Cortical Electric Fields Differences in Transcranial Electrical Stimulation Protocols

Transcranial electrical stimulation (tES) is a term for a series of non-invasive and painless neuromodulatory techniques that uses a weak current (1-2mA) injected via two or more electrodes placed on the scalp that leads to changes in neuronal excitability for recovery of brain functions, improvement of cognitive processes, or treatment of major depression disorders TES includes transcranial alternating current stimulation (tACS) in which the injected alternating current synchronizes the periodic activity of the cerebral cortex. Ideally, acting on the desired target is necessary, but the electric current is spread on the brain depending on the electrode's size and positioning and the anatomical structures of the brain and non-brain tissues. Unavoidably, the current intensity is higher near the electrodes and decreases at deeper locations resulting in co-simulations Recently, two alternating currents with slightly different frequencies have been applied from electrodes attached to the scalp, known as temporal transcranial interferential stimulation (tTIS) It is argued that these currents interfere with each other and generate an interferential current on deep focal areas. However, stimulation optimization continues to be a problem considering the variability of the stimulus intensity among subjects explaining different clinical results.