Return to home pageWhat's in the news  



Can some people really smell sounds, taste words and see numbers as colours? Can brain science begin explain how and why this happens?


What is synaesthesia?

Synaesthesia is a curious condition where there is a mingling of the senses due to cross-wiring in the brain.


Hearing a musical note for example might cause a person with synesthesia to see a particular colour; C is red, F sharp is blue. Or perhaps the number 2 is always green and 5 always blue.


Other people may taste spoken words, for example, on hearing the word 'table' they might taste apricots, whereas ‘book’ tastes like tomato soup and ‘telephone’ tastes like earwax.


Who gets Synaesthesia?

About 1 in 2000 people have synaesthesia. Recent studies by Simon Baron-Cohen in Cambridge have confirmed synaesthesia is genetic, passed from parent to child.


The slightly different genes of someone with synaesthesia appear to cause adjacent areas of the brain to cross-wire.


What’s happening in the brain?

Colour information is analysed in the fusiform gyrus in the brain’s temporal lobe (area V4).


This is very close to the area of the brain that deals with the physical form of numbers (also in the fusiform gyrus).


It’s thought that a genetic abnormality causes these two areas to cross- wire.


Brain imaging has now confirmed this idea by testing synaesthetes who see numbers as colours. When most people are shown black numbers on a white background, only the number area of their brain becomes active. However, when people with synaesthesia look at the same image, the ‘colour’ area of their brain also activates.


Is there a test for Synaesthesia?

Ramachandran, a famous neurologist and his colleague Ed Hubbard have created this test for the condition.


Look at this image. What do you see?



Most people see lots of 5’s. If they look for longer, they will see that some of the 5’s have been reversed and are 2’s.


Someone with number – colour synaesthesia will immediately see a triangle of 2’s – it would stand out because the 2 and the 5 are seen in two different colours.


What causes synaesthesia?

When you were born, you had far more brain cells than you needed. A period of pruning happens where only the connections and brains cells you need and use survive. This is a normal and vital part of all mammals’ early development.


It’s possible that a gene for synaesthesia causes this pruning process to happen differently results in extra connections and cross-wiring between brain areas.


Click here for interviews with people with synaesthesia


For advice and information, visit the UK Synaesthesia Association’s website