Australasian Science Magazine

Empathy for pain has conceptual commonalities with synaesthesia. Credit: iStockphoto

By John Bradshaw

Empathy for someone else’s pain shares common characteristics with synaesthesia, a sensory condition where individuals can smell music or taste colours.

In the late 1990s I was contacted by a widow who wanted to know whether there was a scientific explanation for some unusual experiences of her late husband. It seemed that whenever he witnessed someone injure themselves, or show sudden pain, he would involuntarily experience immediate and often excruciating pain in the same body part. Thus if his wife accidentally hit her thumb while hammering, he would call out: “Don’t do that, it really hurts”. He really felt it, she said.

After what were probably one or more strokes he became extremely sensitive to touch. Even the slightest hand contact gave him the impression of sharp fingernails. However, if anyone merely commented that she had knocked her finger there was no such empathic experience of pain.

Around this time were the first reports of mirror neuron functions. Initially described in the ventral premotor region of monkeys, these nerve cells not only became activated when the animal grasped or manipulated an object but also when it saw another individual making similar actions. Thus these “mirror neurons” seemed to represent a system that matches observed events to similar, internally generated actions, thereby forming a link between observer and action.

Since those early days, this concept has been fruitfully invoked in explaining the acquisition of skills in primates by observation, and the evolution, and acquisition, of language and other communicative behaviours. I wondered whether the deceased gentleman’s experiences were another possible instance of mirror neuron function, this time in other regions and at a more perceptual level. Consequently we reported it in the medical literature, coining what I thought was an original label for the phenomenon: “allodynia”, from the Greek roots for the words signifying “pain in or from another”.

It turned out to be a fruitful hypothesis for subsequent research in the area, although I later discovered that the term “allodynia” had been previously used to describe a person feeling pain from a single source simultaneously in more than one location. With my co-workers we now prefer to call the phenomenon upon which we are still engaged in research “synaesthesia, or empathy, for pain”.

Synaesthesia is where certain individuals, often related and frequently female (implying a genetic component), simultaneously and more or less vividly perceive sensations through an additional sense. For instance, when hearing a particular musical note or a word such as a particular day of the week, she may at the same time “see” a certain colour.

Music is thereby experienced along with a shifting kaleidoscope of flowing, if subjective, colours. Tuesdays may be “silver” to one such individual (and maybe “purple” to another synaesthete sibling, indicating that it is not just a consequence of a particular family background or upbringing). Fridays may be some other such colour. Importantly, the colours remain consistent for a given individual more or less throughout life.

Almost any combination of senses may be found in synaesthesia – sound/colour, touch/taste, taste/colour – although the first combination is generally the most common, and the effect is only very rarely bidirectional in a given individual. In the late 1990s, such was more or less the state of knowledge of this intriguing phenomenon.

And then, one day, the phone in my office rang. I had left it with a graduate student with whom I was going to discuss her latest findings on bilingualism over lunch. We had locked the door and were awaiting the lift opposite, but the lift never came. The telephone rang insistently, and Barbara suggested that I should answer it in case it was important. I demurred, doubting that this would be the case, but eventually gave way.

It was the weekend editor of a major newspaper, who said that the newspaper’s overall editor had a daughter who had recently been found to be a synaesthete. It had only recently become apparent in her case, possibly because she did not realise that her particular take on reality was in any way unusual or different from that of the rest of us, or perhaps because she was somewhat diffident about admitting to it. “What”, asked the editor, “did I know about it?”

I replied that it was an interesting and little-understood and investigated phenomenon, and I had therefore recently set it as a literature project for some senior undergraduates to investigate. I then remembered Cambridge Professor of Psychiatry, Simon Baron-Cohen, who had used his television programs to gain the cooperation of a very considerable captive audience for his own research. If I took up a somewhat similar media opportunity, and offered to do an article for the newspaper on what was known so far, we could perhaps access a good cross-sectional sample of the Australian population of synaesthetes. I made the offer, it was readily accepted, and I arranged for the editor and a journalist to come to Monash University.

