Transcranial Electrical Stimulation (TES) is a non-invasive neurostimulation technique that  applies a specific, low-intensity current (usually 0-2 mA) to specific brain regions through  electrodes to modulate neural activity in the cerebral cortex. 

the goal of this technique includes a variety of stimulation methods, which can be divided into: 

Transcranial Direct Current Stimulation (tDCS) 

Transcranial Alternating Current Stimulation (tACS) 

Transcranial Random Noise Stimulation (tRNS) 

Transcranial pulsed current Stimulation (tPCS) 

Cranial Electrotherapy Stimulation (CES) 

Initially the technology was used to help patients with brain injuries such as strokes. Studies  in healthy adults have shown that transcranial electrical stimulation can improve cognitive  performance in a variety of tasks, such as language and math skills, attention, memory,  coordination, and problem-solving.