Transcranial electrical brain stimulation modulates the vestibular system

Transcranial electrical stimulation (tES) techniques are widely used to modulate brain excitability, though their mechanisms remain unclear. This study demonstrates that tES can directly activate the vestibular system, which may contribute to its observed effects. Using computational modelling, we showed that tES with a C3-Fp2 montage generates electric fields in the vestibular system, with strengths similar to those generated by electrical vestibular stimulation (EVS). Experiments in three participants with 4 Hz alternating current revealed that C3-Fp2 tES induces body sway at 4 Hz, comparable to the effect of EVS. A 2 mA tES produced a sway response equivalent to 1 mA EVS, suggesting both activate the vestibular system. These findings indicate that direct activation of the vestibular system may interfere with the interpretation of tES studies. The effect is likely to exist for wide range of typical tES frequencies and current intensities.