Autonomic reflex referred to a set of normal reflexes that governed and regulated the abdominal organs.
In 2265, after being altered by the galactic barrier, Lieutenant Commander Gary Mitchell demonstrated to Doctor Elizabeth Dehner the ability to control his autonomic reflexes by causing a cessation of all of his biological processes (in effect, dying) for twenty-two seconds. She later reported to Captain James T. Kirk that she had observed Gary Mitchell controlling some of his autonomic reflexes. (TOS: "Where No Man Has Gone Before")