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Hypnosis and the Brain: Findings in Neurological Research

By: Judith E. Pearson, Ph.D.

The human brain is the most complex organization of matter in the known universe. Containing over 100 billion neurons richly interconnecting with between 1,000 and 100,000 others, the brain forms an infinitely complex non-linear, dynamic system. The potential number of emergent states and behaviors is virtually limitless and brain's vast neuronal system with its electro-physiological activity never resides in exactly the same state twice. (Furman, 1996)

Although the American Medical Association approved hypnosis as a clinical tool in 1958, the way in which hypnosis affects the brain and the neurological system remains somewhat of a mystery. The exact neurological phenomena of hypnosis are seldom taught in hypnotherapy practitioner training. Some practitioners don't concern themselves with the question of neurological factors, and others simply assume that hypnosis is a state of relaxation in which brain activity slows down. To expand their knowledge, practitioners would do well to ask questions such as: "What happens to the brain, under hypnosis?" or "How does trance differ, neurologically, from normal waking consciousness?" or "What neurological factors are involved in hypnotizability?"

Over the past two decades, scientists have begun to investigate these questions, with the aid of brain scan technology such as Positron Emission Tomography (PET), Electro-Encephalograms (EEGs), and Magnetic Resonance Imaging (MRI). Studies using these instruments show that, during hypnosis, brain activity does change. The authors of these studies interpret their observations of brain activity to offer hypotheses about common hypnotic phenomena such as enhanced suggestibility, pain reduction, amnesia, time distortion, and hallucination.

Despite two decades of research, there are few consistent findings. These inconsistencies may be due to the parts of the brain under observation; the type of induction used for hypnosis; the instructions given while the subjects are in trance; the requirements of the task to be performed by the subjects while in trance, and the type of instruments used to acquire the observations and measurements. To further complicate matters, many studies report differences in findings between highly hypnotizable subjects and those with low hypnotizability. Thus, hypnotizability seems to be a factor in determining how anyone might respond to hypnosis, at the neurological level.

This paper will attempt to clarify and summarize what research shows and what the experts say about the brain under the influence of hypnosis. First, this paper debunks the commonly held assertion that hypnosis relaxes the brain. Next, it summarizes a sampling of research findings conducted over the past decade that concerns hypnosis and neurology. The final section will discuss conclusions that hypnotherapy practitioners might draw from neurological research.

Hypnosis is Not Relaxation of the Brain

Scan the Internet using the search words "hypnosis" and "brain," and you'll find web sites explaining that hypnosis as a state of relaxation in which brain activity slows down. Relaxation does show up on EEG readings as a slowing of oscillations in the electrical activity of the brain. This electrical activity is characterized as "cycles per second," or hertz (Hz). The range of 30 to 40 Hz is the Gamma range, indicating heightened alertness. The range of 13 to 30 Hz is the Beta range, usually associated with normal waking consciousness. The range of 8 to 12 Hz is the Alpha range, associated with light relaxation. The range of 4 to 7 Hz is the Theta range of deep relaxation. The range at 3 Hz or lower is the Delta range and it is associated with sleep. In fact the state that occurs just before sleep when people are just beginning to doze is aptly named "the hypnogogia." Trance is often said to occur in the Alpha and Theta range, and it probably does, when the hypnotic method involves repeated instructions to "relax deeply."

Using EEG levels that indicate degrees of relaxation, as a definition of trance is problematic in that, while a person is relaxing, the brain may exhibit these changes in the absence of any hypnotic instructions. In fact, according to Jamieson (2007), the hallmarks of hypnosis are absorption, dissociation, and suggestibility, and not relaxation.

To say that relaxation is the brain's response to hypnosis is overly simplistic. Scientists have found many changes in the brain during hypnosis that do not fit the pattern of relaxation. Studies of the brain during hypnosis produce widely varying findings, indicating that, in trance, some parts of the brain show more activity and some parts show less activity. Some parts of the brain appear to interact under hypnosis, while some parts do not, when, under non-hypnotic circumstances, they would be expected to interact. Now let's turn to those studies.

A Sampling of Research Findings

Studies conducted with neurological measurements show that subjects in trance demonstrate differences in brain activity as compared with non-trance circumstances. The findings are more often observed with highly hypnotizable subjects, as compared with subjects having low hypnotizability. The studies summarized below show that hypnosis is associated with changes in the activity of the Anterior Cingulate Cortex (ACC), changes in brain connectivity, hemispheric shifts, and variations in brain oscillations. A final subsection addresses possible neurological differences in hypnotizability. The findings show that hypnosis can affect the brain in many ways, at various locations throughout the brain structure.

