June 26, 2018

ALL IN YOUR HEAD:

The Neuroscience of Pain: Brain imaging is illuminating the neural patterns behind pain's infinite variety. (Nicola Twilley, Mar. 3rd, 2018, The New Yorker)

It was toward the end of her fellowship in Boston that Tracey first began thinking seriously about pain. Playing field hockey in her teens, she'd had her first experience of severe pain--a knee injury that required surgery--but it was a chance conversation with colleagues in a pain clinic that sparked her scientific interest. "It was just one of those serendipitous conversations that you find yourself in, where this whole area is opened up to you," she told me. "It was, like, 'God, this is everything I've been looking for. It's got clinical application, interesting philosophy, and we know absolutely nothing.' I thought, Right, that's it, pain is going to be my thing."

By then, Tracey had been recruited to return home and help found the Oxford Centre for Functional Magnetic Resonance Imaging of the Brain. Scientists had already largely given up on the idea of finding a single pain cortex: in the handful of fMRI papers that had been published describing brain activity when a person was burned or pricked with needles, the scans seemed to show that pain involved significant activity in many parts of the brain, rather than in a single pocket, as with hearing or sight. Tracey's plan was to design a series of experiments that picked apart this larger pattern of activity, isolating different aspects of pain in order to understand exactly what each region was contributing to the over-all sensation.

In 1998, while her lab was being built, she took her first doctoral student, a Rhodes Scholar named Alexander Ploghaus, to Canada, their scientific equipment packed in their suitcases, to use a collaborator's MRI machine for a week. Their subjects were a group of college students, including several ice-hockey players, who kept bragging about how much pain they could take. While each student was in the scanner, Tracey and Ploghaus used a homemade heating element to apply either burns or pleasant heat to the back of the left hand, as red, green, and blue lights flashed on and off. The lights came on in a seemingly random sequence, but gradually the subjects realized that one color always presaged pain and another was always followed by comfortable warmth. The resulting scans were striking. Throughout the experiment, the subjects' brain-activity patterns remained consistent during moments of pain, but, as they figured out the rules of the game, the ominous light began triggering more and more blood flow to a couple of regions--the anterior insula and the prefrontal cortices. These areas, Tracey and Ploghaus concluded, must be responsible for the anticipation of pain.

Showing that the experience of pain could be created in part by anticipation, rather than by actual sensation, was the first experimental step in breaking the phenomenon down into its constituent elements. "Rather than just seeing that all these blobs are active because it hurts, we wanted to understand, What bit of the hurt are they underpinning?" Tracey said. "Is it the localization, is it the intensity, is it the anticipation or the anxiety?" During the next decade, she designed experiments that revealed the roles played by various brain regions in modulating the experience of pain. She took behavioral researchers' finding that distraction reduces the perception of pain--as when a doctor tells a child to count backward from ten while receiving an injection--and made it the basis of an experiment that showed that concentrating on a numerical task suppressed activity in several regions that normally light up during pain. She examined the effects of depression on pain perception--people suffering from depression commonly report feeling more pain than other people do from the same stimulus--and demonstrated that this, too, could change the distribution and the magnitude of neural activity.

One of her most striking experiments tested the common observation that religious faith helps people cope with pain. Comparing the neurological responses of devout Catholics with those of atheists, she found that the two groups had similar baseline experiences of pain, but that, if the subjects were shown a picture of the Virgin Mary (by Sassoferrato, an Italian Baroque painter) while the pain was administered, the believers rated their discomfort nearly a point lower than the atheists did. When the volunteers were shown a secular painting (Leonardo da Vinci's "Lady with an Ermine"), the two groups' responses were the same. The implications are potentially far-reaching, and not only because they suggest that cultural attitudes may have a neurological imprint. If faith engages a neural mechanism with analgesic benefits--the Catholics showed heightened activity in an area usually associated with the ability to override a physical response--it may be possible to find other, secular ways to engage that circuit.

Tracey's research had begun to explain why people experience the same pain differently and why the same pain can seem worse to a single individual from one day to the next. Many of her findings simply reinforced existing psychological practices and common sense, but her scientific proof had clinical value. "Countless people who work in cognitive behavioral therapy come up at the end of talks or write to me," Tracey told me. "They say how helpful it has been to empower their education of the patient by saying that, if you're more anxious about your pain, or more sad, look, here's a picture telling you it gets worse."

Posted by at June 26, 2018 4:30 AM

  

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