Brain Advance Access published online on April 22, 2003
Brain, doi:10.1093/brain/awg163
© 2003 by Guarantors of Brain
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Article
1 Department of Neurology, Klinikum Grosshadern, Ludwig-Maximilian's University, Munich, Germany
* Corresponding author. E-mail: Klaus.Jahn{at}lrz.uni-muenchen.de.
Received 23 December 2002
; revised 4 March 2003
; accepted 5 March 2003
To investigate age dependent changes we analysed torsional eye movement responses to binaural and monaural galvanic vestibular stimulation (GVS) in 57 healthy subjects (20-69 years old). GVS (1-3 mA) induced torsional eye movements consisting of static torsion toward the anode (amplitude 1-6°) and superimposed torsional nystagmus (slow phase velocity 0.5-3°/s, quick phase amplitude 0.5-2°, nystagmus frequency 0.75-1.5 s-1). Static ocular torsion and torsional nystagmus increased from the third to the sixth decade and decreased in older subjects, e.g. slow phase velocity increased from 1.5°/s (20-29 years) to 2.9°/s (50-59 years) and decreased to 2.5°/s for the seventh decade (60-69 years). Thus, an inverse U-shaped curve was found for the dependence of torsional eye movement responses on age. All structures relevant for vestibular function degenerate with age, but at varying times. Since hair cell loss precedes those seen in the vestibular nerve and Scarpa's ganglion, the decrease in hair cell counts could be compensated for by increased sensitivity of afferent nerve fibres or central mechanisms. Increased sensitivity could thus maintain normal function despite reduced peripheral input. As GVS acts at the vestibular nerve (thereby bypassing the hair cells), electrical stimulation should be more efficient in subjects with the beginning of hair cell degeneration, as seen in our data up to the sixth decade. The degeneration of nerve fibres, ganglion cells and central neurons becomes evident at older ages. Thus, the compensatory increase in sensitivity breaks down and GVS-induced eye movements decline--a finding that is reflected by the inverse U-shaped curve for age dependency presented in this study.
Keywords: galvanic vestibular stimulation; vestibular system; aging
Inverse U-shaped curve for age dependency of torsional eye movement responses to galvanic vestibular stimulation
2 Department of Neurology, Johannes Gutenberg University, Mainz, Germany
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