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HORROR films are simply a disconcerting watch for the majority of us, but for Jane Barrett they are literally torturous. She writhes in agony whenever the actors on the screen feel pain. 鈥淲hen I see violence in films I have an extreme reaction,鈥� she says. 鈥淚 simply have to close my eyes. I start to feel nauseous and have to breathe deeply.鈥�

She is just one of many people who suffer from a range of disorders that give rise to 鈥渆xtreme empathy鈥�. Some of these people, like Barrett, empathise so strongly with others that they experience the same physical feelings 鈥� whether it鈥檚 the tickle of a feather or the cut of a knife. Others, who suffer from a disorder known as echopraxia, just can鈥檛 help immediately imitating the actions of others, even in inappropriate situations.

Far from being mere curiosities, understanding these conditions could have many pay-offs for neuroscience, such as illuminating conditions like phantom pain. They may even help answer the age-old question of whether empathy really is linked to compassion.

There is a general consensus that empathy-linked conditions arise from abnormalities in the common mechanisms for empathy found in all humans: although few of us experience sensations as powerful as Barrett鈥檚, we all wince at a brutal foul on the football field and feel compassion for someone experiencing grief. Many studies have suggested that our capacity for empathy arises from a specific group of neurons, labelled mirror neurons. First discovered in macaque monkeys, they are situated in and around the premotor cortex and parietal lobe 鈥� regions that span the top of the brain near the middle of the head. These neurons fire both when you perform an action and when you see someone else perform that action.

Although the challenges inherent in placing electrodes in people鈥檚 brains have so far made it difficult to prove convincingly that individual neurons also act like this in humans, fMRI scans have supported the idea that certain populations of neurons do seem to behave in this mirroring fashion.

Compulsive imitation

Put simply, this means that at some level we mentally imitate every action we observe, whether it鈥檚 a somersault or a look of disgust. The popular theory has it that this imitation allows us to put ourselves in the place of those around us, to better interpret their behaviour. This hypothesis has been consistently supported by numerous tests, with empathy scores strongly correlating with the behaviour of the brain鈥檚 mirror-circuits. 鈥淗ow empathetic we are seems to be related to how strongly our mirror neuron systems are activated,鈥� says , a neuroscientist at the University of Groningen in the Netherlands.

Yet if our brains are primed to live out every experience we observe, why is it that we aren鈥檛 all wandering around manically imitating each other鈥檚 actions and absorbing their feelings the whole time? It鈥檚 here that hyper-empathic people, who do exhibit some of these symptoms, enter the picture.

Those with echopraxia, for example, compulsively mimic the actions of everyone they come across, and with a speed and abruptness that suggests it鈥檚 a reflex rather than premeditated. As a result, cognitive neuroscientist at Maastricht University in the Netherlands had long suspected that there must be some inhibition mechanism that prevents us from following through our brain鈥檚 mental rehearsals, one that is absent in echopraxic people.

To put this idea to the test, Bien and her colleagues attempted to recreate the symptoms of echopraxia using transcranial magnetic stimulation (TMS), which can temporarily disturb the electrical activity of neurons in targeted brain areas, preventing them from functioning normally. Figuring that the TMS may be able to turn off their participants鈥� inhibition mechanism, the team showed the subjects specific finger movements, while 鈥渄eactivating鈥� various parts of their brains. The team struck gold when they targeted the left frontal region of the brain, an area known to be involved in motor function. 鈥淲hen we disrupted this area, people started to show an increase in imitative behaviour,鈥� Bien says ().

Could something similar be happening in the other conditions of hyper-empathy? Mirror-touch synaesthetes, for example, cannot watch someone else experience a tactile sensation without feeling it themselves. 鈥淚f I see someone being slapped it registers in my mind as if I was being touched on my own body,鈥� says Fiachra Mckeown, a mirror-touch synaesthete from Ireland.

