In order for a hypnotherapist to convey positive suggestions for change, the patient must be in a receptive state. The state is called trance and the method of achieving a trance is through induction. Induction techniques are many and varied and involve the therapist offering suggestions that the patient follows. The formerly common "your eyes are getting heavy" suggestion may still exist, but other more reliable and acceptable (by the patient) forms of induction have come to the forefront. The artful hypnotherapist is always aware of the present condition of the patient and uses this information to lead him/her down the path of induction. In its lighter stages, trance can be noted by the relaxation of muscles. At this point, hands can levitate when given the suggestion, and paresthesia, a feeling of numbness, can be induced. In a medium trance, a patient can be led to experience partial or complete amnesia , or failure to recall events of the induction after the fact. A deep trance opens the patient to powerful auditory, visual, or kinesthetic experiences. The phenomenon of time distortion is experienced most profoundly at this level. Patients may believe they have been away briefly, and may react with disbelief when told they were away much longer. Although some work can be done in lighter states of trance, the best circumstance for implementing change is when the patient reaches a deep trance state. At this level, the patient is focused inwardly and is more receptive to positive suggestions for change. This is also the point at which the therapist can invoke posthypnotic suggestions, or instructions given to the patient so he/she will perform some act or experience some particular sensation following awakening from the trance. For example, these suggestions, if accepted by the patient, can be formed to make foods taste bad, cigarettes taste bad, delay impulses, curb hunger, or eliminate pain. However, it should be noted that posthypnotic suggestions given to a person, which run counter to the person's value system or are not something they are likely to do under ordinary circumstances, will not be accepted and therefore not implemented.
Hypnosis, an enhanced state of inner focus, can be an effective tool for improving a range of symptoms, including those related to mood and learning. The ADHD drug methylphenidate (Concerta, Ritalin) has been shown to increase hypnotizability in a sample of patients with ADHD and thus may enable patients to benefit from adding hypnosis to their treatment regimens.
The first neuropsychological theory of hypnotic suggestion was introduced early by James Braid who adopted his friend and colleague William Carpenter's theory of the ideo-motor reflex response to account for the phenomenon of hypnotism. Carpenter had observed from close examination of everyday experience that, under certain circumstances, the mere idea of a muscular movement could be sufficient to produce a reflexive, or automatic, contraction or movement of the muscles involved, albeit in a very small degree. Braid extended Carpenter's theory to encompass the observation that a wide variety of bodily responses besides muscular movement can be thus affected, for example, the idea of sucking a lemon can automatically stimulate salivation, a secretory response. Braid, therefore, adopted the term "ideo-dynamic", meaning "by the power of an idea", to explain a broad range of "psycho-physiological" (mind–body) phenomena. Braid coined the term "mono-ideodynamic" to refer to the theory that hypnotism operates by concentrating attention on a single idea in order to amplify the ideo-dynamic reflex response. Variations of the basic ideo-motor, or ideo-dynamic, theory of suggestion have continued to exercise considerable influence over subsequent theories of hypnosis, including those of Clark L. Hull, Hans Eysenck, and Ernest Rossi. It should be noted that in Victorian psychology the word "idea" encompasses any mental representation, including mental imagery, memories, etc.
An approach loosely based on information theory uses a brain-as-computer model. In adaptive systems, feedback increases the signal-to-noise ratio, which may converge towards a steady state. Increasing the signal-to-noise ratio enables messages to be more clearly received. The hypnotist's object is to use techniques to reduce interference and increase the receptability of specific messages (suggestions).
“Each unhealthy current behavior, such as smoking, losing one’s temper, excessive alcohol consumption, or compulsive overeating has a chain of events that laid the foundation for all of our current unhealthy choices. Through the ‘memory chip’ that has been laid down in the subconscious mind, we can trace back the experiences and subconscious decisions we made as children that may be leading us to the behavior that is no longer healthy for us.”
There are numerous applications for hypnosis across multiple fields of interest, including medical/psychotherapeutic uses, military uses, self-improvement, and entertainment. The American Medical Association currently has no official stance on the medical use of hypnosis. However, a study published in 1958 by the Council on Mental Health of the American Medical Association documented the efficacy of hypnosis in clinical settings.
Not every person is hypnotizable to the same degree; some aren’t hypnotizable at all. “Hypnotizability … is modestly correlated with absorption, a personality construct reflecting a disposition to enter states of narrowed or expanded attention and a blurring of boundaries between oneself and the object of perception,” writes John F. Kihlstrom, a psychologist at the University of California, Berkeley, in a 2013 paper in Cortex. “Absorption, in turn, is related to ‘openness to experience,’ one of the ‘Big Five” dimensions of personality.”
In his later works, Braid reserved the term "hypnotism" for cases in which subjects entered a state of amnesia resembling sleep. For other cases, he spoke of a "mono-ideodynamic" principle to emphasise that the eye-fixation induction technique worked by narrowing the subject's attention to a single idea or train of thought ("monoideism"), which amplified the effect of the consequent "dominant idea" upon the subject's body by means of the ideo-dynamic principle.
In the 1950s, Milton H. Erickson developed a radically different approach to hypnotism, which has subsequently become known as "Ericksonian hypnotherapy" or "Neo-Ericksonian hypnotherapy." Erickson made use of an informal conversational approach with many clients and complex language patterns, and therapeutic strategies. This divergence from tradition led some of his colleagues, including Andre Weitzenhoffer, to dispute whether Erickson was right to label his approach "hypnosis" at all.