Transcranial Alternating Current Stimulation Reduces Network Hypersynchrony and Persistent Vertigo.

OBJECTIVES

Persistent oscillating vertigo that occurs after entrainment to periodic motion is known as Mal de Débarquement Syndrome (MdDS). Down-modulation of this oscillating vertigo is associated with reduction in long-range resting-state functional connectivity between fronto-parieto-occipital regions. In order to determine the association between this oscillating vertigo and hypersynchrony as measured by the auditory steady-state response (ASSR), we investigated the differences in ASSR between individuals with MdDS and healthy controls as well as the change in ASSR in individuals with MdDS before and after treatment with transcranial alternating current stimulation (tACS).

MATERIALS AND METHODS

Individuals with treatment refractory MdDS lasting at least six months received single administrations of fronto-parieto-occipital tACS in an "n-of-1" double-blind randomized design: alpha-frequency in-phase, alpha-frequency antiphase, and gamma frequency antiphase control. The treatment protocol that led to the most acute reduction in symptoms and improved balance was administered for 10-12 sessions given over three days (each session 20-min at 2-4 mA).

RESULTS

Twenty-four individuals with MdDS participated (mean age 53.0 ± 11.8 years [range: 22-66 years, median: 57.0 years]; mean duration of illness 38.6 ± 53.4 months [range: 6-240 months, median: 18.0 months]). Individuals with MdDS had elevated ASSR compared to healthy controls at baseline (t  = 5.95, p < 0.001). There was a significant decrease in the 40 Hz-ASSR response between responders compared to nonresponders to tACS (t-test, t  = -2.26, p = 0.04). Both in-phase and anti-phase alpha tACS lead to symptom improvement but only antiphase alpha-tACS led to a significant decrease of 40 Hz-ASSR (t-test, t  = -9.6, p < 0.001).

CONCLUSIONS

Our findings suggest that tACS has the potential to reduce network-level hypersynchrony and pathological susceptibility to entrainment by sensory input. To the best of our knowledge, this is the first successful demonstration of desynchronization by noninvasive brain stimulation leading to reduced vertigo. Other disease states associated with pathological functional coupling of neuronal networks may similarly benefit from this novel approach.