Changes in Anterior Cingulate Cortex Activity

The part of the brain most often reported to show changes in activity under hypnosis is the ACC, located just behind the frontal lobes. This is the part of the brain that performs executive functions. It can shift attention from one task to another, mediate between two competing perceptions, provide selective attention, and promote cooperation. Changes in the ACC seem to be a neurological component of hypnotic trance. In fact, Jamieson and Woody (2007) have stated that: "Increases in the activation of various regions of the ACC have been a common denominator in almost all imaging studies of the effect of hypnosis or various specific hypnotic suggestions." (p. 123)

Rainville et al (1999), for example, investigated brain activity before and after hypnosis through PET scans of ten volunteer subjects. The subjects rated their perceived levels of "mental relaxation" and "mental absorption." The researchers found differences in the blood flow to the ACC, the thalamus, and the brainstem, pre- and post-hypnosis. In the hypnotic state, PET scans showed a "decrease in cortical arousal" (a calming effect) and a reduction in cross-modality suppression (less inhibition) for subjects who reported mental relaxation. For subjects who reported mental absorption, PET scans showed an increase in blood flow to the brain's "attentional system." In a similar study, Rainville and Price (2003) found that subjects who reported relaxation during hypnosis had reduced cerebral blood flow in the ACC, the brain stem and the thalamus. However, subjects who reported absorption during hypnosis demonstrated increased activity in these areas.

Gruzelier (Future Pundit, 2004) compared 12 subjects who were receptive to hypnosis and 12 who were resistant to hypnosis. Gruzelier observed subjects' brain activity with Functional MRI while they completed the Stroop Test under hypnosis. The Stroop Test is a standard psychological test that probes cognitive conflict. The test shows words that are the names of common colors, such as blue, green, or red. Subjects must name the color of each word. However, the words are printed in another color of ink. For example, the word "blue" could be printed in red or yellow ink. People usually take longer to name a color when the color name is printed in mismatched ink, because the brain must first resolve the conflict. The subjects were told to see the words as gibberish and name the color only. Subjects who were receptive to hypnosis performed better on the test and had more activity in two parts of the brain: 1) the anterior cingulated gyrus, the area of the brain that can respond to errors and evaluate emotional outcomes and 2) the left side of the prefrontal cortex, the part of the brain responsible for cognitive processing and behavior.

In a similar study, and one of many such investigations, Raz et al (2005) illustrated that hypnosis could reduce cognitive conflict in highly hypnotizable individuals. The researchers used Functional MRI and readings from scalp electrodes to monitor brain activity while 16 subjects completed the Stroop Test, after hypnosis. The imaging data indicated that hypnotizable subjects showed reduced brain activity in both visual areas and the ACC, which is involved in conflict monitoring. The researchers concluded that "[hypnotic] suggestion affects cognitive control by modulating [brain] activity." Such findings could mean that, at least for people who are highly hypnotizable, hypnotic trance can temporarily change brain activity to enhance the ability to accept suggestions without resistance or internal conflict.

Egner et al (2005) used EEG measurements to find that, in highly hypnotizable subjects, there was a reduced connection between the lateral frontal cortex (area of cognitive control) and the ACC, both of which control response monitoring. The conclusion was that highly hypnotizable subjects are more likely, under hypnosis, to accept suggestions, without feeling a need to resist or evaluate the suggestions.

Commenting on proposed interpretations by Raz et al, and on similar ones put forth by Egner et al (2005), Jamieson (2007) wrote that, "Flexible adaptation in cognitive control is impaired in hypnosis but... this very condition may be the key to enabling the hypnotized person to implement the specific suggestions, when made by the hypnotist, without interference from higher order monitoring systems." (p. 2-3)

Changes in Connectivity

Some studies have shown that hypnosis affects the connectivity of various areas of the brain that register pain (Boly et al, 2007). In a study on hypnosis and pain response, Maquet et al (1999) compared pain responses for subjects told to remember pleasant memories, both in and out of hypnotic trance. The researchers found that hypnosis modulated connectivity between the mid cingulated cortex, the thalamus, and the prefrontal brain, affecting areas responsible for cognitive appraisal and perception of pain. They also found that under the hypnotic condition, activity was more widely distributed across the entire brain. In another study, Miltner and Weiss (2000) found that under hypnosis, a "breakdown" in connectivity between the limbic brain and the frontal cortical regions of the brain reduced the perception of pain.

