An historical review

Far from being an exhaustive collection, with this short review we just want to give an idea of the articles in which the authors tried to explain what happens when our brain receives a suggestion or reacts to the influence of the context. We will conclude by citing some among the most interesting works that identified the neural correlates of hypnosis.
Forer BR (1949). The fallacy of personal validation: a classroom demonstration of gullibility. Journal of Abnormal and Social Psychology. 44, 118-123.
In this study, Bertram R. Forer, for the first time demonstrated the role of expectations when one’s own personal image is involved. After having worked during World War II as a psychologist, in 1948 he conceived an experiment based on horoscope predictions. He administered to different university students several questions about their personality (about their vision of themselves and of their character). He then gave them the test results after having added a little “trick”: all results were the same and were taken by the same page: a newspaper’s horoscope. Students were then asked to score this description of their character (again, the description was the same for everyone and was a complete invention): 0 meant a poor description while 5 meant a perfect description. The average score was 4.26. This result demonstrated for the first time that people tend to identify themselves with a judgment on them when they believe that such judgment is written specifically for them; furthermore they will try to make it precise and accurate in their mind in order to tailor it on their personality!
The “Forer effect” is well known in psychology and has been confirmed several times in different experiments. It is also known as the “Barnum effect” (from P.T. Barnum, a famous entrepreneur and circus owner).
Beecher HK (1955). The Powerful Placebo. Journal of the American Medical Association. 159, 17.
The article by Henry Beecher, 1955, is still one of the most cited when dealing with the placebo effect. With Placebo effect we refer to every effect that is ascribable to a pharmaceutical or to a procedure that is not generated by its active principles or specific properties: in this class also the language used by those who administers the substance and the administration environment are included. Normally the term is also used to define some pharmaceuticals without active principles - that is, placebos - used to control the effect of a specific pharmaceutical product. Therefore, when speaking about placebo effects we refer to a wider concept compared to what is usually imagined.
Beecher, for the first time, succeeded in demonstrating (by taking into account about 15 clinical trials of different pathologies) that more than 30% of patients, in the clinic, benefited of effects that were not caused by their therapy but, instead, by the “simple” administration of a placebo. Despite the fact that, with the passing of time, several methodological flaws were highlighted in Beecher’s research, the latter has the undoubted merit of having shifted the attention of clinicians on the importance of the context in which therapies are carried out. A phrase of Beecher is particularly enlightening: “… we don’t have to suppose that the placebo effect is only limited to ‘psychological’ responses. Many responses may be due to ‘physiological’ changes, objective changes…”.
Schachter S & Singer J (1962). Cognitive, Social, and Physiological Determinants of Emotional State. Review, 69, 379–399.
Stanley Schachter and Jerome Singer produced an experiment that described the importance of the cognitive meaning that is attributed to a situation and showed that this “perspective” could be changed with the use of words and context.
In their study 187 participants were initially subdivided into 2 groups: a control group and an experimental group. The two groups were informed that they would have to try a new drug: Suproxin (it was a fake drug). The first group, the control one, received a placebo, that is a substance that didn’t have any active principles while the second one, the experimental one, received a small dose of adrenaline and was subdivided into three other groups based on the information they received. The experimental group knew that Suproxin (that was composed by adrenaline) would have altered heart rate and would have lead to hyperventilation and tremors. Experimenters told the second experimental group, called “uninformed”, that the drug had no effect. Lastly, experimenters told to participants of the last experimental group, which was incorrectly informed, to expect some improbable symptoms caused by Suproxin (itch and headache among the others). Schacthter and Singer formulated the hypothesis that the participants of last two groups (the uninformed and the incorrectly informed one), not having sufficient information about the drug, would have looked in the surrounding context for the reasons to explain their bodily sensations (we repeat that this two groups were part of the experimental sample and thus received an adrenaline dose).
