This device applies an electrical current to the brain to treat medical conditions. 

“The tiny electrical currents tDCS uses—generally one to two milliamps—cannot actually trigger the chemical impulse that crosses a synapse,” says American Scientific. “But some researchers believe tDCS strengthens synaptic connections to make learning more efficient. Small lab studies suggest it can improve vigilance and reaction times. 

Read more at: https://www.scientificamerican.com/article/do-diy-brain-booster-devices-work/.