Synaesthesia is a condition in which there is increased connectivity between the areas of the brain that process information received from each sense organ. This leads to a mingling of the senses: for example, sounds may elicit perceptions of colour in a synaesthete who has increased connectivity between the brain’s visual and auditory pathways.
The first scientific description of the condition was provided by Francis Galton in the 1880s. But one form of the condition, called mirror-touch synaesthesia, was described for the first time only two years ago. People with this type of synaesthesia experience tactile sensations when they observe another person being touched. And a new study published online in Nature Neuroscience shows that mirror-touch synaesthetes are more empathetic than non-synaesthetes.
The study was led by Jamie Ward, of the Department of Psychology at University College London, who first described mirror-touch synaesthesia, and gave the condition its name, in 2005. Together with Michael Banissy, one of his graduate students, Ward recruited 10 synaesthetes who claimed to experience tactile sensations when they observed someone else being touched. In a series of experiments, the authenticity of the synaesthetes were verified. The participants were touched on the cheeks or the hands. At the same, they observed someone else being touched, either on the same part of the body that they were touched, or elsewhere. They were asked to report where they were touched, while ignoring their observations of someone else being touched.
It was found that the synaesthetic participants were much faster than the non-synaesthetes at reporting being touched when their observations corresponded to their own experiences. But the researchers were more interested in the situations when the observations of the synaesthetes did not correspond to their own sensations. They had reasoned that synaesthetes should find it harder than non-synaesthetes to distinguish between the sensations elicited by actually being touched and those elicited by observing someone else being touched. And this was indeed found to be the case: the synaesthetic participants made more “mirror-touch errors” than non-synaeshetic controls. That is, they often reported being touched on the same part of the body as those people they observed, even if they were touched on part of the body and person they observed was touched on a different part.
Banissy and Ward then measured the empathy quotients of their synaesthetic and non-synaesthetic participants. Both the experimental and control groups were asked to respond to a list of statements designed to measure their emotional and social skills. It was found that there was a strong correlation between mirror-touch synaesthesia and empathy – the synaesthetes responded more positively than non-synaesthetes to statements such as “I am good at predicting how someone will feel” and “I get upset when I see people suffering on news programmes.”
A region of the brain called the somatosensory cortex receives inputs from; the body is mapped onto this part of the brain, such that when one is touched, the subregion of the somatosensory cortex corresponding to that part of the body becomes active. It is activity in the somatosensory cortex that leads to the sensation of being touched, and it is now known that observing another person being touched also activates the somatosensory cortex. And several years ago, a neuroimaging study conducted by Ward and his colleagues showed that this region of the brain is hyperactivated in mirror-touch synaesthetes when they observe someone else being touched.
The somatosensory cortex and the areas surrounding it (including the primary motor cortex) are hypothesized to be a major component of the brain’s “mirror system”. The mirror system is composed of neurons which fire not just when one is performing a particular action, but also when one observes another performing that action. Thus, it is believed that these cells are involved in “mirroring” the behaviour of others so that the brain can generate simulations of their experiences. It has further been suggested that the mirror system is crucial for the acquisition of behaviors that are learnt through imitiation, such as language, and that it is impaired in conditions such as autism.
Banissy and Ward show for the first time that the sensations elicited in mirror-touch synaesthetes while observing someone else being touched are indistinguishable from those felt when they are actually touched. The researchers had no difficulty in recruiting participants for their study, and all those involved were actually unaware that they had the condition – they believed that their synaesthetic experiences were completely normal. Mirror-touch synaesthesia may, therefore, be relatively common. Perhaps the condition has gone by another name; the somatosensory hyperactivation that occurs when observing others may cause feelings of discomfort, or even pain, when observing someone being hurt. Perhaps, mirror-touch synaesthesia is in fact the condition formerly known as “squeamishness.”
Banissy, M. J. & Ward, J. (2007). Mirror-touch synesthesia is linked with empathy. Nature Neurosci. doi: 10.1038/nn1926. [Abstract]
Blakemore, S. -J., et al. (2005). Somatosensory activations during the observation of touch and a case of vision-touch synaesthesia. Brain 128: 1571-1583. [Abstract]