Figure 1.

The six distinctive effects of GVS stimulation

(A) Square boxes indicate the GVS stimulus, and rounded boxes represent the corresponding neural responses from the vestibular afferent.

(B) Transient response patterns. Effect I: low-amplitude GVS stimulation increases and decreases firing rate with cathodic (blue) and anodic (red) current. Effect II: cathodic GVS stimulation can cause dramatic increases in firing rate of up to 2.5 spikes per second (sps) per μA. Data are presented as mean ± std. Effect III: GVS stimulation can maintain firing regularity (CV) while changing firing rate.

(C) Long duration adaptation. Effect IV: long-term GVS stimulation induces an immediate change in firing rate that adapts to a new baseline firing rate on the scale of seconds. In vivo (black) adaptation occurs with baseline offset in firing rate.

(D) Adaptation from different GVS-evoked baselines. Effect V: after a baseline of GVS stimulation, the afferent shows a smaller inhibitory response after and inhibitory (anodic) baseline and smaller excitatory response after an excitatory baseline.

(E) Responses to sinusoidal modulation. Effect VI: sinusoidal GVS modulation leads to increased/decreased firing rate in the cathodic/anodic half of a cycle with increased frequency of sine wave, and the neuronal response shows a phase lead for frequencies above 4 Hz that decreases to zero around 4–8 Hz.