Optimising electrical vestibular stimulation (EVS) for assessing vestibular function

Electrical vestibular stimulation (EVS) exhibits similar diagnostic performance to caloric irrigation for assessing interaural vestibular asymmetry. To optimise EVS for clinical uses, we investigated the influence of EVS stimulus parameters upon absolute torsional eye response amplitude and asymmetry assessments.

In young healthy adults (n = 72), monoaural sinusoidal EVS was delivered to each mastoid process for 40 s whilst ocular torsion was assessed. Ambient lights, electrode montage, and stimulus frequency were systematically manipulated.

Ambient lights (250 lx) attenuated torsional responses by 20 % compared to darkness. When the reference electrode was next to C7 (i.e., mastoid-C7 montage), responses to monoaural stimuli were 50 % those of binaural stimulation. Sinusoidal stimuli at 0.5 Hz evoked torsional responses 250 % larger than at 2 Hz but required 300 % more time to estimate asymmetry (12sec vs 4sec). Perceived discomfort was lower at 0.5 Hz than at 2 Hz. Pooled results (n = 53) suggest a normative asymmetry range of 0 ± 25 % for assessing pathological asymmetry.

Darkness and lower stimulus frequencies optimise absolute torsional eye response amplitude. Higher stimulus frequencies accelerate asymmetry assessments. To activate a single vestibular end organ, a mastoid-C7 (or mastoid-acromioclavicular) montage should be used.

These results extend the clinical potential of EVS for assessing vestibular function.