Plasticity of Deep Brain Structures in Mild Cognitive Impairment and Healthy Aging

tTIS is an innovative non-invasive brain stimulation approach, in which two or more independent stimulation channels deliver high-frequency currents in the kHz range (oscillating at f1 and f1 + Δf). These high-frequency currents are assumed to be too high to effectively modulate neuronal activity. Still, by applying a small shift in frequency, they result in a modulated electric field with the envelope oscillating at the low-frequency Δf (target frequency) where the two currents overlap. The peak of the modulated envelope amplitude can be steered towards specific areas located deep in the brain, by tuning the positions of the electrodes and the current ratio across stimulation channels. Here, we applied tTIS via surface electrodes applying a low-intensity (2mA baseline to peak), sub-threshold protocol following the safety guidelines for low-intensity transcranial electric stimulation in humans.