KELLY MCEVERS, HOST:
When you whack yourself with a hammer, it may feel like the pain is in your thumb. But really it's in your head. NPR's Jon Hamilton has this report on how the brain controls our perception of pain.
JON HAMILTON, BYLINE: Brain scientists have learned a lot about pain by studying people like Dwayne Turner. He was an Army combat medic in Iraq who received the Silver Star for valor. In 2003, Turner was unloading supplies when his unit came under attack. David Linden, a neuroscientist at Johns Hopkins School of Medicine, says Turner was wounded by a grenade.
DAVID LINDEN: He took shrapnel in his leg, in his side. And he didn't even notice that he had been hit.
HAMILTON: Turner began giving first aid and pulling other soldiers to safety. He was shot twice as he worked, one bullet breaking a bone in his arm. Yet Turner would say later that he felt almost no pain. Linden describes Turner's experience in his new book, "Touch: The Science Of Hand, Heart and Mind." He says there are lots of war stories like this.
LINDEN: Soldiers, in the heat of the moment, don't recognize the pain that's happening.
HAMILTON: But once that moment is over, those same soldiers may feel a lot of pain from something minor like a hypodermic needle. Linden says this is because the brain is constantly regulating our sensitivity to pain and every other touch sensation.
LINDEN: The brain can say, hey, that's interesting. Turn up the volume on this pain information that's coming in. Or it can say, oh no, let's turn down the volume on that and pay less attention to it.
HAMILTON: The brain also determines what emotion we attach to each painful experience. Linden says that's possible because the brain uses two different systems to process sensory information coming from our nerve endings.
LINDEN: One to determine the facts of pain - where is it on my body? What is its particular properties - stabbing, aching, burning and how intense is it? And then there is a completely separate system for the emotional aspect of pain - the part that makes us go, ow (ph), this is terrible.
HAMILTON: Linden says positive emotions can minimize pain. But negative emotions tend to have the opposite effect, something torturers have exploited for centuries.
LINDEN: If they want to accentuate pain during torture, they can do this with humiliation, with an unpredictable schedule of delivering pain. All of those things will make the emotional component of the pain experience stronger.
HAMILTON: A Senate report released late last year found that those were among the tactics used by CIA interrogators after 9/11. One thing scientists are still trying to understand is precisely how the brain regulates the perception of pain. Stephanie Jones from Brown University is part of a team that has found some clues.
STEPHANIE JONES: We looked at the part of the brain that responds to sensations in the hand.
HAMILTON: Specifically, Jones says, they looked at changes in low-frequency brain waves in that part of the brain. She says previous research had shown that these rhythms increase when the brain is blocking sensations in the hand.
JONES: And so they're filtering out in some way the distracting information so you can focus on the information that's important to the task at hand.
HAMILTON: But what controls these rhythms? Jones says the team suspected it was an area in the front part of the brain that helps us ignore distractions. To find out, she says, they monitored the brain waves of a dozen people given a specific task.
JONES: So in our study, we told them pay attention to your hand or pay attention to your foot.
HAMILTON: Sure enough, when people focused on their foot, low-frequency rhythms increased in the brain area that responds to hand sensations. But those low-frequency rhythms also increased in the brain area that ignores distractions, the team reports in The Journal of Neuroscience. Jones says those two areas became synchronized.
JONES: There's coordination between the front part of the brain, which is the executive control region of the brain, and the sensory part of the brain, which is filtering information from the environment.
HAMILTON: Jones says that suggests people can teach their brains to filter out things like chronic pain, perhaps through meditation. She says one study found that after eight weeks of mindfulness meditation, participants had much better control of the brain rhythms that block out pain. Jon Hamilton, NPR News.
NPR transcripts are created on a rush deadline by Verb8tm, Inc., an NPR contractor, and produced using a proprietary transcription process developed with NPR. This text may not be in its final form and may be updated or revised in the future. Accuracy and availability may vary. The authoritative record of NPR’s programming is the audio record.