Discussion
nausea, itching, neurological and psychiatric disorders, headache, neurovegetative dysfunctions
MOTION SICKNESS, CORTEX
The primary aim of the current study was to verify the feasibility and efficacy of a noninvasive neuromodulatory technique as tACS of the vestibular cortex to reduce CS during VR experience, a very common users’ constellation of vestibular symptoms that are accompanied by disabling neurovegetative dysfunctions, in a real-life ecological setting.The results show that 10 Hz-tACS, if biophysically modelled to adequately target the vestibular cortex bilaterally, could represent a new strategy to reduce CS during VR performance in the majority of users (indeed, 67% of subjects improved their level of nausea during the ride with 10 Hz-tACS), regardless of the order in which subjects received the stimulation. The improvement in nausea is partly supported by the GSR results, which showed a divergent effect between 2-Hz tACS (increase) and 10-Hz tACS (decrease) on the autonomic system function, as expected due to the strong physiological links between vestibular and neurovegetative activity. However, 10-Hz tACS did not differ from sham, suggesting a possible dissociation between the improvement of nausea and the decrease in sympathetic activity. Future studies should consider investigating of other neurovegetative parameters such as pupillometry and heart rate variability to obtain more precise information on both sympathetic and parasympathetic activity. In order to better disentangle whether GSR activity is influenced by tACS, VR effects or a combination of both, additional control conditions should include measurements of GSR activity during VR immersion (without tACS) as well as tACS alone (without VR immersion) at different frequencies.The behavioural results cannot be explained by different side effects induced by the type of stimulation, as headache, itching and tingling scores were similar during stimulation at 2 Hz and 1 Hz. Only the discomfort score was marginally higher (see suppl. Mat., Fig. As there was no correlation between individual susceptibility to CS, as measured by the MSSQ-short questionnaire [However, as 10 Hz-tACS did not shorten the recovery time from the residual CS nausea, it should be considered only as an online CS countermeasure, at least when applied with the parameters of the current study. Further research is needed to verify whether prolonged tACS applications or repeated sessions of tACS during VR exposure (i.e. a kind of desensitisation approach) could lead to longer lasting improvements. It remains that other currently available strategies to reduce CS, such as self-controlled breathing [Beyond the training session, we did not use a baseline condition (i.e. without any tACS stimulation) to measure CS nor to test whether tACS alone could induce nausea, as this would have excessively prolonged the experimental time and has already been tested in a previous paper [NiBS techniques are increasingly being used as therapeutic procedures as an alternative or complementary to traditional pharmacological therapies for many neurological and psychiatric disorders, capitalising on the long lasting, predictable and safe [The rationale for using rTMS or tDCS to reduce vestibular symptoms is thought to be based on the induction of predictable changes in excitability [albeit via different mechanisms of stimulation-neural interaction of the two techniques [Clearly, potential applications of the current findings are relevant for several scenarios in which either cyber or motion sickness, which largely share common neural pathophysiological mechanisms [