In the treatment of pain, motor points are selected from within the same neural segment adjacent to the area of pain. Other points are selected from the extremities where there are located the largest number of muscles. One of the most effective and widely used acupuncture points, Ho Ku, is located at the base of the thumb. The thumb, of all the digits and limb segments, has the largest cortical representation. Gaining scientific support is the theory that, in part, acupuncture works through the release of brain neurotransmitters.
Some evidence indicates that acupuncture induces a release of endorphins in the brain of humans.
Electrical stimulation has been found more effective than needle twirling. Stimulation must be sufficiently above the threshold of medium-sized fibers. Too strong a stimulus, however, serves to intensify pain. Treatment with acupuncture needles inserted deeply into muscle, as with electroacupuncture, is the most commonly used technique. With this the changes produced in the central nervous system seem to be sufficient to continue the beneficial effect long after the stimulation has ceased.