A Shift to the Right Brain

Other studies have found that hypnosis shifts brain activity to the right brain, reduces activity in the left brain, and causes "inhibition" in the frontal lobe (DePascalis, 2007). In a single-subject case study, Alexander et al (2007) conducted EEG measurements on a highly hypnotizable individual during hypnosis and again, months later, when the subject was not hypnotized. Under hypnosis there was a significant increase in brain frequency patterns overall and a shift to more activity in the right frontal lobe. The researchers interpreted this observation to mean that the subject had a "heightened state of attention" while in hypnotic trance.

Changes in Brain Oscillations

Ray (2007) has written that there is "a solid relationship between electro-cortical activity, hypnosis and hypnotizability...EEG theta activity and the cingulated cortex are two important physiological mechanisms which are active during the hypnotic experience." (p. 223) While EEG measurements do show variations in brain oscillations under hypnosis, the meaning of such observations is uncertain.

Graffin et al (1995), for instance, found that hypnotizable subjects had greater theta activity in the frontal cortex, as compared to less hypnotizable subjects, prior to hypnosis. However no such differences were apparent during hypnosis and, in fact, for both groups, theta levels increased in the posterior areas of the cortex, and alpha levels increased over all the areas measured. Graffin's team wrote that, "Because our understanding of EEG theta activity is limited, it is difficult to state clearly whether the increase in theta activity seen during the actual hypnotic induction was related to depth of hypnotic trance or the accompanying relaxation and absorption, or was more related to the process of cognitively focusing on the instructions verbally presented." (p. 128)

Commenting on such studies, Lynn et al (2007) remarked that, "The fact that responses to hypnotic suggestions are associated or correlated with EEG asymmetries or increased theta...does not warrant the conclusion that hypnosis causes the EEG patterns." (p. 152) In further opinion on the observation of neural effects under hypnosis, these authors have stated that "It is not clear that the experience and neural correlates of trance would be the same for all hypnotic subjects or even all virtuosos. Having different preconceptions about trance might lead to different subjective states and therefore to different neural substrates." (p. 157) In a similar vein, Burgess (2007) wrote that, "despite two decades of research, no EEG marker of hypnosis has been found. Claims have been made for alpha, theta and gamma oscillations, but none show the specificity required... (i.e., to distinguish hypnosis as a state separate from other states, such as waking consciousness or sleep)." (p. 203)

Differences between High Hypnotizables and Low Hypnotizables

There is some evidence that hypnosis seems to affect the brains of highly hypnotizable subjects more than it affects the brains of subjects having low hypnotizability, and that the brains of highly hypnotizable people may be inherently different from those who are less so. In research studies, hypnotizability is usually measured by the Harvard Group Scale of Hypnotic Susceptibility: A (Shor and Orne, 1962) and/or the Stanford Hypnotic Susceptibility Scale: Form C (Weitzenhoffer and Hilgard, 1962), which record observations of subjects' behavior in response to suggestions that are usually associated with hypnotic trance (i.e., hand levitation).

Rawlings (1977) studied hypnotizability in identical twins and found a strong genetic component. Numerous studies have demonstrated that highly hypnotizable subjects have a more effective frontal attentional control system than subjects with low hypnotizability (Crawford and Gruzelier, 1992; Crawford, 1994; Gruzelier, 1999), suggesting that hypnotizable individuals have structural differences in the "wiring" of their brains. Horton et al (2004) used MRI measurements to show that the anterior corpus callosum (the main fiber tract connecting the cerebral hemispheres) is larger in individuals who test as highly hypnotizable. Their theory is that this thicker corpus callosum allows greater "gating" to screen out pain and direct attention away from unwanted stimuli. Thus, highly hypnotizable individuals have success in using hypnosis to reduce pain. The thicker corpus callosum might be another "biomarker" for hypnotizability, along with eye roll capacity as noted by Spiegel (1972).

If hypnotizability is a function of neurological characteristics (versus processes), such a conclusion would, of course, pose additional and highly intriguing questions. If hypnotizability is a function of innate characteristics, how then do we account for findings that hypnotizability can be enhanced with training (Bonnington et al, 2006)? Can those with low hypnotizability improve their susceptibility with practice and thereby develop the areas of the brain that facilitate the trance experience? Does hypnotizability improve or diminish with the passage of time, as with other innate abilities? Do differences in hypnotizability have any bearing on the fact that approximately 35% of research subjects respond to placebos (Rossi, 1986)? Perhaps future research will provide the answers to these questions.

Final Remarks

Can hypnotherapy practitioners draw any conclusions from studies of the brain and hypnosis? Can we say with certainty how hypnosis affects the brain? The answers to these questions do not come easily. Scientists have observed that changes occur in the brain during hypnosis, but what those changes tell us, from a practical perspective, is not clear.

