Hypnosis is an altered state of consciousness that may resemble sleep but which is artificially induced. Most often, hypnosis occurs during hypnotherapy, in which a hypnotist will use suggestion to help a patient to explore repressed memories, thoughts, and ideas. Some people also practice self-hypnosis. Despite that fact that a person experiencing hypnosis appears is relaxed and may experience a mental state similar to sleep, the brain during hypnosis is as active as if the individual were fully awake.
Researchers have found that during hypnosis the brain is capable of attention that is deeply focused. Random or spontaneous thoughts are less likely to occur to a person who is undergoing hypnotherapy. Likewise, the brain is more susceptible to suggestion. This means that an individual undergoing hypnosis is more likely to follow orders from the person performing hypnosis and is likely after the procedure to be influenced by ideas and behaviors that were discussed while he or she was hypnotized.
A theory regarding what happens to the brain during hypnosis regards communication among the brain's cognitive systems. The cognitive systems are those which allow people to process information, categorize information, and create associations. Researchers who believe that communication among the brain's cognitive systems are disturbed point to a number of mental effects of hypnosis as evidence. For example, many undergoing hypnosis report a sense of detachment and a reduction in spontaneous thought.
There is much debate concerning which physical or neurological effects occur in the brain during hypnosis. Some specialists believe that the frontal lobes play a significant role in creating this altered state of consciousness. The frontal lobes are the part of the brain responsible for organizing intentional action. Since hypnosis requires an individual to participate in involuntary action, many specialists theorize that the functions of the frontal lobes are weakened or altered in some other way.
While there is no conclusive evidence that there are any neurological changes that occur in the brain during hypnosis, many theorists have proposed various ideas that are used to describe the hypnotic procedure. One popular theory is information theory. This idea states that the hypnotist is able to hypnotize an individual by increasing the signal-to-noise ratio. In other words, the hypnotist reduces the presence of distracting thoughts, sounds, and objects in order to make suggestive messages more easily received.
Another popular theory to describe the brain during hypnosis is systems theory. This idea is based on the activity of the nervous systems of the individual undergoing hypnosis. The hypnotist, according to this theory, decreases or increases the activity of various subsystems within the patient's nervous system.