Decreased expectation of pain diminishes pain perception by 28%—more than a shot of morphine.
Not only do people who expect less pain report feeling less pain, but their brains respond similarly, with functional MRI (fMRI) showing less activation of pain-related areas, according to Tetsuo Koyama, M.D., Ph.D., and colleagues at Wake Forest University, Winston-Salem, N.C.
The team trained 10 healthy volunteers (aged 26–46 years) to associate tones of different durations with increasingly painful heat stimulation. (Proc. Natl. Acad. Sci. 2005;102:12950–5).
Subjects then underwent 30 trials that were monitored with fMRI. About a third of the time, the researchers mixed the signals, so that participants were expecting one temperature, but received a different one. When they expected moderate pain but received severe pain, all 10 subjects reported decreased pain intensity. Findings from fMRIs supported these perceptions, Dr. Koyama and associates said.
Expectations of decreased pain significantly reduced pain intensity-related brain activation; the severe pain evoked the same patterns as expected moderate pain.
“These data provide a neural mechanism that can, in part, explain the positive impact of optimism in chronic disease states,” the investigators wrote.