Minor adverse effects of galvanic vestibular stimulation in persons with stroke and healthy individuals

Objective: Galvanic vestibular stimulation (GVS) induces polarity-specific activations in the vestibular nerves and upstream in the vestibular and parietotemporal cortices as well as sub-cortical regions. This makes it an attractive technique for cognitive neuromodulation. However, systematic studies regarding adverse effects of GVS are unavailable. Thus, this study assessed adverse effects during and after sub-sensory GVS (mean: 0.6 mA) and GVS with 1.5 mA. Methods: Two hundred and fifty-five GVS sessions delivered to 55 persons with stroke and 30 healthy individuals were analysed using a 34-item-questionnaire including potential symptoms and rating scales for adverse effects. Results: The most frequent symptoms during and after GVS were slight itching (mean: 10.2%) and tingling (mean: 10.7%) underneath the electrodes. Healthy individuals and persons with stroke did not differ in their incidence and rated intensity of adverse effects, nor did persons with or without unilateral spatial neglect. Adverse effects were found more frequently with GVS with 1.5 mA as with sub-sensory GVS. Participants were unable to differentiate real from sham conditions during sub-sensory GVS. Importantly, neither seizures nor vertigo or nausea were observed. Conclusion: Sub-sensory GVS and GVS with 1.5 mA induce very few and mild adverse effects in healthy and persons with stroke and are safe when safety guidelines are followed.