Gate Control Theory and the Brain

Gate Control Theory

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Researchers have long observed that factors such as thoughts, emotions, and expectations can influence our perceptions of pain. If you expect something to hurt, it probably will hurt worse. If you are upset or frightened, pain may seem more intense than it would if you were calm.

In order to explain why our mental states impact pain perceptions, researchers Ronald Melzack and Patrick Wall proposed what is known as gate control theory during the early 1960s. This theory suggests that the spinal cord contains a neurological "gate" that either blocks pain signals or allows them to continue on to the brain.

Unlike an actual gate, which opens and closes to allow things to pass through, the "gate" in the spinal cord operates by differentiating between the types of fibers carrying pain signals. Pain signals traveling via small nerve fibers are allowed to pass through while signals sent by large nerve fibers are blocked. Gate control theory is often used to explain the phantom or chronic pain.

How Gate Control Works

Following an injury, pain signals are transmitted to the spinal cord and then up to the brain. Melzack and Wall suggest that before the information is transmitted to the brain, the pain messages encounter "nerve gates" that control whether these signals are allowed to pass through to the brain. In some cases, the signals are passed along more readily and pain is experienced more intensely. In other instances, pain messages are minimized or even prevented from reaching the brain at all.

This gating mechanism takes place in the dorsal horn of the body's spinal cord. Both small nerve fibers (pain fibers) and large nerve fibers (normal fibers for touch, pressure, and other skin senses) both carry information to two areas of the dorsal horn. These two areas are either the transmission cells that carry information up the spinal cord to the brain or the inhibitory interneurons which halt or impede the transmission of sensory information.

Pain fibers impede the inhibitory interneurons, allowing pain information to travel up to the brain. Large fiber activity, however, excites the inhibitory neurons, which diminishes the transmission of pain information. When there is more large fiber activity in comparison to pain fiber activity, people tend to experience less pain. 

Melzack and Wall suggest that this process explains why we tend to rub injuries after they happen. When you bang your shin on a chair or table, for example, you might stop to rub the injured spot for a few moment. The increase in normal touch sensory information helps inhibit the pain fiber activity, therefore reducing the perception of pain.

Gate control theory is also often used to explain why massage and touch can be helpful pain management strategies during childbirth. Because the touch increases large fiber activity, it has an inhibitory effect on pain signals.

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Article Sources
  • Melzack R, & Wall PD (1965). Pain mechanisms: a new theory. Science (New York, N.Y.), 150 (3699), 971-9 PMID: 5320816