What Part of the Brain Is Affected by Hypnosis?
Hypnosis, or trance, is an altered state of mind in which a person is highly responsive to suggestion 1. While in trance, a hypnotic subject is focused entirely on certain ideas to the exclusion of all others. At one time, the hypnotic effect was widely believed to be an act of trickery or mysticism. However, in recent years, advances in cognitive science have found trance to be a natural state, grounded in the principle workings of the mind.
Induced by a hypnotist, hypnotic convincers are unusual physical phenomena for validating the process to his subject. One such feat is brought about by instructing the subject that a hand, arm, foot or other body part is becoming extremely heavy. Eventually the hypnotist will bid his client to try to lift that part of the body. To the subject's surprise, she cannot.
Yann Cojan, researcher at the University of Geneva in Switzerland, authored a study that viewed the mental activity of 12 volunteers experiencing hand paralysis while under hypnosis. It was discovered that activity of the right motor cortex, responsible for left side-body movement, was intercepted by a brain region called the precuneus. The precuneus is a section of the brain committed in part to personal memory and mental imagery. This indicates that the vivid and figurative language used by the hypnotist was experienced as real by the precuneus. This part of the brain then relayed the impossibility of the task to the motor cortex. Cojan said, "It's as if the motor cortex is connected to the idea that it cannot move (the hand) and so ... it doesn't send the message to move."
One study (Rainville, Hofbauer, Bushnell, Duncan and Price, 2002) gave 10 participants positron emission tomography (PET) scans before and after being hypnotized (see link in References). The study showed that a hypnotized brain suspends conscious functions by augmenting blood flow into the occipital region, while simultaneously lessening cortical arousal. This causes an "opening" of the mind, a bypass of the critical factor that allows suggestions to enter freely without being analyzed against ones predispositions.
Dr. Yadin Dudai co-authored a study in 2008 that showed marked changes in the prefrontal, occipital and temporal areas of the brain in participants while hypnotized. This demonstrates why trance is commonly associated with a feeling of deep relaxation.
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