Gruzelier (2000) has written that, "Hypnosis is an altered state of brain function organization" and that "brain activation in a number of regions can be observed during hypnosis..." (p. 51). Jamieson and Woody (2007) have added that "...disruptions in the process of cognitive control play a central role in the generation of hypnotic phenomena and...these disruptions stem from a fundamental shift in the organization of executive functions within the brain." (p. 119) This factor seems to make hypnotic subjects more likely to accept suggestions. Coming from another point of view, however, Burgess (2007) has stated that it is difficult to assign a psychological interpretation to a physiological result and that the functions are of the brain not well understood.

Although hypnosis does appear to modify brain processes, hypnosis does not create a unique brain signature. Burgess (2007) has written that no one neurological finding can be attributed to hypnosis alone, because such findings can also appear in non-hypnotic circumstances. He has written that hypnosis does not represent a unique pattern, and that hypnosis is not distinguishable from sleep or from waking consciousness. There seems to be no distinct neurological pattern that defines hypnosis and only hypnosis. Moreover, it seems likely that we could observe brain patterns that are similar to those found under hypnosis, for other mind-body therapies that are sometimes used alone or in conjunction with hypnotherapy, such as guided imagery, progressive relaxation, and mindfulness meditation. Lazar et al (2000), for example, using functional MRI, observed that subjects performing relaxation and meditation had increased neural responses for those areas of the brain involved in attention and control of the autonomic nervous system.

Studies of hypnosis and the brain show inconsistent findings. One problem seems to be that researchers do not agree on a single definition of hypnosis. At this point, there is a debate in the scientific literature as to whether trance is an altered state of consciousness separate from waking consciousness and sleep, or a trait that some people exhibit in response to psycho-social demands (Lynn, et al, 2007). Another problem in interpreting research findings is that researchers do not use one standardized method of trance induction in all studies and the method of hypnosis is rarely explained in the literature. Because there are so many different ways to induce trance, it is possible that the brain effects observed are a function of the type of induction employed, and the task which the subjects are asked to perform during hypnosis. Lynn et al, in fact, have commented that, "There is a surprising degree of consensus, among researchers...that hypnosis is not a uniform state, but rather reflects what participants 'do' during hypnosis...which varies as a function of the suggestions they receive." (p. 147)

Ray (2007) has speculated that the social aspects of the hypnotic experience promote receptivity to control by the person giving suggestions. He has hypothesized that hypnosis evokes, in some individuals, an alteration in feeling that deactivates the higher order processes (i.e., critical thinking) of the neo-cortex and switches thinking over to the limbic system and thus "feeling states become altered to agree with the intent of the hypnotists suggestions." (p. 250) Perhaps trance is just another name for compliance.

Practitioners can note that studies on neurology do not address what parts of the brain or what brain processes might constitute the "unconscious mind." This term "unconscious mind" is a construct, referring to cognitive processes that often seem outside of conscious awareness and/or conscious control. Rossi (1986) has put forth that the unconscious mind can best be characterized as the limbic system, the primitive brain comprised of the hippocampus, hypothalamus, the pituitary gland, amygdala and the brain stem. This part of the brain regulates emotions and biological drives (appetite, sex, sleep, and motivation) and emits neuro-transmitters that activate the endocrine system, influence the immune system, and regulate the autonomic nervous system.

Practitioners can conclude from this review that; 1) hypnosis does affect the brain in various ways to promote suggestibility, 2) hypnosis may increase activity in some parts of the brain and decrease activity in other parts, 3) hypnosis seems to influence connectivity in some parts of the brain, 4) individuals vary in terms of hypnotizability and in their response to hypnosis, 5) what happens neurologically under hypnosis is dependent on the hypnotic methods employed and the instructions given. While these conclusions may not seem highly dramatic, they seem to be all that we confidently state at this point in time. By following the research on neurology and hypnosis, hypnotherapy practitioners can avoid the mistake of making overly simplistic claims about hypnosis and the brain and can better appreciate the complexity of the minds they seek to influence and guide.


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Sources: Daniel Amen (1998) Change Your Brain and Change Your Life. New York: Three Rivers Press and Mark B. Weisberg, (2007) The Power of Mind/Body Medicine. A workshop by the National Institute for the Clinical Application of Behavioral Medicine, Mansfield Center, CT.

Judith E. Pearson, Ph.D. is a licensed psychotherapist, hypnotherapist and practitioner of Neuro-Linguistic Programming, practicing in Springfield, Virginia.

She has written The Weight, Hypnotherapy and You Weight Reduction Program: An NLP and Hypnotherapy Practitioners' Manual (Crown House Ltd.).


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