At this point, the last touch of class of the researchers consisted in adding, in the room where the subjects of the study were filling a questionnaire, an accomplice who showed exaggerated expressions of anger or happiness. Results were clear: the subjects of the two groups who were incorrectly informed about the Suproxin and the subjects who weren’t informed at all, tended to follow the mood of the accomplice. When he got angry they also felt aggressive and indignant while when the accomplice showed levity they felt euphoric. On the contrary, subjects in the correctly informed group, knowing that their sensations (palpitations, sweating etc…) were produced by the Suproxin/adrenaline, adequately explained their physiological state attributing it to the drug and tended not to imitate the emotional states of the accomplice.
Craiselneck HB, McCranie EJ & Jenkins MT (1956). Special indications for hypnosis as a method anaesthesia. Journal of the American Medical Association. 162, 1606-1608.
The first evidences about the neurophysiological substrate of hypnosis were obtained through the registration of brain waves using the electroencephalogram (EEG) or by applying electro-physiological techniques before surgical interventions. The limbic system has been one of the most deeply examined areas. It is composed by cortical and subcortical areas (hippocampus and amygdala among the rest) that are involved in emotion processing.
In this work, conducted in 1956  by Craiselneck and collaborators, we find one of the first reports: the authors, working with epileptic patients in before surgical interventions, were able to interrupt the altered state of relaxation due to a hypnotic induction by electrically stimulating the hippocampus, located in the temporal lobe. This structure, along with the amygdala, seems to be crucial in shifting attention and in reacting to emotionally relevant stimuli: in fact, it is well known that the amygdala mainly regulates the orientation toward new stimuli while the hippocampus acts on habits and repetitive stimuli. As a matter of fact, as it can be learned from literature, both processes are fundamental in hypnosis: in fact one of the aims of the hypnotic states is to manage irrelevant elements and to shift the focus of attention towards other stimuli which represent the main source of information.
While providing a description of one of the main “in vivo” brain research methods, this article pointed at some definite cerebral areas involved in hypnotic suggestions.
De Pascalis V (1999). Psychophysioligical correlates of hypnosis and hypnotic susceptibility. International Journal of Clinical and Experimental Hypnosis. 47 (2), 117-143.
In the field of psychophysiological studies a distinction between subjects with high suggestibility and subjects with low suggestibility - that is between subjects able to better respond to hypnotic suggestions and subjects whose response is less evident - was hypothesized.
De Pascalis, in this framework, explored the so called “gamma band”. The gamma band is a group of waves that oscillates between 25 and 100 Hz (mean: 40 Hz) that is supposedly involved in the processes of focusing conscious attention (focused arousal) and generally in the unification of different conscious perceptions (it manifests itself as an activity diffused to the whole cerebral cortex). Using a recall paradigm involving emotional experiences, the author demonstrated that in subjects with high suggestibility, during the recall of happy experiences, a rising in gamma waves in the posterior regions of both lobes can be observed, while for angry or fearful recalled experiences, a rising of electric signal density can be observed in the right hemisphere in correspondence with a reduction of density in left posterior areas. These differences were not observed in subjects with low susceptibility, while in highly suggestible subjects the differences in electrical signal became significantly higher during hypnotic state compared to recalls in neutral situations. In a recent article, the same author administered painful (electric) stimuli to subjects with high, medium and low hypnotic susceptibility, demonstrating that the first ones, when under hypnosis, obtained a bigger reduction of pain and perceived stress than subjects with medium and low susceptibility: this analgesic perception is closely related to the reduction of gamma waves in frontal areas (De Pascalis et al., 2004).
Mészáros I & Szabó C (1999). Correlation of EEG asymmetry and hypnotic sysceptibility.  Acta physiologica Academiae Scientiarum Hungaricae, 86(3-4), 259-263.
Several researches have explored the connection between brain lateralization and hypnotic states, showing initially a strong correlation between a higher activation of the right hemisphere and hypnotic susceptibility.
