By Catherine A. Sanderson, Amherst College
We experience pain when sensory neurons called nociceptors detect some kind of damage to the body. When they detect damage, they transmit signals to the spinal cord and brain. So, how do pain sensations get turned into perceptions and reach our conscious awareness? The most widely accepted explanation for how we perceive pain is the gate control theory.
The Influence of Psychology on Pain
Every year, about 800 people attempt to climb to the top of Mount Everest. By all accounts, even attempting this climb involves considerable physical pain. The oxygen levels at Base Camp are only 50% of what they are at sea level. The thinner atmosphere can also lead to snow blindness caused by inflammation of the cornea, as well as severe eye pain.
None of this sounds very pleasant. But many people are willing to undergo this pretty intense physical pain and pay as much as $100,000 to do so. Why? Because our experience of pain is heavily influenced by psychology.
As in all cases of perception, how we think about painful experiences matters, too. This is why many people voluntarily undergo things that are by all objective accounts painful: having ears pierced, getting a tattoo, giving birth, and, yes, climbing Mount Everest.
The Definition of Pain
The International Association for the Study of Pain defines pain as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage”. Medical professionals distinguish between acute pain and chronic pain.
Acute pain is intense but time-limited pain that is generally caused by tissue damage or disease: a broken bone, a cut or bruise, and childbirth. This type of pain typically disappears over time as the damage heals and lasts less than three months.
In contrast, chronic pain, which afflicts 20% to 30% of American adults, might begin as acute pain but it does not go away after a minimum of three months. But cases where pain persists despite tissue recovery suggest that psychological factors may play a role.
This article comes directly from content in the video series Introduction to Psychology. Watch it now, on Wondrium.
The Gate Control Theory
According to the gate control theory, when body tissues are injured, such as when you get cut or scraped, nerve endings in the damaged area transmit impulses to a particular part of the spinal cord. The nerve fibers that transmit sharp and localized pain sensations carry information very rapidly. The nerve fibers that transmit dull or aching pain carry information much more slowly, so it takes longer to experience some types of pain than others.
Once these nerve impulses reach the spinal cord, one of two things may happen. When the pain is not sufficiently intense, a gatekeeper in the spinal cord remains shut, so the pain sensations don’t travel to the brain. If the sensations are sufficiently intense, the gate is opened, and the nerve impulses are sent all the way up to the brain, where they are experienced as pain. The more signals that reach the brain, the more pain the person experiences.
These gates are controlled by chemicals—neurotransmitters. Some neurotransmitters, such as substance P and glutamate, open the gate, increasing pain. Other neurotransmitters, such as serotonin and endorphins, can close the gate, reducing pain. When the gate is open, pain sensations travel to the somatosensory cortex of the brain, which tells us exactly where on the body the pain is occurring.
The size of the area in the somatosensory cortex devoted to a particular region of the body helps determine how sensitive we are to pain experienced in that region.
Some Factors Can Lead to Fewer Pain Sensations
The gate control theory also proposes that a number of different factors can lead the gate to close, thereby blocking the transmission of pain signals to the brain. One way to shut the gate is to increase the stimulation of nerves at the site of the pain. This is why you immediately put your finger in your mouth after you burn it or grab your foot after stubbing your toe.
Additional stimulation such as pressure, heat, or cold pushes the nerve fibers that conduct most sensory signals to shut the gate, which stops the transmission of pain signals to the brain. It’s also why other ways of increasing stimulation—rubbing a leg cramp, scratching an itch, and putting an ice pack or hot water bottle on a sprained ankle—may all reduce pain.
But it’s not just physical stimulation that influences whether pain signals reach the brain; psychological factors also play a role. When a person is distracted or relaxed, the brain shuts the gate. Similarly, athletes in the heat of a game, and with high levels of adrenaline and flow, may experience a serious injury, such as dislocating a shoulder, but not be consciously aware of their injury at the time.
In this case, their psychological state may initially stop the transmission of pain signals, and they only consciously feel the pain later on. This is also why many of the strategies people use to manage pain involve distraction: listening to music while you exercise or watching a movie during a medical procedure.
Common Questions about the Gate Control Theory
The gate control theory states that when a part of the body is damaged, nerve endings at the injured site transmit impulses to a specific part of the spinal cord. When nerve impulses reach the spinal cord, two things can happen: If the injury isn’t intense, the gate in the spinal cord remains closed, and the pain signal is not transmitted to the brain. But if the injury is too severe, the gate opens, and the pain signal is transmitted to the brain, leading to experiencing the pain.
The gates are controlled by certain chemicals called neurotransmitters. For example, some neurotransmitters, such as serotonin and endorphins, do not allow the gate to open, reducing pain. On the other hand, some neurotransmitters such as glutamate and substance P cause the gate to open and thus increase the sensation of pain.
A number of different factors can cause the gate to close, thus preventing pain signals from being transmitted to the brain. One of these factors is to increase nerve stimulation at the site of pain. Putting a burnt finger in the mouth immediately after burning or pressing the pain spots are strategies that people do unconsciously to reduce pain.
