LAUSR

Galvanic vestibular stimulation (GVS) is an electrical stimulation technique with electrodes placed on both mastoids that allow the perception of vestibular sensations to be evoked with excellent temporal control and without the need to accelerate the participant’s head. GVS, therefore, became one of the most frequently used tools in imaging studies investigating the vestibular system [1–3]. Additionally, it was used in various behavioral experiments [4–6] on the impact of vestibular stimulation on cognitive processes. Although GVS allows vestibular sensations to be evoked reliably, the applied protocols and stimuli varied significantly across the different experiments. Beside the waveforms, the current intensities, in particular, differed between the studies. In studies on posture or gait the currents tended to be in the range between 1 and 2 mA [7, 8], while in those on the cortical processing of vestibular input currents were usually greater and ranged from 2.0 mA up to 3.5 mA [9–11]. Recent works on the effect of noisy GVS [12, 13] typically applied currents between 50 and 500 μA which are considered sub-threshold stimulations. A recent study on stochastic resonance in the vestibular system used a sinusoidal GVS of varying amplitudes between 0 and 1.9 mA to demonstrate a noise-induced facilitation of vestibulospinal reflexes [14]. Given the increasing interest in GVS as a research tool and its possible advent in clinical applications (e.g., treatment of balance disorders such as bilateral vestibulopathy), little is known about the effect of the stimulation parameters on vestibular perception. Thus, the aim of the current study was to identify perceptional thresholds for DC boxcar-shaped GVS stimulations in healthy subjects (HS). Since the thresholds might be modulated by the orientation of the vestibular organ relative to the gravitational field, thresholds were estimated in upright sitting, as well as in supine body position. The perceptional vestibular thresholds were measured in 22 right-handed HS (mean age 27.8 years, SD 4.78 years; 12 male, 10 female) during GVS via a pair of electrodes attached bilaterally over the mastoids. Five HS were invited to participate in two additional sessions in which the test–retest reliability of the thresholds was investigated. Thresholds for the vestibular perception of boxcar-shaped stimuli were estimated for application durations of 500, 1000, and 2000 ms in randomized but balanced order for right cathodal and left cathodal stimulation. This procedure resulted in six different thresholds per subject (L500, R500, L1000, R1000, L2000, R2000). Every threshold was estimated in a run consisting of 20 stimulations of different intensities selected based on the Quest algorithm [15]. For the first stimulation a random current between 1.3 and 1.7 mA was chosen. The time between two stimulations was approximately 3 s and between two runs a pause of 1 min was performed. Ten HS were measured in a supine position, while the other twelve sat upright on a chair. All HS were asked to focus on vestibular perception and to ignore all other somatosensory sensations or possible muscle switching. Subjects reported an undirected experience of dizziness for above-threshold stimulation. The average thresholds for the 500, 1000, and 2000 ms stimulation were 1.79 mA This manuscript is part of a supplement sponsored by the German Federal Ministry of Education and Research within the funding initiative for integrated research and treatment centers.