Terhune, Cardena and Lindgren published a paper, Disruption of synaesthesia by posthypnotic suggestion: an ERP study, and this paper was discussed by Vaughan Bell in the blog Mind Hacks and in the Guardian newspaper. (here)

Abstract:

This study examined whether the behavioral and electrophysiological correlates of synaesthetic response conflict could be disrupted by posthypnotic suggestion. We recorded event-related brain potentials while a highly suggestible face-color synaesthete and matched controls viewed congruently and incongruently colored faces in a color-naming task. The synaesthete, but not the controls, displayed slower response times, and greater P1 and sustained N400 ERP components over frontal-midline electrodes for incongruent than congruent faces. The behavioral and N400 markers of response conflict, but not the P1, were abolished following a posthypnotic suggestion for the termination of the participant’s synaesthesia and reinstated following the cancellation of the suggestion. These findings demonstrate that the conscious experience of synaesthesia can be temporarily abolished by cognitive control.

In Bell’s discussion, he points out that this is very unexpected “it is equally new to science because no one had suspected that synaesthesia could be reversed.” The synaesthesic effect was being measured by the addition time it took to identify targets that were coloured differently than the colour that the synaesthesic gives them and by the neurological signs of conflict between the two colours (the Stroop effect). Hypnosis can reverse this by eliminating the synaesthesic colour. How?

This trait (hypnotisability) is usually described as “suggestibility” but it is nothing to do with gullibility or being easily led. People susceptible to hypnosis are not more naive, trusting or credulous than anyone else, but they do have the capacity to allow seemingly involuntary changes to their mind and body. The key phrase here is that they “have the capacity to allow” because hypnosis cannot be used to force someone against their will…

When a suggestion is successful, the experience of it seeming to “happen on its own” is key and this is exactly what neuroscientists have been working with – by suggesting temporary changes to the mind that we wouldn’t necessarily be able to trigger on our own. In the case of the two experiments that managed to temporarily “switch off” the Stroop effect in highly hypnotisable people, the suggestion was that the words appeared as “meaningless symbols”. This avoided a clash between the colour and the word because the text suddenly appeared to be gibberish…

Neuroscientists Amir Raz and Jason Buhle suggest hypnosis is really when we allow suggestions to take over from our normally self-directed control of attention that deals with mental self-management, allowing science an exciting tool to “get under the hood” of the conscious mind.

If you find hypnosis intriguing then you will find Bell’s article very interesting, as I did.