A TCD team is studying a condition where senses mix, where a sound can trigger a mental response to colour, writes Ashok Jansari
DOES HEARING the word Monday make you "see" the colour blue or does eating certain types of food make you "taste" shapes? If you are one of these rare individuals then you are a synaesthete and you are experiencing synaesthesia.
Dr Kevin Mitchell, of the Synaesthesia Research Group at Trinity College Dublin, describes synaesthesia as a "mixing of the senses". It is uncommon but not exceptionally rare given it is found in up to 4 per cent of the population and is six times more prevalent in females than males.
While intriguing in itself, the big issue within the field is why two separate "streams" of information (sound and colour for example) get blended such that they seem to co-occur with one automatically triggering the other. Even more importantly, could research into this harmless condition help us understand the origins of clinically debilitating problems such as schizophrenia and autism, Dr Mitchell asks.
Dr Mitchell and his colleague Dr Fiona Newell are part of a multi-disciplinary team incorporating the Smurfit Institute of Genetics and departments of psychology and psychiatry at Trinity College as well as the Nathan Kline Institute for Psychiatric Research in New York. Their extensive three-year project has been funded by grants from the Health Research Board and the Trinity College Institute of Neuroscience.
The team carried out two large studies, the first of which was a nationwide survey that found that over 40 per cent of their sample of synaesthetes have a blood relative who also experiences synaesthesia. Intriguingly, however, the type of synaesthesia (eg, hearing words in colour or tasting shapes) is not inherited, just the predisposition to develop the condition and even more strangely, if one identical twin is a synaesthete, his or her twin won't necessarily be.
This familial study adds to a developmental neurobiological theory that a genetic code involved in synaesthesia leads to "altered wiring", possibly causing greater connections within the brain's neural circuitry in a synaesthete.
So while most individuals keep the information for sound separate from information for colour, for synaesthetes, Dr Mitchell believes, this "separateness is broken down". This results in what he refers to as a "cross-activation" occurring between normally distinct brain areas.
How and why this altered circuitry occurs may give scientists important clues to the "fundamental mechanisms of how the brain gets wired up", according to Dr Mitchell.
Although totally unrelated to synaesthesia (a completely benign harmless condition), there is a suspicion that autism and schizophrenia both involve altered brain circuitry resulting in, for example, an individual suffering from schizophrenia hearing voices.
The Trinity group's second study employed a brain-imaging technique known as electroencephalography (EEG) which involves placing 128 electrodes on a person's skull. This is used to measure electrical activity at the surface of the head and gives us a direct representation of the brain's activity at specific points under the skull while an individual is performing any task.
USING EEG, Dr Mitchell's team showed synaesthetes and non-synaesthetes an array of different visual stimuli, which ranged from letters to abstract patterns. As expected, when shown letters of the alphabet, the synaesthetes showed activation in a part of the brain known to respond selectively to colour information.
More surprisingly, however, the brain activation patterns differed markedly between synaesthetes and non-synaesthetes when they looked at abstract patterns. Their response to these patterns, for example rows of small cubes on a rectangular field, had no previous associations with synaesthesia.
Dr Mitchell reports that the heightened responses in synaesthetes were seen in "low level visual areas" that respond to the form and colour of an image. However, there was a decreased response in pathways responsive to motion.
• Contact synres@tcd.ie or www.tcd.ie/psychology/synres
• Ashok Jansari of the University of East London is on placement at The Irish Times as a British Association for the Advancement of Science Media Fellow