This is a question that we sometimes come across when discussing CES cranial electrotherapy stimulation. Firstly, the question itself is misleading. CES cranial electrotherapy stimulation does not shock the brain, it simply "triggers" the brain's response to balance certain hormones that are the main cause of anxiety, depression & insomnia. These hormones include: serotonin, melatonin & cortisol, among others.
There are three main common electrotherapy-type devices: TENS therapy, EMS electric muscle simulation and CES cranial electrotherapy stimulation. There are others as well, but these three are the most common for everyday treatment. They all function basically the same, sending an electrical current, at a given frequency, through wires that are then transmitted to the skin through electrodes (pads). In general terms, it's the frequency that causes the bodies reaction to the electrical current.
In the case of TENS therapy, the frequency sf very low, this effects the nerve endings and eliminates pain. For EMS electric muscle stimulation treatment, the frequencies are higher and penetrate deeper into the muscle tissue. This stimulates the muscles directly enabling them to strengthen.
CES cranial electrotherapy stimulation uses a very low frequency combined with an ultra-low current, this mild combination simply stimulates the brain enabling it to balance hormones as mentioned above, the StimTens MyoCalme CES device operates at a .5hz frequency. This ultra-low frequency is best for "all around" CES therapy treatment: relieving anxiety, treating depression and treating insomnia. When using for insomnia, it's best to use this approx. three hours before bed. There are other devices that operate at higher frequencies (100 hz) that can be used just before bed but they are not as effective for depression and anxiety treatment.