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The power of suggestion lingers

June 27, 2005 By Roxanne Khamsi This article courtesy of Nature News.

Brain scans show hypnosis helps to focus the mind.

Therapists who swear that hypnosis can help their patients now have more evidence to back their claim. A study of brain-scan images shows that hypnosis can indeed alter cognitive activity after subjects have come out of the trance state, and that this can help them concentrate on certain tasks.

In a study published this week in the Proceedings of the National Academy of Science1, hypnotized subjects outperformed their peers at a classic test of mental focus. And scans pinpointed the area of the brain responsible for this lasting effect.

Hypnotists can strongly influence the behaviour of their subjects, sometimes helping them to give up addictive substances or, in tricks performed during stage performances, bark like a dog on hearing Elvis Presley. The findings indicate a biological basis for these types of behaviour, says Amir Raz at Weill Medical College of Cornell University, New York, the lead author of the study. "Words can form suggestions, and suggestions can have very, very strong effects on neurological activity," he says.

To study this effect, Raz used 16 volunteers, eight of whom were easily hypnotizable. These people would later be asked to tackle a mental challenge called the Stroop test, in which readers must name the colour in which a word is written. This is particularly tricky when the word is itself the name of a different colour. Participants should say ‘blue’, for example, when the word ‘red’ appears in blue ink.

In the hypnosis sessions, which lasted on average 25 minutes, Raz and his colleagues told the volunteers that when they later heard a cue, such as a coughing sound, they would see the printed words as gibberish and only be able to focus on the ink. Researchers then brought them out of their trance state, and 10 minutes later asked them to take the Stroop test while in a brain scanner.

Covert cough

The subjects who were suggestible to hypnosis completed the Stroop task 10% faster than their counterparts after this cue. Their brain scans showed that their anterior cingulate cortex, a region of the brain involved in planning and conflict resolution, had less activity compared with the non-hypnotized subjects. "Their anterior cingulate cortices were very quiet," says Raz.

This conflict-resolution centre struggles to reconcile various sensory and intellectual inputs. "Like when you see a cheesecake on the table and want to eat it, but remember that you can’t because your doctor told you that your cholesterol is high," says Raz.

Raz says the images help to prove that post-hypnotic suggestions have a real biological effect. "This was not social compliance, this was actually happening at the brain level," he says. It is unclear from this study whether hypnotic suggestion could help people with other tasks that require a different type of concentration.

"Science is finally catching up with what we have known but lacked the technology to prove," says Darlene Treese, president of the American Psychotherapy and Medical Hypnosis Association.

Raz speculates that hypnosis might not be strictly necessary to implant instructions in the minds of very susceptible people. Perhaps making repeated suggestions to them even when they’re not hypnotized might have the same effects on their brain, he says.


  1. Raz, A., Fan, J. & Posner, J. M. I. Proc. Natl. Acad. Sci Published online: doi:10.1073/pnas.0503064102 (2005).


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