Modulation of visually induced self-motion illusions by alpha transcranial electric stimulation over the superior parietal cortex
Growing popularity of virtual reality systems has led to a renewed interest in understanding the neurophysiological correlates of the illusion of self-motion (vection), a phenomenon that can be both intentionally induced or avoided in such systems, depending on the application. Recent research has highlighted the modulation of power oscillations over the superior parietal cortex during vection, suggesting the occurrence of inhibitory mechanisms in the sensorimotor and vestibular functional networks to resolve the inherent visuo-vestibular conflict. The present study aims to further explore this relationship and investigate whether neuromodulating these waves could causally affect the quality of vection. In a crossover design, 22 healthy volunteers received 13 minutes of high-amplitude, focused -tACS over the superior parietal cortex while experiencing visually induced vection triggered by optokinetic stimulation. The tACS was tuned to each participants individual peak frequency, with {theta}-tACS and sham stimulation serving as controls. Overall, participants experienced better quality vection during -tACS compared to control {theta}-tACS and sham stimulations, as quantified by the intensity of vection. The observed neuromodulation supports a causal relationship between parietal oscillations and visually induced self-motion illusions, with their entrainment triggering over-inhibition of the conflict within the sensorimotor and vestibular functional networks. These results confirm the potential of non-invasive brain stimulation for modulating visuo-vestibular conflicts, which could help to enhance the sense of presence in virtual reality environments.