The linear vestibulo-ocular reflex, locomotion and falls in neurological disorders

Issue title: Vestibular, Ocular Motor, and Locomotor Plasticity and Rehabilitation

Article type: Research Article

Authors: Liao, Ke | Walker, Mark F. | Joshi, Anand C. | Reschke, Millard | Strupp, Michael | Wagner, Judith | Leigh, R. John^;

Affiliations: Department of Neurology, Case Western Reserve University, Cleveland, OH, USA | Biomedical Engineering, Daroff-Dell'Osso Laboratory, Veterans Affairs Medical Center and University Hospitals, Case Western Reserve University, Cleveland, OH, USA | Neurosciences Laboratories, Johnson Space Center, Houston, TX, USA | University of Munich, Munich, Germany

Note: [] Corresponding author: R. John Leigh, M.D., Department of Neurology, 11100 Euclid Avenue, Cleveland, OH 44106-5040, USA. Tel.: +1 216 844 3190; Fax: +1 216 231 3461; E-mail: [email protected]

Abstract: Purpose: During locomotion, head perturbations, consisting of rotations and translations (linear movements), occur with predominant frequencies of 0.5–5.0 Hz. The vestibular reflexes act at short latency to safeguard clear vision and stable posture during locomotion. Much is known about the angular vestibulo-ocular reflex (aVOR) in response to head rotations, which depend on the semicircular canals of the vestibular labyrinth. However, the means to test reliably the linear or translational vestibulo-ocular reflex (tVOR), which depends on the otolithic organs, has only become available more recently. Methods: We used a moving platform to translate normal human subjects vertically at frequencies similar to those occurring during locomotion, under ambient illumination. Results: Our findings suggested that, whereas aVOR is concerned with stabilizing images of visual targets on the retina to optimize visual acuity, tVOR seems best suited to minimize retinal image motion between objects lying in different depth planes, in order to optimize motion parallax information. We then asked whether the tVOR functioned abnormally in patients with two neurological disorders that often cause falls: progressive supranuclear palsy (PSP) and cerebellar ataxia. We found that patients with PSP cannot adjust tVOR responses appropriately during viewing of near objects, nor converge their eyes. Vestibular-evoked myogenic potentials (VEMPs), an otolith-spinal reflex, are also impaired in PSP patients. Patients with cerebellar ataxia also lack the ability to adjust tVOR for near viewing, even though they may be able to converge. Conclusions: Taken together, our studies suggest that abnormal otolithic vestibular reflexes contribute to postural instability in PSP and cerebellar ataxia, and deserve further investigation.

Keywords: Locomotion, moving platform, motional parallax, PSP, cerebellar ataxia

DOI: 10.3233/RNN-2010-0507

Journal: Restorative Neurology and Neuroscience, vol. 28, no. 1, pp. 91-103, 2010