This article is about this line of research and also demonstrates for the first time (at a cerebral level) the differences between different styles of hypnotic inductions. Mészáros and Szabó, in their research, focused on hypnotic susceptibility showing that the right temporal-parietal region of highly suggestible subjects has a greater electric response (calculated as mean of the recorded signal) compared to the left cortex, while subjects with low suggestibility show a left predominance or a balance in all derivations (areas used to record the electric signal) between the hemispheres. By using an indirect hypnotic induction (an Ericksonian induction) the same right preponderance of electric signal can be recorded in subjects with low suggestibility, proving the fundamental importance of the parietal-temporal associative area in hypnotic induction while, at the same time, demonstrating a substantial difference between classical and indirect inductions.
Maquet P, Faymonville ME, Degueldre C, Delfiore G, Franck G, Luxen A, Lamy M (1999). Functional neuroanatomy of hypnotic state. Biological Psychiatry, 45, 327-333.
The most recent studies on neuroanatomical correlates of hypnosis derive from modern brain imaging techniques measuring blood flow: thanks to this technique the level of activity of brain areas during a specific task can be visualized.
In this work by Maquet, one of the first studies carried out with PET (Positron Emission Tomography), a hypnotic induction based on the recall of autobiographical material was used in order to identify which areas were more active during the hypnotic state. As control situation a recall of autobiographical memories that wasn’t induced with hypnotic suggestions was used. As already showed by previous studies, the simple recall of autobiographical memories, without a hypnotic induction, activated temporal and middle temporal areas involved in the re-elaboration of past episodes. Differently from control situation, during the hypnotic state, a very wide activation, that involved occipital, parietal, pre-central and prefrontal areas, along with the cingulate cortex, was observed. Furthermore, the regions activated during hypnosis were different than those activated in the control situation. Results allowed to demonstrate that after the hypnotic induction, what happens is not just a recall of mnestic material: an involvement of sensory and motor areas can be observed, just as it happens during normal perception and motor actions, and this activation occurs in the absence of external inputs (visual or tactile stimuli for instance) or outputs (executed movements). As proposed by the authors, perceptive elaboration without input in parietal-occipital areas, during hypnosis, is similar to the processes of imagination. For instance, the activation of frontal areas confirms the similarity with motor imagery tasks in which areas that are considered as motor nodes activate because of the simple imagination of movement without its true execution. Cingulate cortex is instead a structure involved in attention shift processes, and its activation can be well connected with the interpretation of hypnosis as an instrument that allows to focus the subject on a particularly relevant event.
Derbyshire SWG, Whalley MG, Oakley DA (2009). Fibromyalgia pain and its modulation by hypnotic and non-hypnotic suggestion: An fMRI analysis. European Journal of Pain. 13, 542 – 550.
 In this recent experiment it was showed that it is possible to modulate pain through hypnosis in patients affected with fibromyalgia (a condition that manifests itself with symptoms such as rigidity and chronic muscular pain). The neural correlates of this modulation were studied using functional magnetic resonance (fMRI). Analgesic suggestions were given both during a hypnotic induction and out of it: results showed that in both conditions patients achieved a greater control over pain, but only during hypnosis a significant reduction of painful sensations was reported. Magnetic resonance showed cerebral activation of several areas such as the mid-brain, cerebellum, thalamus, cingulate cortex and also of the primary and secondary sensory cortices, along with insular, parietal and prefrontal cortices. Activations, even if present in both conditions, were higher for analgesic suggestions administered during the induction of the hypnotic state, mostly in the anterior cingulate cortex, in the anterior and posterior insula, cerebellum and inferior parietal cortex. In literature, these areas are closely connected to a specific cerebral network called “pain matrix”, which is crucial for the elaboration of noxious stimuli in human beings.
The articles we collected are just some of the stones with which the intricate path that connects suggestion (verbal ones but also those related to environmental expectations) and the brain was built. Obviously the road is still evolving both in the field of hypnosis and in what concerns brain circuit research. We can however already state, thanks to these works, that the mind can be considered as “incarnate”, that is intrinsically bond to the body and to its sensations. Using hypnosis (but also acting in a specific setting) means putting ourselves in relation with the nervous system of the interlocutor and listening to the answers that the latter provides.