To date, there have been no reports of epilepsy induced by tDCS. In one study, MRI imaging was applied to observe the changes in the brain after 30 min and 1 h of tDCS stimulation in the safe mode, and it was found that there was no tissue edema, blood-brain barrier imbalance, or structural changes in the brain, and it was concluded that tDCS is a safe mode of transcranial stimulation. The same conclusion was confirmed in other studies.
The placement of the electrodes is crucial for the spatial distribution of the current and the direction of the current, determining the effectiveness of the stimulation. Commonly used stimulation electrodes have an area of 20-35 mm2, which is intended to minimize and focus stimulation on the area to be treated. On the other hand, a larger electrode area allows the current density to be reduced, thus ensuring the safety of the stimulation. Although the criteria for the stimulation parameters of tDCS have not been fully defined, it is generally accepted that a stimulation duration spanning 8-30 min and a DC current of 1.0-2.0 mA is safe and effective. Approximately 45% of the current is delivered to the skull and reaches the cortical surface. In addition, the current intensity should rise and fall slowly during tDCS treatment to avoid causing patient discomfort.