The Gate Theory of Pain
In 1965 a theory called the 'Gate Theory of Pain' was produced, and for this idea, and others, Drs. Melzack and Wall won scientific acclaim. This theory was the first serious attempt to unify the many ideas that existed about the mechanism that perceives and transmits pain through the nervous system. The Gate Theory states that there are some specific nerve fibers that transmit pain to the spinal cord, whilst the input of other nerve fibers inhibits the transmission of pain. Both of these groups of fibers meet at a sort of 'micro-chip' in the spinal cord called the substancia gelatinosa.

The substancia gelatinosa is responsible for the integration of painful and pain inhibitory stimuli. If the pain input is excessive then pain is transmitted up the spinal cord, and the brain perceives it as pain. Pain fibers are probably the bare nerve endings found in the skin and other superficial tissues; they are easily stimulated and it would be an impossible situation if pain was experienced

every time we touched something. This theory proposes a balance between stimulation of the pain fibers and inhibition of that stimulus, so that pain is perceived only if the pain input overrides the inhibition of pain.

The only problem with this theory is that it does not explain fully the available facts. Acupuncture excites the pain inhibitory nerve fibers for a short period of time, thereby blocking pain, but the effects of acupuncture can last for some months after the acupuncture needle has been removed, and nothing in the Gate Theory really explains this prolonged effect. Acupuncture is a valuable treatment in a variety of non-painful diseases and the Gate Theory makes no attempt to explain the mechanism of acupuncture in the treatment of these diseases.

Another theory frequently proposed for acupuncture is that it represents a type of counter-pain. If pain is created in one part of the body then pain experienced in another part of the body is not noticed. This is a valid experimental model for short term relief of relatively mild pain, but again it does not explain the long-lasting effects of acupuncture in some types of severe pain.

Endorphins
The growing level of drug addiction in the West has provided a great stimulus for research into the mechanism of morphine action and addiction. Morphine-like substances have recently been discovered in the central nervous system. These substances are called endorphins, or naturally-occurring morphines,1 and they have been found to be very effective in blocking pain. Endorphins are released into the nervous system by the action of acupuncture and the effects of acupuncture anaesthesia can be reversed by the use of anti-morphine drugs.