A squeamish feeling at certain sights is hardly unusual, but cognitive neuroscientists and Jamie Ward of University College London, showed that synaesthetes like Mckeown have genuine difficulty in telling their direct physical experience from their synaesthetic one. The pair asked mirror-touch synaesthetes to report the location of a gentle prod to either their cheeks or hand. At the same time as being touched themselves, the subjects also observed another person being touched on either the cheek or the hand, though not necessarily in precisely the same place as their own stimulation. As expected, the mirror-touch synaesthetes confused the observed and experienced stimulation significantly more than non-synaesthetes.

What could be causing this confusion? One theory has it that there is a threshold of mirror-neuron activation that must be exceeded before you consciously feel the sensation yourself, and that mirror neurons in the synaesthetes exceed this threshold for some reason. Banissy is not convinced by this. 鈥淭he problem is, if it鈥檚 a conscious threshold, now and again you might expect that it would happen to the rest of us,鈥� he says, 鈥渁nd I鈥檓 not sure that people experience the world like this.鈥� Others proposed that touch synaesthesia arises from heightened connectivity between sensory and motor regions of the brain, or a malfunctioning inhibitory mechanism akin to that in echopraxia.

Whose body is it anyway?

There is another intriguing possibility. When mirror-touch synaesthetes observe touch, they have increased activation in their anterior insula (AI) 鈥� activity which the rest of the population lack under those circumstances (). 鈥淭his is the only region that differs between these synaesthetes and you and I,鈥� says Banissy. Since the AI is thought to aid awareness of our inner body, allowing us to experience a sense of body ownership, 鈥渢he activity in the anterior insula might lead to observed touch in others being misattributed as touch to the synaesthete鈥檚 own body,鈥� he says.

While it is doubtless an inconvenience, most mirror-touch synaesthetes don鈥檛 appear to mind the condition, never having known life to be any different. 鈥淲e have one mirror-touch synaesthete who is a nurse. She says she is quite good at shutting off the experience when she鈥檚 at work,鈥� says Banissy.

For some, though, the symptoms are far more severe. 鈥淲hen I witness distress, I start to get this familiar tingling feeling in my phantom leg,鈥� says Barrett, who since having her leg amputated suffers from phantom-limb pain when she sees another person suffering. 鈥淚 also get a general feeling of disquiet and almost helplessness.鈥�

Barrett suffers from a highly specific form of mirror-touch synaesthesia characterised by strong reactions to the sight of painful stimuli. The first reported case of pain synaesthesia came in 2001, when a woman described to a group of neuroscientists how her late husband had felt acute pain whenever he observed her in distress: 鈥淚f I slightly knocked my finger鈥� he would immediately grasp his own finger and say 鈥榙on鈥檛 do that鈥�; he actually felt it,鈥� she said at the time. Inspired by this unusual case, neuroscientists have now discovered many others who report similar symptoms.

鈥淚f I slightly knocked my finger, he would immediately grasp his own: he actually felt it鈥�

The simple existence of people with this type of synaesthesia has informed the debate on how the rest of us deal with other people鈥檚 pain. There was previously a great deal more scepticism that the brain subconsciously mirrors the physical aspect of another鈥檚 pain 鈥� in the same way that it mimics another鈥檚 movements 鈥� because early fMRI scans had suggested only the parts of the brain involved in processing emotion react when we see someone鈥檚 physical suffering.

But fMRI can be fairly imprecise in pinning down subtle changes in brain activity, so researchers have since looked to other experiments for clues to the existence of the physical aspects of empathy. For example, cognitive neuroscientist Alessio Avenanti at the University of Bologna in Italy has shown that the automatic nervous activity in the hand muscles of participants watching a needle pierce another鈥檚 hand is very similar to the activity triggered by a needle piercing their own hand. It鈥檚 by no means conclusive, but the results strongly suggested to Avenanti that the same circuits within the brain must be responsible for sending out the signals to the hand in both scenarios.

