Aug. 1, 2005
Hypnotic suggestion can reduce conflict in human brain
A new study using an old, misunderstood technique -- hypnotic suggestion -- finds the brain can override responses experts have long assumed to be ingrained and automatic, such as reading.
The study's publication in the July 12 issue of Proceedings of the National Academy of Sciences (PNAS) is remarkable for two reasons: first, it provides compelling evidence that humans can "unlearn" an automatic process, and, second, it points to hypnotic suggestion as a powerful new tool for brain research, generally.The study focuses on the Stroop Test -- a hallmark of attentional research that asks people to simply name the ink color a word is printed in.
But there's a trick to the test: the word "Red" might be printed in green ink. This immediately sets up a cognitive conflict within the brain, which is inclined to answer what it reads ("Red"), even though it knows the correct answer is "green."
"Thousands of studies have found that Stroop interference is difficult to overcome under conventional conditions, because reading is so ingrained," said Dr. Amir Raz, who led the research while a Research Fellow of Psychology in Psychiatry at Weill Medical College of Cornell University's Sackler Institute for Developmental Psychobiology, in New York City. Dr. Raz is now Assistant Professor of Clinical Neuroscience at Columbia University and the New York State Psychiatric Institute.
"We've always thought of the Stroop effect as almost automatic, and that's why this study is so important," he said. "Watching a participant's brain activity using both event-related potentials (ERP) and functional MRI (fMRI) during the Stroop test, we could see that not only was the brain's conflict-resolution center turned off as a result of hypnotic suggestion, but also those areas of the brain that may be involved in recognizing written words," Dr. Raz said.
The findings suggest that Stroop interference is not the automatic, immutable process experts have hitherto assumed it to be.
"This means that, using suggestion -- in this case post-hypnotic suggestion -- we were able to 'un-ring ' Pavlov's bell," Dr. Raz said.
In the study, Dr. Raz and co-researchers Drs. Jin Fan and Michael Posner used standard tests to identify healthy, "highly suggestible" individuals (experts believe that about 10-15 percent of us are particularly susceptible to hypnotic suggestion).
These individuals first took the Stroop test in practice sessions. Then, under ERP and fMRI observation, the participants underwent hypnotic induction. During this condition, Dr. Raz told participants that "Every time you hear my voice talking to you…you will immediately realize that meaningless symbols will appear in the middle of the screen."
"In other words, the symbols were placed in a special context where the simple English words 'Red' or 'Blue' in the Stroop test appeared as gibberish," Dr. Raz said.
The result: The Stroop effect disappeared. The power of suggestion essentially "de-automatized" the participant's reading response, causing them to view the words in the way a pre-lingual child or non-English-speaker might.
This removed the essential conflict that usually occurs within the brain during the Stroop test, allowing participants to identify the color of the characters on the screen as efficiently as if they were simple blocks of color.
"What's more, fMRI showed activity in exactly those brain regions important to the test – centers of attention like the anterior cingulated cortex and areas thought to relate to processing of visual word-form in the brain's occipital region," Dr. Raz said.
Another novel aspect of the study hinges on its design. "Instead of manipulating the task without addressing the participants, we manipulated the participants (i.e., with and without suggestion) while keeping the classic Stroop test pristine," Dr. Raz said. "This type of experimental design is common in social psychology experiments but not in cognitive neuroscience. Here we show that the 'social psychology ' approach can be very viable for brain research -- another testament to the inter- and multi-disciplinary nature of contemporary cognitive neuroscience."
Besides putting a dent in the inviolability of the Stroop effect, the findings may have implications for research into other areas of suggestion and attention.
"For example, the placebo effect – the ability of our brain and body to work on the mere suggestion that a pill might help us," Dr. Raz pointed out.
"It also speaks, literally, to psychotherapy and the power of the spoken word. It means that words -- talking to someone -- can create profound brain changes. This seems to be a top-down effect that may be able to override a whole range of impulses," he said.
The study's publication in PNAS is also a milestone in the rehabilitation and validation of hypnosis and hypnotic suggestion as a scientific tool.
"Hypnotic suggestion has too long been the subject of myth and misunderstanding, based on Hollywood depictions and stage shows," Dr. Raz said. "But we've known for a long time that hypnosis and attention are connected. And, in this study, we show that a specific form of hypnotic suggestion is capable of targeting focal functional brain areas – something no current drug can do. I believe that when used responsibly and judiciously, hypnosis can be a great tool, not only to advance scientific inquiry but perhaps even for treatment in certain psychopathologies."
It is also likely to afford a deeper understanding of consciousness itself, he said. "By isolating specific brain areas, suggestion allows us to learn more about processes that are at the forefront of consciousness and awareness -- what's happening when we dissociate, reflect, and introspect. Who we are."
Dr. Raz's work was funded in part by a grant from the DeWitt Wallace-Reader's Digest Research Fellowship in Psychiatry.
Co-author Dr. Posner, Adjunct Professor of Psychology in Psychiatry at Weill Cornell and former Director of the Sackler Institute, is currently at the University of Oregon, Eugene. Co-author Dr. Fan is currently at Mount Sinai School of Medicine, New York City.
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