Improvement of Memory in Mild Cognitive Impairment

tACS will be delivered by a battery-driven current stimulator Starstim SS32 (Neuroelectrics) through surface Ag/AgCl electrodes placed into holes of a neoprene cap corresponding to the international 10/20 EEG system. Gel (Parker Lab, Inc.) will be applied to optimize signal conductivity and lower impedance. Two tACS (active and sham) conditions will be applied in randomized order. 40 Hz tACS will be delivered to different brain areas of the memory network. We will employ a multielectrode montage based on electric field modeling using the individual MRI to optimally reach the target areas. The maximum injected current per electrode is 2mA and the overall maximal current is 4mA to generate an average electric field of 0.25 V/m.

EEG will be recorded with a 257-channel EEG system. An EEG net is applied at once on the head with evenly spaced sensors that provide full scalp coverage, including the cheek. The net contains Ag/Ag-Cl electrodes that are interconnected by thin rubber bands and contain small sponges soaked with saline water that touch the participant's scalp surface directly. Net application takes about 10 min to derive to impedances of \<30 kOhms. EEG is recorded with 1 kHz and band-pass filtered between DC-200 Hz. Vertex electrode Cz is used as an acquisition reference.

Clinical Evaluation and Cognitive Assessment - to characterize the level of dementia and changes in cognitive status measured at the baseline and after 4 weeks of gamma/sham tACS intervention, and in a follow-up 3 months after the stimulation using MoCA.