually mediated demands. The former is typically studied with lesions of the labyrinth or vestibular nerve (e.g., Fetter and Zee 1988) that eliminate all input from the affected ear and produce substantial static and dyna
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