Thinking the Hurt Away: Expectations hitch ride on pain’s brain pathway

When it comes to pain control, a dose of positive thinking goes a long way, according to researchers who have found that many of the same brain areas that respond to severe pain also respond to mere expectations of pain. This commonality provides a neural route for the mind to quell pain and could explain the pain-fighting power of placebos, the scientists say.

“Pain emerges from the interaction between signals coming from an injured body region and cognitive information unique to each individual, such as expectations about what that pain will feel like,” says neuroscientist Robert C. Coghill of Wake Forest University School of Medicine in Winston-Salem, N.C. He and his coworkers report their results in the Sept. 6 Proceedings of the National Academy of Sciences.

For their study, Coghill and his colleagues recruited 10 volunteers, ages 24 to 46, and fitted each with a device that delivered heat pulses to the lower right leg. In a training session, the researchers taught participants to expect one of three intensities of painful heat, depending on the delay between a tone and the jolt. A 7-second interval signaled heat that caused mild pain, a 15-second wait heralded heat that produced moderate pain, and a 30-second gap indicated heat resulting in pronounced pain.

Each heat pulse lasted for 20 seconds, and none burned or damaged the skin.

A day or two after training, each participant completed 30 heat-pulse trials while a functional magnetic resonance imaging scanner measured blood flow throughout the brain. On about one-third of the trials, the researchers switched the timing signals for upcoming pain amounts so that volunteers received heat pulses that were either of higher or lower intensity than they expected.

As the magnitude of expected pain increased, brain regions associated with learning, memory, emotion, and tactile sensation became more active. Areas of neural activation measured while volunteers actually experienced pain largely corresponded to areas activated by the expectation.

When participants received the most-painful heat after expecting only moderately painful jolts, the intensity of their self-reported pain fell by 28 percent compared with trials in which they both expected and experienced the severe pain.

These expectations of less pain yielded about as much relief from physical pain as researchers had previously reported for morphine, Coghill says. The new study adds to a growing body of evidence that placebos work via the brain mechanisms underlying pain (SN: 9/3/05, p. 157: Available to subscribers at Placebo reins in pain in brain).

In contrast, expectations of harsher heat pulses than were actually delivered didn’t magnify volunteers’ self-reported pain. The researchers plan to examine potential effects of negative expectations more closely in pessimists, whose personalities may predispose them to pain sensitivity.

The new report “underscores the biological fact that pain is not merely a passive response to tissue damage or potential tissue damage,” remarks neuroscientist Donald D. Price of the University of Florida’s College of Dentistry in Gainesville. “Its magnitude is partly determined by ongoing expectations.”

The work opens the door to exploring purely psychological interventions to prepare patients for painful medical treatments by recasting their expectations of what’s in store, Coghill notes.