With my former student and colleague, Professor Jason Mattingley, we found an Honours student, Anina Rich, who happened to be looking for a research project. At this point Barbara somewhat shyly made the rather startling admission that she happened to be a synaesthete herself, so we already had a sample of one.

The meeting was a great success, the article duly appeared and we were in business with a comparative flood of volunteers. Anina got her Honours degree and two papers in the prestigious journal Nature, plus several other publications; she went on to do a PhD and a post-doc at Harvard Medical School, and now at Macquarie University she maintains an active interest in this fascinating area.

Shortly afterwards I was contacted by Melita Giummarra of the National Ageing Research Institute at Melbourne University, where she had been working for some time on pain. She had become interested in the intractable pain that can be suffered by many amputees who develop a phantom limb. This is the often compelling illusion that the missing limb is somehow still there, sometimes phenomenologically foreshortened or occupying an unusual or even an anatomically impossible posture, rigid or capable of apparent voluntary movement.

Comparatively little was systematically known about the natural history of either the phantom limb phenomenon itself, or of the often associated pain that often could not be relieved by the usual medications or interventions. Melita wanted to do a PhD in the area to understand and possibly intervene clinically, and a search of the web for a possible research supervisor had thrown up my name.

Profiting from our media success in the synaesthesia study, we put out some newspaper and TV accounts to attract participants. In the ensuing study, Melita ingeniously manipulated reality using various illusions, such as magic knives whose blades harmlessly retreat into the hilt when appearing to stab a prosthesis that the volunteers believe is their own when viewing the faked attack via mirrors.

In the course of Melita’s research she encountered a small number of individuals who described a phenomenon reminiscent of my original allodynia study: whenever they viewed someone experiencing an apparent major threat or pain itself, they too would simultaneously experience an often unpleasant or even severe sensation of empathic pain in the vicinity of the phantom.

Indeed, when I mentioned the phenomenon to my daughter, a physician who had recently herself experienced a very painful and prolonged obstructed labour that ended in an emergency caesarean, she said that ever since then she had experienced sudden and brief pelvic pain of moderate severity and a distinctly unpleasant quality whenever her patients described their own painful experiences.

Such empathy for pain clearly had conceptual commonalities with synaesthesia, and we came to refer to it also as synaesthesia (or empathy) for pain. This phenomenon was clearly worthy of research in its own right, but the only related accounts in the literature seemed to be synaesthesia for touch, where observation of touch causes a tactile sensation in the observer. A mirror system for touch has now been identified in the parietal lobe of the brain.

We were then approached by Bernadette Fitzgibbon from Auckland, who wanted to do a PhD in our area. We enlisted Anina’s collaboration, and her Harvard years had put her in touch with the Walter Reed Army Medical Center in the United States, which has a huge database of the American war wounded. This, along with appropriate local media publicity, gave us more than 2000 volunteers who were amputees as a result of war. We are yet to hear the outcome of a questionnaire sent to these volunteers.

As part of her PhD, Bernadette separately found that 16% of Australian amputees experience pain synaesthesia, which is much higher than the 1–4% incidence rates of other forms of synaesthesia.

Bernadette also published two reviews. The first review explored how mirror systems are involved in understanding another’s experience of pain. In the case of synaesthetic pain, these mirror systems may be disinhibited. This would explain why some people can really “feel” another's pain.

The second review found that the key to this type of synaesthesia is its clear social component, and suggested that existing neurobiological frameworks of synaesthesia and social cognition can be integrated to explain potential mechanisms that underlie synaesthetic pain.

Bernadette also used electroencephalogram and transcranial magnetic stimulation to measure neurophysiological differences in amputees who experience synaesthetic pain. These were the first studies to go further than anectodal reports and directly measure whether there is a difference in the brains of people who experience pain synaesthesia.

There are three morals to this account. First, science can never be a relentless planned objective progression of pre-arranged steps; rather, it resembles a voyage of exploration along an unknown coastline, where we subjectively gamble on taking leads and channels that look promising but may end as cul de sacs, or may even take us on to a whole new ocean of possibilities. Second, chance and a single (nearly missed) phone call can change a number of lives. Finally, at our peril we ignore the media, which alone can disseminate to a wider audience our work both as it deserves and as is our own obligation.