An interesting question was submitted to the 'frequently asked questions' page of HypnosisAndSuggestion.org last week. 

Do individual differences in “imaginative suggestibility” provide a simpler explanation than dissociation in explaining responsiveness to hypnotic suggestions?

Dissociation theories of hypnosis (e.g. Hilgard's neodissociation theory, Wood & Bower's dissociated control theory) propose that hypnosis produces 'splits' or dissociations in systems of cognitive control. Consistent with this there is evidence that hypnotisability is higher in patients with 'dissociative' disorders such as post-traumatic stress disorder. However, dissociation theories also predict that healthy people who dissociate more in day-to-day life should also be more hypnotisable. This doesn't seem to be the case: studies correlating hypnotic suggestibility with scores on the dissociative experience scale (DES) aren’t significant. (e.g. Dienes et al, 2009). Given this, it doesn’t seem as though dissociation is terribly valuable when trying to explain responsiveness to hypnotic suggestions.

On the other hand, scores of imaginative suggestibility (non-hypnotic suggestibility) tend to correlate very highly with hypnotic suggestibility (Kirsch & Braffman, 2001). This indicates that the two are related, but there are two issues remaining:
(1) some people argue that 'hypnosis' encompasses a wide domain of suggestion, and that hypnotic and non-hypnotic suggestion are essentially the same thing
(2) ok, you might have explained variance in responsiveness to hypnotic suggestion, but you haven’t explained the mechanism by which people respond to non-hypnotic suggestion.

What seems to be needed is a theory to explain how people respond to non-hypnotic suggestions. Kirsch & Braffman (2001) argue that these factors include: response expectancy, attitudes towards hypnosis, fantasy proneness, absorption, and go/no-go reaction time. However, they caution that these variables do not account for all of the variability in non-hypnotic suggestibility. It is possible that there is an underlying ability, perhaps with a genetic contribution to suggestibility (Raz, 2008), or associations between suggestibility and the size of certain brain regions (Horton et al, 2004). 

If you have any comments about this, or would like to submit a question, feel free to get in touch.