Acupuncture is the 2,000-year-old practice of sticking extremely thin needles into the skin at specific points on the body, to try to control a range of symptoms, including pain, allergies, and infertility. While its effectiveness is still under debate, some large-scale clinical trials suggest that the technique can effectively relieve pain.

Two large controlled trials of acupuncture for osteoarthritis pain, published in 2004 and 2005, found that the practice is more effective than a sham treatment. Another study, published in the New England Journal of Medicine in 2005, found acupuncture to be effective for migraines; however, patients experienced the same level of pain relief regardless of whether needles were placed in traditional acupuncture points or other spots.

"Acupuncture has been shown to have some therapeutic effect, but we have an incomplete understanding of the basic science that supports it," says Bruce Rosen, director of the Martinos Center for Biomedical Imaging, within the Harvard-MIT division of Health Sciences and Technology. Rosen and colleagues are part of a small number of scientists using brain-imaging techniques to understand what acupuncture does to the brain, as well as which characteristics, such as needle placement, are important for beneficial effects.

Rosen's team at the Martinos Center is funded in part by a $5.9 million grant to study the neurological basis of acupuncture from the National Center for Complementary and Alternative Medicine (NCCAM), a division of the National Institutes of Health in Bethesda, MD, whose mission is to rigorously test commonly used alternative therapies.

The team has shown that acupuncture affects regions of the brain involved with sensory processing, as well as with cognitive and emotional processing. For example, Kathleen Hui, an instructor at Harvard Medical School and a member of the Martinos team, has shown that acupuncture induces a characteristic activity pattern in the brain. Using functional magnetic resonance imaging, which measures brain activation, scientists found that parts of the limbic system, a brain area involved in emotion, motivation, and memory, and parts of the cortex, involved in cognitive processing, seem to quiet down during acupuncture. These areas become active when a person is focused on performing a task, suggesting that acupuncture might affect some homeostatic mechanism involved in the brain's resting state, says Rosen.

The Martinos researchers have also shown that acupuncture elicits the same characteristic pattern of brain activity, regardless of the type of acupuncture or placement of the needle, a finding that supports results from some clinical trials.

The team is now beginning to study the longer-term effects of acupuncture. Patients with carpal tunnel syndrome, a condition of pain or numbing in the wrist caused by a compressed nerve, show characteristic brain activity patterns in their somatosensory cortex, the brain area that processes sensory information. A pilot study by Vitaly Napadow, also at the Martinos Center, has found that after several weeks of acupuncture treatment, these patients' symptoms improve and their brain activation patterns begin to look more like normal subjects. "It's as if the [brain] changes that occur during carpal tunnel were somehow ameliorated during acupuncture," says Rosen.

Designing well-controlled trials is one of the biggest challenges in studying acupuncture. "With mood and pain, there are big placebo effects," says Chris Evans, a neurobiologist and pain expert at the University of California, Los Angeles. "To differentiate the placebo effect from the actual potential effects of acupuncture is an important goal to which imaging can probably add a lot."

However, scientists first need to figure out the best placebo treatments. With drug trials, doctors can simply give some patients a fake pill. "Because we don't know how acupuncture works, we can't develop an adequate sham," says Richard Hammershlag, a neurobiologist who began focusing on acupuncture several years ago, and is now research director at the Oregon College of Oriental Medicine in Portland.

Scientists sometimes use acupuncture needles placed outside of traditional acupuncture points -- but, according to Rosen's studies, that practice may resemble an active treatment more than a control. Another option is sham needles, which look like they are being inserted into the skin but don't actually penetrate. Rosen and his team hope their studies will eventually help to design optimal clinical trials.

"Only then," says Richard Nahin, NCCAM's senior advisor for scientific coordination and outreach, "can the scientific community provide definitive information to the public and health-care providers [on the effects of acupuncture]."