The vagus nerve, which supplies and regulates the gastrointestinal tract and digestion, is in the brain stem; its stimulation turns on the parasympathetic system and calms a person down. The brain stem also houses the reticular activating system (RAS), which regulates our level of arousal, influences our sleep-wake cycle, and can power up the rest of the brain (see Chapter 3 for details). Stimulation of the vagus and the RAS, Yuri believes, is the reason most patients who use the device have found they sleep better at night and are more awake during the day.
