Alpha-Sync; a prospective randomized controlled non-invasive alternating current stimulation study in patients with optic neuropathy

Introduction: Neuroplasticity is the ability of the nervous system to change structurally and functionally as a result of neuronal activity. Repetitive transorbital alternating current stimulation (rtACS) can simulate neuronal activity and entrain rhythmic brain activity in healthy subjects and improve visual field size in patients with optic nerve damage. Prosepctive randomized controlled studies are necessary to provide evidence of clinical efficiency. Methods: Electroencephalographic (EEG) power spectra were assessed to determine the association between days of stimulation and changes in alpha-activity over the occipital cortex in 37 patients with visual field impairments resulting from prechiasmatic partial optic nerve damage were included in a randomized controlled trial (RCT). The experimental group (n=19) received rtACS on 10 consecutive days. rtACS was given for 20–40 min/day. Treatment parameters were defined daily by subject specific alpha (lower cut-off) and flicker-fusion frequency (upper cut-off). The control group (n=18) received subliminal stimulation. Visual fields were collected at day 1, day 10, five days and two months after treatment. EEG alpha-power spectra were collected as well on all that days. Changes in alpha-power were associated with changes of activity in the visual fields. Results: The Intent-to-treat analysis indicates enhancement of alpha-power over the occipital, temporal and pareital electrodes. Visual field deficits were reduced. Conclusions: We argue that rtACS entrains alpha-oscillatory brain activity and promotes restoration after a circumscribed chronic pre-chiasmatic optic nerve lesion as assessed both by objective EEG changes and improvements of visual deficits in perimetry. Results suggest that effects of entrainment outlast the duration of stimulation and are enhanced by daily repetition as compared to placebo-stimulation in line with the notion of adaptive plastictic processes.