In the 1960s, Ronald Melzak and Patricia Wall (1965) proposed the gate-control theory of pain, which states that the spinal column contains a neural gate that can be opened (allowing the perception of pain) or closed (blocking the perception of pain). The brain can send signals downward to the spinal cord to close the gate and thus suppress the sensation of pain.

The gate-control theory was proposed as an explanation for the effects of acupuncture, in which thin needles are inserted at specific points in the body to produce various effects, such as local anesthesia. The gate-control theory assumed that the presence of acupuncture needles somehow shuts the pain gate, inhibiting the experience of pain.

Imagine that you hit your thumb with a hammer. Pain pathways from the periphery of the body (thumb, foot, and so on) make a synaptic connection in the spinal cord and then ascend to the brain. However, a strong peripheral stimulus (as applied during acupuncture) can close this "gate" in the pain pathway. Also, signals coming down to the spinal cord from the brain (as during hypnosis or the excitement of athletic competition) can close the gate.

Note that the gate is not a physical structure that actually opens and shuts; rather, the gate is the inhibition of neural impulses. Neurotransmitters in the synapse between the pain cell and the gate cell are involved in gate control, but much is yet to be known about their identity.

Since the original conceptualization of gate-control theory, Wall and Melzack (1999) have revised it. They still believe that some pain originates in signals coming through the spinal cord gate, but they have now concluded that ultimately the brain generates the experience of pain.