How the Brain Interprets Pain and How to Get Relief

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TweetNeuroscientists at Stanford University School of Medicine wanted to know whether the power of romance could overcome physical pain. They recruited 15 students who were early in an intense relationship and subjected their left hands to thermal pain—enough to hurt, but not to harm them. When the students focused on a photograph of the person they loved, they felt less of a burning sensation than when gazing at a picture of an equally attractive acquaintance. In their peer-reviewed, 2010 study, the researchers concluded that romantic feelings activated regions of the brain involved with endogenous opioids, the body's natural pain relievers, and dopamine, a neurotransmitter tied to cravings and rewards.

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The findings don't suggest people should seek out love affairs, notes Sean Mackey, chief of Stanford's pain management division. But they do indicate that engaging in "emotionally salient and rewarding experiences" can trigger the brain to provide relief, he says.

Since the brain is the epicenter of pain in the body, natural and medicinal strategies to relieve discomfort often focus there. For example, when you stub your toe, skin receptors send electrical signals through nerve fibers to the spinal cord and then up to the brain. Some of these fibers run like insulated telephone wires and carry the signals rapidly; others connect through web-like neural connections and travel more slowly.

In the case of a stubbed toe, the signals move rapidly up insulated nerve fibers to the brain's thalamus, which acts as a relay station and directs them to the sensory cortex. The signals are then interpreted by the brain as a sharp pain. The slower impulses, traveling through the web-like neural fibers, become a throbbing ache felt through the entire toe, a warning to treat the area gingerly while it heals.

As all this is happening, the brain also sends messages to the spinal cord that can amplify or dampen the pain. For example, a football player might jam his knee, but barely notice amid the excitement of a game. Most people can recall similar experiences, such as discovering bruises that they can't remember getting. These phenomena occur because of the brain's ability to filter out pain while the body engages in more urgent matters. Known as descending neural inhibitory control, it varies from person to person, says Andrea Trescot, a pain specialist in Jacksonville, Fla.

The brain's emotional control center, the limbic system, adds a second dimension, responding to how a person feels about pain or interprets its significance. David Kloth of Danbury, Conn., a pain specialist and spokesman for the American Society of Interventional Pain Physicians, notes that genetics, upbringing, and the cultural practices of various ethnic groups can all affect how pain is felt.

For example, Kloth says, people who were coddled as children by their parents every time they had small injuries may react strongly as adults to the slightest discomfort. This conditioning may contribute to the development of psychosocial problems such as anxiety, depression, or stress, which can amplify pain.

Temporary or acute pain, caused by minor ailments like a sprain or a burn, usually resolves itself after the affected region heals. When an acute situation goes unresolved or causes a malfunction in the nervous system, however, the pain cycle becomes self-perpetuating. In these cases, diagnosis and treatment can be challenging because the pain signals may reverberate throughout the nervous system, disguising the original source.

Mackey says research has shown that chronic pain should be viewed similarly to chronic diseases, like diabetes, since it likely will require the same kind of sustained, comprehensive treatment plan. But understanding and utilizing some of the options for activating the brain-nerve relationship remains central to the process:

The medicinal approach. While the goal should always be to find the root cause of pain, medication can be used to provide short-term relief. Different drugs address various aspects of the neural pathways and are effective in blocking pain signals from getting to the brain, says Charles Inturrisi, professor of pharmacology at Weill Cornell Medical College in New York City. These are the major categories:

•Anti-inflammatory medications, ranging from aspirin to nonsteroidal drugs and steroids, act on the nerves that detect pain on the periphery of the body. They generally succeed best with problems like osteoarthritis, where bones wear on each other, or an inflamed wound.
•Anti-seizure drugs may correct the spontaneous misfiring of sensory neurons, which can occur with herniated disks, headaches, or chronic regional pain syndrome, also known as CRPS.
•Antidepressants build up the brain's ability to block descending pain signals and work for many conditions involving nerve injury. (They do not require the person to be emotionally depressed.)
•Opioids and some synthetic narcotics tone down ascending sensations of pain and amplify descending inhibitory signals. Doctors use opioids with care. They can be addictive, since they activate the brain's ventral tegmental area, which is related to the limbic system and rewards people during pleasurable activities like eating or having sex. Opioids are most appropriate for acute pain, but may be used carefully with chronic pain, Trescot says.

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A homeostatic process. A form of medical acupuncture being practiced increasingly in the United States blends Chinese approaches, developed over 1,500 years, with a Western understanding of neurophysiology, says Gary Kaplan of McLean, Va., who is board-certified in medical acupuncture, family medicine, and pain medicine. Acupuncturists place fiber-thin needles at varying depths, often between ¼ and 2 inches, at carefully mapped points on the body, depending on the diagnosis. The needles arouse the nerves and release endorphins, which activate opioid receptors in the spinal column and brain, relieving the pain. Acupuncture stimulates the release of neurotransmitters, and the increase in their production seems to be progressive with long-term treatment. "It's a homeostatic process," says Kaplan. The goal is to bring the body back to its normal ability to self-heal.

Mind over matter. Research has shown that people can activate their descending pathways to block pain by distracting themselves with work, family, or hobbies they enjoy. Studies also have found that clinical hypnosis can help patients learn how to alter activity in specific areas of the brain, says Mark Jensen, a clinical psychologist and professor at the University of Washington Department of Rehabilitation Medicine. For example, hypnotic suggestions can reduce patient discomfort by decreasing activity in the anterior cingulate cortex, the area of the brain that processes the emotional response to pain. Such suggestions can also target the sensory cortex, which determines components of pain such as its intensity and what it feels like. A variety of disciplines are examining the use of hypnosis, which has been employed in dental procedures and studied as an aid to reduce pain in women with breast cancer.

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Stanford's Mackey is currently exploring how to teach patients to manage their own pain. In 2006 he used functional magnetic resonance imaging scans to successfully train patients to consciously increase or decrease activity in the regions of their brains that processed the pain they experienced. While the research continues, Mackey hopes the approach will eventually be refined sufficiently to allow for its widespread use.

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