Jun 27 2007

Synesthesia – I Feel Your Pain

I recently received the following e-mail:

Dear DR. Novella,

I often listen to the skeptics guide and I have really enjoyed the work you have done in educating people about how to see through logical fallacies. So today I was cruising the web and I found an article that may be of interest to the panel. The article is on synesthesia (http://science.howstuffworks.com/synesthesia.htm) now this just sounds too far out there for me but the article has many references however many of the journals listed have the term “nature” in the title so I am a little skeptical but it still sounds truly scientific and I was wondering if you might have any insight into this interesting phenomenon.

Part of functional skepticism is recognizing red-flags for possible pseudoscience – but spotting red flags is not enough. That is only the beginning of skeptical analysis, not the end. It justified caution, but sometimes these red flags can be deceiving and you have to look deeper to see if a claim is science or pseudoscience.

In this case synesthesia, in its various forms, is a real and very cool set of neurological phenomena.

But first let me address the comment about “Nature” journals. It is true that the terms “nature” and “natural” are so abused in the marketing of woo and pseudoscience that skeptics rightly have a knee-jerk eyebrow-raising reaction to them. It is sad that “nature” has been hijacked by the promoters of nonsense, for the term right belongs to science. Before science was “science” it was “natural philosophy,” and science is primarily the study of nature is all its aspects.

The journal Nature was founded in 1869 by Alexander Macmillan. He was encouraged to do so by Thomas Henry Huxley, who wrote the first article for Nature on the effects of nature on mankind. The founding of the journal was partly inspired by The Origin of Species by Charles Darwin, which created, Huxley thought, the need to educate the public more about science. http://www.nature.com/npg_/company_info/timeline1.html

Nature is now one of the, if not the, most prestigious science journals in the world. It has expanded into the Nature Publishing Group, covering many areas in clinical and natural science, including Nature Neuroscience, where the referenced synesthesia article was published. Any science journal with the name “Nature” at the beginning is part of the Nature Publishing Group and carries with it the history and prestige of Nature.

Turning back to synesthesia, this refers to sensations that originate in the brain from certain types of anomalous sources – ones that involve other sensations either in oneself or others. For example, some people will experience one type of sensory input as if it were another. They can smell colors, or hear tactile sensation. This results from sensory information leaking over into neighboring areas of the brain that are involved in processing another type of sensory information. So in essence, it is a crossed wire in brain, with visual information, for example, going to the auditory cortex and being interpreted as sound.

The article asked about in the e-mail is discussing mirror-touch synesthesia, http://www.ncbi.nlm.nih.gov/sites/entrez a more recently described phenomenon in which some people will feel the sensations that they see other people experience. So if a mirror-touch synesthete sees another person being touched on the cheek they will feel the touch on their own cheek. This has been described in individuals and families, suggesting there are one or more mutations that cause the brain to function this way.

The current working theory is that mirror-touch synesthesia is a product of mirror neurons, also recently discovered. Mirror neurons basically reproduce the emotions we witness in others and are thought to be a key neurological component of empathy. http://www.nature.com/npg_/company_info/timeline1.html Mirror neurons also seem to play a role in mimicking the actions of others – from speech to learned tasks. They are, in short, the neurological substrate of human socialization.

Mirror-touch synesthetes take mirror neurons one step further – they not only emotionally feel the pain of another, they feel the actual pain. This is not surprising, nor does it involve anything supernatural. If a pattern of neurons fire that produce a certain sensation, then you have that sensation, just as if it arose from an external physical stimulus. It is probable, therefore, that mirror neurons in these individuals fire not only those patterns of neurons that represent the emotional content of pain, but the sensory neurons themselves, producing the sensation.

In fact it is possible that most people fire the sensory neurons to some degree. Think about scraping your knee hard against a hard surface. Imagine it in your mind – it does seem to produce a shadow of the sensation itself. Perhaps mirror-touch synesthetes don’t produce a shadow of the witnessed or imagined sensation, but the full thing.

Look for more publications on this topic in the future. Especially with the fMRI technology now available (a technology that itself is rapidly progressing) to image the brain at work, our ability to study how the brain works is accelerating.

These studies also bring up two points I want to emphasize. The first is the extent of genetic variability in the human species. Despite the fact that creationists characterize mutations as almost completely bad and negative – causing genetic information to depart from an imagined (but nonexistent) optimal form – in actuality we see all the time how mutations cause interesting differences in biological function. Mirror-touch synesthetes have an interesting alteration in neurological function. It does not seem to cause them any harm. It is not clear if it provides any benefit either. But the key concept is that they are different. It is just one example of the many ways in which genetic variations causes constant natural experiments in biological function. They are functionally different – not better, not worse, and not hopeless monsters.

But all this functional variability provides raw material for natural selection. As species spread out to various environments, some varieties will be better suited to certain environments, and natural selection will favor them. Occasionally, by chance alone, variability will produce a fortuitous match of ability and environment, and a new strategy of survival may be born.

I mention this because an appreciation for the rich variability of biological function allows us to imagine the plausibility of evolution.

The other point I wanted to emphasize (as I have before on this blog) is that with each new discovery in neuroscience we are demystifying the brain. It turns out that mental function can be reduced largely to the action of neurons. There are emergent phenomena as well that can only be understood by considering the function of the whole brain, but brain function is comprised of regions with specific functions, and of neurons with specific functions. Trying to understand the mind by examining the brain is working out really well, and only getting better and faster.

I can only say that I feel the dualists’ desperation as their beliefs are crashing under the weight of advances in neuroscience.

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