This is a great article by Vaughan Bell:
The ability to be hypnotised seems to be a distinct trait with varied degrees of suggestibility across the population.
Hypnosis is the eccentric uncle of cognitive science. It was once part of the mainstream – studied by scientists and clinicians alike in its 1960s heyday – but it slowly fell into disrepute as it was picked up and popularised by tacky stage hypnotists and quack practitioners in the following decades.
In recent years, hypnosis has seen something of a rebirth, and neuroscience studies using the technique are now regularly published in some of the most respected scientific journals. Curiously, though, it hasn’t shaken off the stigma entirely. While writing this article I contacted several researchers who have published neuroscience studies using hypnosis, and not one replied. The reticence is understandable. Like the study of consciousness 20 years ago, hypnosis is still considered by some to be a “career-limiting move”. Consequently, scientists make sure they stick to the most conservative and orthodox form of research – academic journals, occasional conference presentations, and definitely nothing that hints of hype, or indeed, public exposure.
The lack of wider discussion is a pity, as hypnosis – or rather suggestibility – is a remarkable aspect of human psychology. The ability to be hypnotised seems to be a distinct trait that is distributed among the population, like height or shoe size, in a “bell curve” or normal distribution: a minority of people cannot engage with any suggestions, a minority can engage with almost all, and most people can achieve a few.
The key word here is “engage”, as, contrary to popular belief, hypnosis cannot be used to make people do something against their will, even though the effects seem to happen involuntarily. If this seems paradoxical, a good analogy is watching a movie: you don’t decide to react emotionally to the on-screen story, but you can choose to turn away or disengage at any time. In other words, the effects of the film, just like hypnosis, require your active participation.
The most difficult suggestions to achieve are those which affect the fundamentals of the mind, such as memory and perception, meaning that while highly hypnotisable people can experience temporary hallucinations and amnesia after suitable suggestions, low-hypnotisable people may only be able to experience temporary changes in their volition or movements – such as an arm feeling heavier than usual, perhaps.