Neuroimaging studies are helping hypnosis shed its 'occult' connotations by finding that its effects on the brain are real.

By Lea Winerman Monitor Staff Print version: page

Mention hypnosis, and for many people the image that comes to mind is a charlatan with a watch swinging back and forth, seducing otherwise sensible audiences into barking like dogs or clucking like chickens. Today, though, psychologists and others are using hypnosis to help patients stop smoking, lose weight or control pain. But despite this newfound respect for the method, scientists still aren't sure precisely how hypnosis–whether on stage or in a clinician's office–works.

For years, they've been trying to determine whether hypnotized people actually feel and see things differently than the nonhypnotized or whether the hypnotized give in to some combination of concentration and social pressure to follow hypnotists' demands.

Now, in the past decade or so and with the advent of neuroimaging technology like functional magnetic resonance imaging (fMRI), researchers have begun to get some answers.

Recent studies have found that when hypnotized people act on hypnotists' suggestions, their brains really do process information differently. When they're told to see colors, for example, the color-processing parts of their brains light up–despite the absence of any real color in front of them.

"This is an exciting time for us," says Columbia University psychologist and hypnosis researcher Amir Raz, PhD. "Neuroimaging technology allows us to really look at what's going on in the brain during hypnotic suggestion."

Now, Raz and others are beginning to branch out, to try to figure out why hypnosis works and why some people are more hypnotizable than others. They hope that their research will lead to not only a better understanding of a previously mysterious phenomenon, but also to more effective hypnosis treatments.

New findings

In one recent study, Raz found that he could use hypnosis to negate the Stroop effect, a task that demonstrates how attention processes can interfere with each other. In the task, participants view the names of colors printed in different colors of ink–for example, the word "red" printed in blue ink–and try to say the name of the ink color while ignoring the words. But people who are literate read the words automatically and so find the task difficult. They often respond slowly and mistakenly read the words rather than identify the ink color.

In a recent study, published in the Proceedings of the National Academy of Sciences (Vol. 102, No. 28, pages 9,978–9,983), Raz and his colleagues tested eight highly hypnotizable people and eight who weren't hypnotizable at all. The researchers performed a hypnotic induction, using methods such as guided imagery and visualization. Then, they told the participants that they would later see "meaningless symbols" printed in different colors of ink, and that when they did, they should press a computer key corresponding to the correct ink color.

Next, the researchers brought the participants out of hypnosis, put them in an fMRI machine and showed them the Stroop stimuli. But the hypnotizable patients who had been told that they'd see gibberish seemed, in fact, to see gibberish: They performed the task almost 10 percent faster than the nonhypnotized participants, and made fewer mistakes.

"It appears that these people were not playing games, and they were not acting," says Raz. "They were genuinely not reading the words."

The fMRI results were also striking. The hypnotizable participants showed less activity in an area called the anterior cingulate cortex, which is active when people are trying to resolve conflicting information from different sources–information like conflicting word names and colors.

Studies that have examined other types of hypnotic suggestions have found similar evidence. For example, Harvard psychologist Stephen Kosslyn, PhD, found that when he told hypnotized subjects that they would see gray-scale printed, Mondrian-like patterns in color, the participants showed activation in the same area of the brain–the right fusiform gyrus–as when they viewed actual color prints, according to a study published in theAmerican Journal of Psychiatry (Vol. 157, No. 8, pages 1,279–1,284). That area didn't light up, however, when the subjects weren't hypnotized and Kosslyn simply suggested that they visualize the drawings in color.

Another experiment found that hypnotically induced pain activated the same brain areas as "real" pain. In this 2004 study, published in Neuroimage (Vol. 23, No. 1, pages 392–401), University College London psychologist David Oakley, PhD, and his colleagues told eight highly hypnotizable participants that they would feel heat-related pain. They found that the same pain-processing areas of the brain–in the thalamus, anterior cingulate cortex and other areas–were active in those subjects as in subjects who actually touched a 120-degree metal probe. Subjects who simply imagined the pain, meanwhile, didn't show the same active brain areas.

The interpretation

The accumulating evidence suggests that people respond to hypnotic suggestion by actually "feeling" or "seeing" the suggested stimulus, be it pain or color.

The question that researchers have yet to answer, Oakley says, is how those changes come about. Scientists are still split on the issue: Some believe that hypnosis puts people into a trance state in which the brain behaves measurably differently than it does in other states. Others, meanwhile, believe that hypnosis is simply an intense form of concentration or focused attention.

So far, neuroimaging studies haven't been able to distinguish between the two. To do so, a researcher would need to find a difference in brain activity between a hypnotized and a nonhypnotized person–specifically, a difference unrelated to the effects of any particular suggestion such as seeing color, says University of Plymouth psychology professor Irving Kirsch, PhD.

"Nobody has yet disentangled the effect of suggestion from the effect of hypnotic induction," Kirsch says. "That's probably the next step."

In fact, he and Raz have begun to address the question with behavioral measures. In one study, published in February in Psychological Science (Vol. 17, No. 2), they repeated the Stroop experiment but this time included a condition in which they simply told the highly hypnotizable participants, who were not hypnotized at that time, that they would see gibberish rather than words.

The researchers found that, for these highly suggestible people, the suggestion alone was enough to improve performance on the task.

"We now have evidence showing that highly hypnotizable people do not need to be hypnotized in order to benefit from suggestion," Raz says. That indicates that hypnosis may be a normal state of consciousness rather than an altered state–and that some people who are particularly good at experiencing imaginative suggestions are the ones who can be hypnotized, Kirsch explains.

Meanwhile, researchers who believe that hypnosis alters the brain's functioning in some fundamental way say that the new findings don't negate that possibility. John Gruzelier, PhD, a psychologist at Imperial College in London, acknowledges that easily hypnotizable people are more suggestible even when not hypnotized. However, he says, the hypnosis itself still makes a difference.

"It's my feeling that we wouldn't bother going through the whole rigmarole of hypnosis if it was unnecessary," he says.

Raz and Kirsch hope that this and other work will also begin to help explain why some people are more highly hypnotizable than others, and will give researchers insight into who is most likely to benefit from hypnosis.