In a new study, scientists have established that hypnosis can trigger "synesthetic" experiences - where one sense triggers the involuntary use of another - within an average brain.
The findings ruled out the popular perception that people with synesthesia have extra connections in their brain.
Instead, it suggested that their brains might simply do more 'cross talking', which could be induced by changing inhibitory processes in the average brain.
Synesthesia (known as synesthetes) patients experience abnormal interactions between the senses.
For example digit-color synesthesia, for instance, will experience certain numbers in specific colors (for example, they might experience the number seven as red).
Scientists have attributed the phenomenon to the existence of extra connections between brain areas in synesthesia, but the new study suggests otherwise.
For examining the alternative theory of more cross talk (disinhibition) between brain areas in synesthetes, Cohen Kadosh and colleagues used posthypnotic suggestion to show that people who are not synesthetes can be induced to have synesthetic experiences.
The researchers saw that after inducing digit-color synesthesia, the volunteers had similar experiences to those undergone by real synesthetes in their everyday life.
Also, hypnotized participants failed a catch test which was also failed by real synesthetes: when subjects were hypnotized to experience seven as red (for example) they could not detect the number when a black seven was presented on a red background.
"Our study shows that hypnosis can induce synesthetic experiences in people, suggesting that extra brain connections are not needed to experience cross-sensory interactions and that it is a change in inhibitory processes - more cross talk within the brain - that causes these experiences. This takes us one step closer to understanding the causes of synesthesia and abnormal cross-brain interactions," said Cohen Kadosh.
The study is published in the journal Psychological Science, the premiere publication of the Association for Psychological Society.