Evidence from pain synaesthetes would seem to lend some weight to the idea that the brain mirrors the physical aspects of pain, since it would make sense that their physical sensations would arise through some malfunctioning of this mirror system. 鈥淚t is highly plausible that [sensitivity] for pain is common in all of us, and varies in response to seeing or thinking about another in pain, from tingling through to the actual perception of pain,鈥� says at Monash University in Melbourne, Australia.

There is, however, one key difference between pain synaesthesia and other types of hyper-empathy. Besides having a heightened sensitivity to another鈥檚 pain, all the documented pain synaesthetes shared one other characteristic 鈥� they had all suffered traumatic pain before developing the condition. Many are amputees, and their phantom limb is the site of the pain they feel when faced with another鈥檚 distress ().

Since the condition is not present from birth, Fitzgibbon suggests it might have been the painful experience that somehow heightened their sensitivity to another鈥檚 pain. When we are threatened, our body naturally becomes hypervigilant to pain: our pain threshold lowers, making even small triggers painful, and our pain response increases, making every injury feel larger than it otherwise would. Pain synaesthesia may be a symptom of an abnormal, ongoing hypervigilance that reduces the natural inhibition of the mirror-neuron system, making the people afflicted with it more sensitive to other potentially dangerous situations.

That may be why Barrett finds the sound of her husband鈥檚 power tools distressing 鈥� since they are potentially threatening objects 鈥� and it could also explain symptoms felt by Anton Alers, who has suffered from pain synaesthesia since losing his right leg to gangrene. As you might expect from somebody whose body is stuck with a hypervigilant response, even scenes from light-entertainment TV shows can bring sharp flashes of pain to his phantom limb: 鈥淚 have painful experiences watching programmes such as the Funniest Home Videos TV series, which often shows impact-related events.鈥�

鈥淓ven power tools and light-entertainment TV shows can bring sharp flashes of pain to phantom limbs鈥�

Taken together, these findings support the idea that we all lie somewhere on a scale of empathy dictated by the activity of our mirror neuron systems, which throws up the question of whether we could manipulate this activity to help certain disorders.

People who have experienced trauma such as severe burns or post-traumatic stress disorder may particularly benefit from this knowledge. That鈥檚 because, in these people, the same hypervigilance that may spark pain synaesthesia might instead lead to some kinds of phantom pain not associated with any physical stimulus. 鈥淯ltimately, by elucidating the underlying neural mechanisms we may be able to improve pain-management strategies and trauma counselling,鈥� says Fitzgibbon. The benefits of understanding empathy in autism could also be immense, she adds, if it leads to better diagnosis and support.

One approach to manipulate our mirror systems might involve TMS, which could stimulate or reduce activity in cortical regions that are under or overactive. Another could be behavioural therapy, since many touch-synaesthetes report having some ability to consciously reduce their responses, and other evidence suggests that phantom-limb pain can be reduced through visual tricks.

Beyond medicine, why not increase the empathy in all of us? Popular opinion, after all, holds that empathy leads to kindness and compassion. at Harvard Medical School in Boston, for example, has started studying the link between empathy and psychopathic traits. She conducted an experiment similar to Avenanti鈥檚 study of subjects鈥� physical reaction to videos of painful stimuli. Participants were also asked to complete a psychopathic personality inventory (PPI), a questionnaire designed to probe psychopathic traits such as egocentricity, fearlessness, and the ability to influence and manipulate others.

The result? Participants who scored highest on one particular aspect of PPI, cold-heartedness, showed the least physical identification with the painful videos. 鈥淭hey don鈥檛 have that sense of putting themselves in the situation,鈥� says Fecteau.

Still, manipulating the brain鈥檚 mirror response to increase compassion and empathy could be unpleasant, warns Fecteau, exposing someone to painful experiences they might prefer not to feel. As many hyper-empathisers would testify, it鈥檚 not always comfortable walking in another鈥檚 shoes.

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