Abstract
The vestibulo-ocular reflex (VOR) shows frequency-dependent behavior. This study investigated whether the characteristics of the electrically evoked VOR (eVOR) elicited by a vestibular implant, showed the same frequency-dependency. Twelve vestibular electrodes implanted in seven patients with bilateral vestibular hypofunction (BVH) were tested. Stimuli consisted of amplitude-modulated electrical stimulation with a sinusoidal profile at frequencies of 0.5, 1, and 2 Hz. The main characteristics of the eVOR were evaluated and compared to the “natural” VOR characteristics measured in a group of age-matched healthy volunteers who were subjected to horizontal whole body rotations with equivalent sinusoidal velocity profiles at the same frequencies. A strong and significant effect of frequency was observed in the total peak eye velocity of the eVOR. This effect was similar to that observed in the “natural” VOR. Other characteristics of the (e)VOR (angle, habituation-index, and asymmetry) showed no significant frequency-dependent effect. In conclusion, this study demonstrates that, at least at the specific (limited) frequency range tested, responses elicited by a vestibular implant closely mimic the frequency-dependency of the “normal” vestibular system.
Highlights
Bilateral vestibular hypofunction (BVH) is most often a chronic condition in which patients can suffer from blurred vision, impaired spatial orientation and postural instability (Brandt et al, 2010; van de Berg et al, 2011; Hain et al, 2013)
This study investigated whether the characteristics of the electrically evoked vestibulo-ocular reflex (VOR) elicited by a vestibular implant, showed the same frequency-dependency
Twelve electrodes at different anatomical locations were tested: four electrodes implanted in the vicinity of the superior ampullary nerve (SAN), three electrodes implanted in the vicinity of the lateral ampullary nerve (LAN) and five electrodes implanted in the vicinity of the posterior ampullary nerve (PAN)
Summary
Bilateral vestibular hypofunction (BVH) is most often a chronic condition in which patients can suffer from blurred vision (oscillopsia), impaired spatial orientation and postural instability (Brandt et al, 2010; van de Berg et al, 2011; Hain et al, 2013) These and other symptoms lead to an important decrease in physical activity, social functioning and vitality that dramatically impact the patients’ quality of life (Guinand et al, 2012; Ward et al, 2013). A vestibular implant, in a concept analogous to that of the cochlear implant, has been postulated as a possible therapeutic alternative This idea is currently investigated by research groups in Europe and the United States. Important efforts are undertaken to improve surgical techniques (Feigl et al, 2009; Dai et al, 2011a; Bierer et al, 2012; Rubinstein et al, 2012; van de Berg et al, 2012) and to solve biomechanical issues (Wall et al, 2003; Hayden et al, 2011; van de Berg et al, 2011; Fridman and Della Santina, 2013)
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