June 18, 2007 -- When you see others laugh or cry, it's often normal to feel the impulse to do the same. But what if watching another person being touched made you experience the sensation yourself?
New research describes people who experience just that. It's a rare condition known as mirror synesthesia, the ability to feel a touch when watching another person being touched.
"Watching another person being touched activates a similar neural circuit to actual touch and, for some people with 'mirror-touch' synesthesia, can produce a felt tactile sensation on their own body," researchers Michael Banissy and Jamie Ward reported in their findings, published in the current issue of the journal Nature Neuroscience.
Synesthesia generally occurs when people experience a crossover in sensory perception, such as hearing colors or seeing musical notes. Figures of its prevalence vary, but some experts say it may affect as many as one in 23 people.
Before the new research, however, mirror-touch synesthesia had been documented in only one person. Now the researchers, from the University College London, have found 10 people with the rare ability to mix sight and touch.
The existence of mirror-touch synesthesia was confirmed using brain scans. Through these scans, Banissy and Ward found that areas in the brains of these people would "light up" when they merely saw pictures of people being touched.
The scientists then developed a tactile test for these so-called synesthetes: What would happen if they were physically touched at the same time they watched another person being touched in a different place?
The scientists asked the participants to ignore the image they saw, which was of a person being touched on his right cheek. At the same time, they touched the participants on the left cheek.
Many times, the synesthetes responded that they felt the touch on both cheeks.
The researchers also found that people with mirror-touch synesthesia had an unusually strong ability to empathize with others.
The synesthetes scored higher than people without synesthesia on the emotional reactivity scale, a specific questionnaire used to evaluate empathy.
"The classical idea about empathy is that we understand others pretty much as scientists understand natural phenomena," said Dr. Marco Iacoboni of the Neuropsychiatric Institute at the David Geffen School of Medicine at UCLA.
"It was thought that we observe and make hypotheses about what will happen, but that was completely wrong, totally wrong."
It turns out that humans learn empathy through simulating the actions of others.
"I see you do something, and my brain pretends that I am in your shoes," Iacoboni said. "I see you unscrewing a bottle cap, and I pretend that I am unscrewing a bottle cap."
This way, humans learn to feel what others are feeling by performing the actions others are doing — in their minds, at least.
Because people with mirror-touch synesthesia showed a heightened sense of emotional empathy, the study's authors concluded that simulation was the path to empathy.
"These results support the idea that people learn to empathize by putting themselves in other people's shoes," the authors said in a news release.
While people with mirror-touch synesthesia have overactive senses of empathy, the research conducted on them may help others who have conditions that limit their ability to relate to others.
According to experts, those with disorders such as autism or Asperger's syndrome may have a difference in mirror neurons, the circuitry in the brain that fires when a person performs an action and when the person observes the same action performed by someone else.
Some scientists theorize that autism might be caused by a malfunction of these mirror neurons. Iacoboni believes that the mirror-touch synesthetes, who have hyperactive brain responses, may offer researchers new insight for helping autism sufferers.
"When we find that people with autism are lacking in these things, we can create new ways to intervene with simple techniques that have beneficial effects for parents," he said.