September 9, 2004
Brain scans show hypnosis at work
Trance impairs brain's ability to plan one's own actions.
by Michael Hopkin Nature News
From the BA Festival of Science, Exeter, UK.
A brain-imaging study has shed light on why some people are more susceptible than others to hypnosis. By hinting at the brain processes involved, the analysis also suggests that hypnosis - both the stage and therapeutic varieties - does have genuine effects on the brain's workings.
Those who are easily hypnotized show different activity in a brain region called the anterior cingulate gyrus, which is involved in planning our future actions, reports John Gruzelier of Imperial College London. In a hypnotic trance, the function of this region may be impaired, he says, meaning that subjects are more likely to follow a hypnotist's suggestion: "The hypnotist tells you to go with the flow, and so you don't evaluate what you're doing."This is consistent with the idea that those who are easiest to hypnotize tend to describe themselves as generally letting go of their inhibitions quite easily, Gruzelier told the British Association Festival of Science in Exeter, UK, on Thursday.
Some experts have argued that hypnotism is not a real physiological phenomenon at all, but rather the result of hypnotists imposing themselves on their subjects, who may be simply swept along. Stage hypnotists are often accused of intimidating their 'volunteers' into playing along for the sake of the show.
This effect is certainly part of the picture in performance hypnotism, says Gruzelier. "Lots of it is due to personality and persuasiveness, but then that's showbusiness," he told firstname.lastname@example.org. Such tactics can cause people to ignore the potential of genuine hypnosis to ease painful diseases, he adds: "Unquestionably, stage hypnotists give hypnotism a bad name."
"Humans like to comply; they don't like to be embarrassed," agrees Peter Naish, who studies hypnosis at the Open University in Milton Keynes, UK. But he insists that underneath the coercion used by charismatic stage acts, a physiological effect is occurring. "The evidence really is there; hypnosis is not miraculous," he adds.
Gruzelier studied 24 subjects, half of whom were categorized as succumbing easily to hypnotism, and half of whom were resistant. He scanned the volunteers' brains while they tackled a problem called the Stroop task, a test of mental flexibility that requires subjects to categorize a list of colours presented in a different colour - the word 'green' printed in blue, say - depending either on the name or the actual colour.
Gruzelier tested the subjects before and after they underwent a standard procedure used by hypnotists to put their subjects into a trance. In resistant subjects, the anterior cingulate gyrus was less strongly activated after the procedure than before, showing that their brains were working less hard as they got better at planning how to complete the task.But in hypnotized volunteers, the anterior cingulate, and the regions that govern it, were more strongly activated when they were in a trance, showing that they were struggling harder to plot their actions, Gruzelier reported. He suspects that this impaired ability to plan for oneself makes people more suggestible.
This process may underlie hypnotists' ability to influence their subjects' behaviour, be it stopping smoking or barking like a dog whenever they hear Elvis Presley. Subjects frequently report that they feel compelled to do something even though they know they don't really want to.
Gruzelier also suspects that hypnotism may interfere with subjects' evaluation of future emotions such as embarrassment. A region in the brain's medio-frontal cortex, close to the anterior cingulate, governs our perception of how we will feel if we take a certain course of action, he says. If connections between the two regions are impaired, stage volunteers might happily act without thinking.
That may well be the final weapon in the showbiz hypnotist's arsenal, says Gruzelier. By not only making volunteers suggestible but also taking away their sense of shame, the possibilities for public ridicule are immense. "The structure that monitors the emotional consequences of future actions becomes disconnected," he suggests. "So you make a fool of yourself."
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