After hypnosis, subjects often report not having perceived irritating noises. This can be explained by a restriction of attention, which has been studied experimentally for instance by Grond et al. (1995) 1). An examination of the regional glucose metabolism in the brains of high-suggestible hypnotized test subjects by positron emission tomography indicated a reduction of ‘preparedness’ for stimulus processing in the primary visual and auditory centres of the brain. In addition to the restriction of attention subjects under hypnosis also report about spontaneous changes in bodily perceptions i.e. changes that had not been suggested to them. During prolonged hypnosis it is possible, that legs or arms are perceived as being longer or shorter than usual or that other parts of the body seem to change, e.g. lips to enlarge or that the head appears to be bigger than normal. Illusory movements are also possible as evidenced by the report of patients about a turning of the body or on the sensation of slipping from the couch. Sometimes patients have the impression that certain parts of the body, e.g. legs or arms, no longer exist. Additionally, spontaneous feelings may occur of heaviness or of agreeable lightness accompanied by the sensation of muscle relaxation, that can be objectified by means of the electromyogram 2).
“Trance logic” is regarded as a further distinguishing feature of hypnosis. “Trance logic” represents the tolerance towards logic inconsistencies under hypnosis: During a hypnotic return into childhood (hypnotic age regression) it is possible, that subjects who during their childhood had not yet mastered the language of the experimenter (e.g. German) answer correctly the questions they are asked using the language of their childhood (e.g. Portuguese) 3). But doing this is “illogical” since at that time the questions would have been unintelligible to the subjects.
After hypnosis, subjects are often astonished at the vividness of the imaginations that were suggested to them. High-susceptible subjects to whom the experience of a scene of their school-days was suggested, sometimes report the experience of according imaginations using the words: “it has been like I would have been there”. Such reports resulted in the assumption that the improved visual imagagery is a defining characteristic of the hypnotic state 4).
Distorted time perception represents a further feature of hypnotic experience. Clinical studies as well as experiments indicate that patients and subjects often markedly underestimate the time they had been under hypnosis 5) ; according to our experience, these underestimations may come to about 80 percent which means that a hypnotic session of one hours` duration is estimated by the test subjects to have taken only 10 minutes. Under hypnosis time intervals are also underestimated significantly in comparison with relaxation control groups 6).
In addition to increased suggestibility and an easier access to emotions, trance is also regarded as a state that facilitates dissociative processes. Dissociation can refer to cutting off external stimuli which for instance is the case with hypnotic analgesia in which intense external stimuli caused by surgical operations, as for example Caesarean section, appendix operation etc. 7), teeth extraction 8), dental implant 9) or even gall bladder operation, do not lead to the experience of pain 10). But hypnotic dissociation may also refer to ‘splitting off’ contents from consciousness as in the case of posthypnotic amnesia when normally available information - after the suggestion to forget it - is no longer remembered.
If asked to describe the hypnotic state a person who is able to experience hypnosis may answer that it would be like just before falling asleep. The hypnotic state is experienced like being between awake and asleep when thinking is replaced by imaginations that have emotional overtones that arise spontaneously and that are not logically arranged. It is because of this form of vivid spontaneous, not rational thinking under hypnosis that hypnosis is also called a primary process-like state by researchers of hypnosis 11).
Physiological changes in the brain: While concluding empirical evidence is still due for the popular assumption since the 1970s that hypnosis is associated with an increase in activity of the right hemisphere 12), studies have been published that indicate that event related potentials (ERP`s) are influenced by hypnotic changes of perceptive and imaginative processes 13). Nowadays, modern brain imaging techniques are used for the investigation of hypnosis. Here physiological activity of the brain depends on the given contents of trance: It has been shown in PET-studies that under hypnotically suggested calmness the regional bloodflow increases in the frontal cortex, especially in the left hemisphere 14).
Changes in autonomous functioning: The relaxation experienced under hypnosis is accompanied by a dampening of the sympathetic level of arousal and thus results in a reduction of those bodily functions that are controlled by the autonomous nervous system. These include the reduction of breathing rate, the deceleration of the heartbeat, the reduction of systolic blood pressure, changes in body temperature, a reduction of spontaneous electrodermal activity as well as a drop in muscle activity as measured by electromyogram 15).
Up to now, endocrinological parameters have rarely been considered in investigations concerning hypnosis. The influence of hypnosis on autonomous functioning like heartbeat leads to the assumption that the dampening of the sympathetic nervous system under hypnosis takes place by means of a reduction in catecholamines. We performed a hypnosis experiment, including a stress (mental arithmetics) and a control condition (quiet sitting), monitoring the plasma levels of adrenalin and noradrenalin each time before, during and 90 minutes after carrying out a condition.
A clear drop in plasma adrenalin and plasma noradrenalin became apparent during the hypnosis condition in contrast to stress that led to a rise in the level of catecholamines whereas the control condition did not show significant differences over time 16).
Blood count: There is a change in blood count after hypnosis. A reduction occurs in the number of leucocytes by about 20 percent after hypnosis 16), which is controlled, as mentioned before, by a reduction in the level of catecholamines that induces the leucocytes to adhere to the vascular endothel 16). Due to the increased adhesion of leucocytes to the vascular walls there are less leucocytes in circulation and therefore also less leucocytes in the (venous and capillary) blood test. About two hours after hypnosis we observed a postponement of differential blood count, i.e. a rise in lymphocytes and a reduction of neutrophiles 16) 17).
Clinical results: Evidence for long-term influences of hypnosis on physiological processes can be found in clinical studies. Training in hypnosis induces a significant reduction in blood pressure that still continues six months after completing the training, and that is superior to biofeedback training 18). A distinct reduction of warts is reported after hypnotic treatment in comparison with a placebo and a control group 19). After hypnotic treatment of haemophilia a significant reduction can be observed in the medicaments needed compared to normal provision of medical care 20). Patients with duodenal ulcers, who did not respond to conventional treatment, showed a clear improvement after hypnotic treatment in comparison with a control group, that were given only medication 21). Even with asthma patients hypnotic treatment produced significant improvement compared to various control groups 22).