ECoG Power Alterations Across Stages of Prolonged Transcorneal Electrical Stimulation in the Blind Mice

Transcorneal electrical stimulation (TES) is a noninvasive approach for activating the retina and its downstream components through the application of electric current on the cornea. Although previous studies have demonstrated the clinical relevance of TES for modulating neurons with improvements in visual evoked potentials (VEPs) and electroretinograms (ERGs), there are still huge gaps in knowledge of its effect on the brain structures. To determine the short-term impact as well as the aftereffects of TES on neural oscillatory power in retinal degeneration mice, we performed electrocorticography (ECoG) recording in the prefrontal and primary visual cortices at different stages of prolonged TES [transient stage, following prolonged stimulation (post-stimulation stage 1) and long after the end of the retinal stimulation (post-stimulation stage 2)]) under varying stimulation current amplitudes (400 µA, 500 µA and 600 µA). The results revealed asymmetric differences between short-term and long-term pTES under different stimulation current amplitudes. Specifically, in post-stimulation stage 1 we observed significant increase in ECoG power of theta, alpha and beta oscillations respectively compared with baseline pre-stimulation results. These effects were dependent on the stimulation current amplitude and stimulation stage. Transient TES was not sufficient to cause significant changes in the ECoG power of all accessed oscillations except in medium, high and ultra-gamma oscillations which significantly decreased in 400 µA and 500 µA stimulation groups respectively compared with pre-stimulation results. Regarding long-term stimulation, the increase in ECoG power of theta, alpha and beta oscillations observed in post-stimulation stage 1 was significantly maintained in post-stimulation stage 2.Clinical Relevance- These results could be of core importance for human TES protocols suggesting that following pTES and long after the end of the stimulation, TES current amplitudes could have relatively different impacts on the power/activity of cortical oscillations. For example, by increasing the activity of oscillations that have been reported to inhibit irrelevant neural processes and enable the brain to focus on more relevant neural processes thus, inducing better coordination in the cortex.