Introduction: Repetitive transorbital alternating current stimulation (rtACS) can improve visual deficits in patients with optic nerve damage. Recent retrospective results suggest that rtACS enhances oscillatory brain activity. The exact mechanisms of rtACS are unclear and little is known about possibly frequency-specific neural-plastic mechanisms. An association between bandwidth-confined neural-entrainment and vision recovery maximization could offer a novel therapeutic option for patients with optic neuropathy.
Objectives: The goal of this prospective open-label study was to investigate if the enhancement of rhythmic brain activity over 10 days of consecutive rtACS stimulation is associated with visual field recovery. The secondary goal was to investigate neurophysiological mechanisms related to frequency dependent adaptive plasticity.
Methods: 18 Patients with visual field impairments resulting from pre-chiasmatic partial optic nerve damage received rtACS on 10 consecutive days. Daily, subject-specific treatment parameters (<500 μA, 9-37 Hz, 25-40 min/day) were defined and EEG-spectra collected prior to and after rtACS. Visual field data was collected at day 1 and 10. The change of spectral-power in classic bandwidths were investigated and correlated with visual field deficit recovery.
Results: After 10 days of rtACS alpha-power over bilateral occipital electrodes was significantly larger than at baseline (F(Time x alpha-power)p < 0.01). This effect was progressive over subsequent days of stimulation (cubic-fit, R(2) 0.70, RMSE 0.008). Perimetric results improved significantly, but they were not associated with changes in alpha-synchronization.
Discussion: rtACS can induce cumulative bandwidth-confined changes in brain rhythms over multiple sessions. These findings are in line with the notion of brain-state dependent [1] and bandwidth-confined entrainment [2] as well as rtACS facilitated visual recovery [3].
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