Acupuncture can relieve wrist pain, and researchers have tracked the brain and nervous system changes that may help explain why.

Scientists randomized 80 people with mild or moderate carpal tunnel syndrome — pain caused by nerve compression at the wrist — to one of three groups. The first received acupuncture at the wrist and ankle. The second got acupuncture at the wrist alone. And the third received sham acupuncture, using “fake” needles near the affected wrist, as a placebo. Using functional M.R.I. and nerve conduction tests before and after the procedures, they measured the effect on brain and nerves.

All three groups found relief from pain, but both of the true acupuncture groups showed measurable physiological improvements in pain centers in the brain and nerves, while sham acupuncture did not produce such changes. Improvement in brain measures predicted greater pain relief three months after the tests, a long-term effect that placebo did not provide. The study is in Brain.

“What’s really interesting here is that we’re evaluating acupuncture using objective outcomes,” said the senior author, Vitaly Napadow, a researcher at Harvard. Sham acupuncture was good at relieving pain temporarily, he said, but true acupuncture had objective physiological — and enduring — effects.