Applying tiny electric currents across the visual brain altered the experience of synaesthesia.
'Hyper-excitability' in regions of the brain may underlie synaesthesia, an unusual condition where some people experience a 'blending of the senses', Oxford University researchers suggest. The neuroscientists used some of the latest brain stimulation techniques with people who 'see' colours when reading numbers or words, a common form of the condition called 'grapheme-colour synaesthesia'. They investigated activity in the visual-processing part of their brain, and compared it against the brain activity seen in a control group of people without synaesthesia. They found that people with this type of synaesthesia had a higher level of 'excitability' in their primary visual cortex. It took much less stimulation for neurons in this part of the brain to fire. The researchers also showed that changing the excitability, making it harder or easier for the neurons to fire, could increase or lessen the effects of the synaesthesia. 'The hyperexcitability of the visual area may underlie synaesthesia in people who experience colours triggered by words or numbers,' says Devin Terhune, first author on the Oxford University study.
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