Watching the brain under hypnosis

Yesterday, I told you about researchers who visualized the effects of stress on the human brain. Let's focus today on the activities of our brain during and after hypnosis.

Yesterday, I told you about researchers who visualized the effects of stress on the human brain. Let's focus today on the activities of our brain during and after hypnosis, with the help of the New York Times (Free registration, but permanent link). For example, you'll discover that "new experiments, which used brain imaging, found that people who were hypnotized 'saw' colors where there were none. This particular research has also been covered a few months ago by Nature and by Scientific American.

Let's start this overview by an introduction from Scientific American.

The word "hypnosis" tends to conjure up images of subjects partaking in silly activities they might not otherwise agree to. But over the past few decades, scientific study of hypnosis has begun to identify how the approach can work to alter processes such as memory and pain perception. According to a new report, hypnotic suggestions regulate activity in certain regions of the brain and can help it manage cognitive conflicts.

This new report was co-authored by Amir Raz, an assistant professor of clinical neuroscience at Columbia University, who works at the Brain Imaging Lab. Raz wanted to know how hypnosis could be used to reduce these cognitive conflicts and based the study on the Stroop test. The New York Times explains what is this test.

The probe, called the Stroop test, presents words in block letters in the colors red, blue, green and yellow. The subject has to press a button identifying the color of the letters. The difficulty is that sometimes the word RED is colored green. Or the word YELLOW is colored blue.
For people who are literate, reading is so deeply ingrained that it invariably takes them a little bit longer to override the automatic reading of a word like RED and press a button that says green. This is called the Stroop effect.

You can experiment this effect yourself. Below is an example taken from a series of optical illusions on display on the At-Bristol website. And here is a link to the page about the Stroop effect.

The Stroop effect

So how did Raz use this test?

Sixteen people, half highly hypnotizable and half resistant, went into Dr. Raz's lab after having been covertly tested for hypnotizability. The purpose of the study, they were told, was to investigate the effects of suggestion on cognitive performance. After each person underwent a hypnotic induction, Dr. Raz said:
"Very soon you will be playing a computer game inside a brain scanner. Every time you hear my voice over the intercom, you will immediately realize that meaningless symbols are going to appear in the middle of the screen. They will feel like characters in a foreign language that you do not know, and you will not attempt to attribute any meaning to them."

After giving these suggestions, Raz ended the hypnotic session and let several days go before using the fMRI (functional magnetic resonance imaging) technique on the sixteen participants who had to pass the Stroop test.

Not too surprisingly, the subjects who were easily influenced did not read the words and identified quickly the colors, while the other ones, resistant to hypnosis, tried to read the words and were confused.

When the brain scans of the two groups were compared, a distinct pattern appeared. Among the hypnotizables, Dr. Raz said, the visual area of the brain that usually decodes written words did not become active. And a region in the front of the brain that usually detects conflict was similarly dampened.

Below is one of these brain scans (Credit: Proceedings of the National Academy of Sciences, via Scientific American).

Brain under hypnosis

This research work about hypnosis has been published by the Proceedings of the National Academy of Sciences under the title "Hypnotic suggestion reduces conflict in the human brain" (Vol. 102, No. 28, Pages 9978-9983, July 12, 2005). Here is a link to the abstract.

Finally, what are showing these experiments? They basically tell us that hypnosis will work with easily influenced people who will then process information differently before and after having been hypnotized.

Sources: Sandra Blakeslee, The New York Times, November 22, 2005; Sarah Graham, Scientific American, June 28, 2005; and various web sites

You'll find related stories by following the links below.


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