Tones and colours in the brain

A while ago I received an email from a kind blog reader which read as follows:

“I stumbled upon your blog and there is some interesting things on it. But as someone with synaesthesia I was wondering have you done any post on it? My music is full of colours”

The email was from a man called Paul who experiences a rare condition called tone-colour synaesthesia, meaning he consistently experiences sensations of colour when hearing music. At the time I replied to tell him that his was a fascinating condition and that I would love to write about it. But sadly there was no new research out at the time and the idea slipped from my mind.

Luckily a new article has just been published in ‘Neuropsychologia’ which brought me back to this topic. The article seeks to determine the brain correlates of tone-colour synaesthesia.

                  What is synaesthesia? Synaesthetes automatically experience an internally generated stimulus (response) when exposed to a certain perceptual experience (trigger). They may automatically perceive certain words as different colours, certain days as different tastes, or certain sounds as different tactile sensations. You can find more about the details by visiting the UK synaesthesia society. Some famous individuals with synaesthesia include the painter David Hockney, the composer Olivier Messiaen, and the writer Vladimir Nabokov.

Synaesthesia in the form of ‘colour-hearing’ has received a great deal of scientific interest in the past however, there have been few studies of variations of the condition that do not involve a language trigger or response. Tone-colour is one such combination.

Why does it happen? There are two main theories:

1)      There is a direct link between areas of the brain that represent the trigger and the response senses (Direct cross action hypothesis)

2)      The normal feedback mechanisms that prevents our sensory input being jumbled up in the brain in not working properly (Disinhibited feedback model)

The new study: Fourteen auditory-visual synaesthetes and 14 matched controls took part in an fMRI experiment where they were played various isolated tones and chords while images of their brain were scanned.

Synaesthetes showed significantly greater brain activity in an area called the inferior parietal cortex (IPC). The IPC is associated with many tasks including spatial-dynamic processing, mental imagery, attention control and visuo-motor control. It can be thought of as one of the important relay stations in the brain, where input from different sensory areas comes together for processing. The authors suggested that the hyper activity in this area might be behind the extrasensory ‘binding’ that is characteristic of ton-colour synaesthesia – coupling together trigger and response sensory areas via disinhibited feedback.

What about the colour processing area of the brain, known as V4: Do tone-colour synaesthetes show above average activity in this area in response to musical sounds? There was no evidence that brain activity differed between controls and audio-visual synaesthetes in area V4.

This does not mean that there is not V4 activation in other variations of colour synaesthesia, such as word-colour, just that no reliable evidence exists to support this potential explanation for tone-colour synaesthesia.

Conclusion: This new study moves us closer towards understanding one of the less well known variants of synaesthesia, where people reliably see colours in response to musical sounds. The special involvement of the IPC, a multimodal integration area of the brain, supports the hypothesis that colour and music become bound together as perceptual experiences because the area of the brain that fuses these sensory inputs is overactive.

I will leave the final word on this blog to my reader Paul, who so kindly alerted me to this condition in the first place. I asked him if he would mind telling us a little bit about what it is like to have synaesthesia. This is what he said:

“For me music and colour’s are very much woven together. When I write music I always see it as painting in a way that I match the colour’s of certain instruments together and think in terms of “this needs more green or another colour”. When I hear music I see colour’s which is actually harder than it sounds for me to explain in words. Sometimes it’s a kaleidoscope of colour’s and other times its blocks, blobs, circles or just shapes that float and bend into each other. Also the music I like is always the kind I’m drawn to with regard to atmosphere, colour and vibe I get from it”.

Paul is a music composer and his album is out next year called “Hold Onto The Colours”. His website is www.paulmelia.net