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.
During hypnosis, a person is said to have heightened focus and concentration. The person can concentrate intensely on a specific thought or memory, while blocking out sources of distraction. Hypnotised subjects are said to show an increased response to suggestions. Hypnosis is usually induced by a procedure known as a hypnotic induction involving a series of preliminary instructions and suggestion. The use of hypnotism for therapeutic purposes is referred to as "hypnotherapy", while its use as a form of entertainment for an audience is known as "stage hypnosis". Stage hypnosis is often performed by mentalists practicing the art form of mentalism.
After hypnosis, participants’ memories were tested twice while the fMRI scanner recorded their brain activity. For Test 1, they were asked 40 questions about the content of the movie (for example, the actress knocked on her neighbor’s door on the way home) and 20 questions about the context in which they saw the movie (for instance, during the movie, the door to the study room was closed). These questions required a “yes” or “no” response. For Test 2, participants were asked the same 60 recognition questions, but first they heard the cue to cancel PHA. So Test 1 measured memory performance and brain activity while the PHA suggestion was in effect and Test 2 measured memory performance and brain activity after it was cancelled.
But psychiatrists do understand the general characteristics of hypnosis, and they have some model of how it works. It is a trance state characterized by extreme suggestibility, relaxation and heightened imagination. It's not really like sleep, because the subject is alert the whole time. It is most often compared to daydreaming, or the feeling of "losing yourself" in a book or movie. You are fully conscious, but you tune out most of the stimuli around you. You focus intently on the subject at hand, to the near exclusion of any other thought.
People have been pondering and arguing over hypnosis for more than 200 years, but science has yet to fully explain how it actually happens. We see what a person does under hypnosis, but it isn't clear why he or she does it. This puzzle is really a small piece in a much bigger puzzle: how the human mind works. It's unlikely that scientists will arrive at a definitive explanation of the mind in the foreseeable future, so it's a good bet hypnosis will remain something of a mystery as well.
“That study changed the whole landscape,” said Dave Patterson, a psychologist at the University of Washington in Seattle, who has been using hypnosis since the 1980s to help burn victims withstand the intense pain that comes with the necessary but excruciating bandage removal and wound cleaning. Since the ’90s, other well-designed, controlled studies have been published showing similar changes in brain activity. In another slightly trippy example, researchers suggested to people in a hypnotic state that the vibrant primary colors found in paintings by Piet Mondrian were actually shades of gray. “Brain-scan results of these participants showed altered activity in fusiform regions involved in color processing,” notes psychologist Christian Jarrett.
Despite briefly toying with the name "rational Mesmerism", Braid ultimately chose to emphasise the unique aspects of his approach, carrying out informal experiments throughout his career in order to refute practices that invoked supernatural forces and demonstrating instead the role of ordinary physiological and psychological processes such as suggestion and focused attention in producing the observed effects.
In hypnosis, patients typically see practitioners by themselves for a course of hourly or half-hourly treatments. Some general practitioners and other medical specialists use hypnosis as part of their regular clinical work and follow a longer initial consultation with standard 10- to 15-minute appointments. Patients can be given a post-hypnotic suggestion that enables them to induce self-hypnosis after the treatment course is completed. Some practitioners undertake group hypnosis, treating up to a dozen patients at a time—for example, teaching self-hypnosis to prenatal groups as preparation for labor.
Braid worked very closely with his friend and ally the eminent physiologist Professor William Benjamin Carpenter, an early neuro-psychologist who introduced the "ideo-motor reflex" theory of suggestion. Carpenter had observed instances of expectation and imagination apparently influencing involuntary muscle movement. A classic example of the ideo-motor principle in action is the so-called "Chevreul pendulum" (named after Michel Eugène Chevreul). Chevreul claimed that divinatory pendulae were made to swing by unconscious muscle movements brought about by focused concentration alone.
Hypnosis is not a psychotherapeutic treatment or a form of psychotherapy, but rather a tool or procedure that helps facilitate various types of therapies and medical or psychological treatments. Only trained health care providers certified in clinical hypnosis can decide, with their patient, if hypnosis should be used along with other treatments. As with psychotherapy, the length of hypnosis treatment varies, depending on the complexity of the problem.