“Hypnosis is the oldest Western form of psychotherapy, but it’s been tarred with the brush of dangling watches and purple capes,” said Spiegel, who holds the Jack, Samuel and Lulu Willson Professorship in Medicine. “In fact, it’s a very powerful means of changing the way we use our minds to control perception and our bodies.”

Despite a growing appreciation of the clinical potential of hypnosis, though, little is known about how it works at a physiological level. While researchers have previously scanned the brains of people undergoing hypnosis, those studies have been designed to pinpoint the effects of hypnosis on pain, vision and other forms of perception, and not the state of hypnosis itself.

“There had not been any studies in which the goal was to simply ask what’s going on in the brain when you’re hypnotized,” said Spiegel.

Finding the most susceptible

To study hypnosis itself, researchers first had to find people who could or couldn’t be hypnotized. Only about 10 percent of the population is generally categorized as “highly hypnotizable,” while others are less able to enter the trancelike state of hypnosis. Spiegel and his colleagues screened 545 healthy participants and found 36 people who consistently scored high on tests of hypnotizability, as well as 21 control subjects who scored on the extreme low end of the scales.

Then, they observed the brains of those 57 participants using functional magnetic resonance imaging, which measures brain activity by detecting changes in blood flow. Each person was scanned under four different conditions — while resting, while recalling a memory and during two different hypnosis sessions.

“It was important to have the people who aren’t able to be hypnotized as controls,” said Spiegel. “Otherwise, you might see things happening in the brains of those being hypnotized but you wouldn’t be sure whether it was associated with hypnosis or not.”

Brain activity and connectivity

Spiegel and his colleagues discovered three hallmarks of the brain under hypnosis. Each change was seen only in the highly hypnotizable group and only while they were undergoing hypnosis.

First, they saw a decrease in activity in an area called the dorsal anterior cingulate, part of the brain’s salience network. “In hypnosis, you’re so absorbed that you’re not worrying about anything else,” Spiegel explained.

It’s a very powerful means of changing the way we use our minds to control perception and our bodies.

Secondly, they saw an increase in connections between two other areas of the brain — the dorsolateral prefrontal cortex and the insula. He described this as a brain-body connection that helps the brain process and control what’s going on in the body.

Finally, Spiegel’s team also observed reduced connections between the dorsolateral prefrontal cortex and the default mode network, which includes the medial prefrontal and the posterior cingulate cortex. This decrease in functional connectivity likely represents a disconnect between someone’s actions and their awareness of their actions, Spiegel said. “When you’re really engaged in something, you don’t really think about doing it — you just do it,” he said. During hypnosis, this kind of disassociation between action and reflection allows the person to engage in activities either suggested by a clinician or self-suggested without devoting mental resources to being self-conscious about the activity.

Treating pain and anxiety without pills

In patients who can be easily hypnotized, hypnosis sessions have been shown to be effective in lessening chronic pain, the pain of childbirth and other medical procedures; treating smoking addiction and post-traumatic stress disorder; and easing anxiety or phobias. The new findings about how hypnosis affects the brain might pave the way toward developing treatments for the rest of the population — those who aren’t naturally as susceptible to hypnosis.

“We’re certainly interested in the idea that you can change people’s ability to be hypnotized by stimulating specific areas of the brain,” said Spiegel.

A treatment that combines brain stimulation with hypnosis could improve the known analgesic effects of hypnosis and potentially replace addictive and side-effect-laden painkillers and anti-anxiety drugs, he said. More research, however, is needed before such a therapy could be implemented.

The study’s lead author is Heidi Jiang, a former research assistant at Stanford who is currently a graduate student in neuroscience at Northwestern University.

Other Stanford co-authors are clinical assistant professor of psychiatry and behavioral sciences Matthew White, MD; and associate professor of neurology Michael Greicius, MD, MPH.

The study was funded by the National Center for Complementary and Integrative Health (grant RCIAT0005733), the National Institute of Biomedical Imaging and Bioengineering (grant P41EB015891), the Randolph H. Chase, M.D. Fund II, the Jay and Rose Phillips Family Foundation and the Nissan Research Center.

Stanford’s Department of Psychiatry and Behavioral Sciences and Department of Neurology and Neurological Sciences also supported the work.