I feel your pain, even though I can’t feel mine

In 1985, Monday Night Football fans looked on as Washington Redskins quarterback Joe Theismann was sacked. The collision was so forceful that it snapped Theismann’s leg, breaking like, as one fan put it, a “stale chopstick.” Most audience members likely empathized with Theismann and sensed his pain, including people afflicted with a rare disorder that prevents them from feeling pain themselves, a new study suggests.

Instead of using past experiences of feeling pain to commiserate, such people likely rely on the ability to imagine the pain of others, suggests the brain-imaging study, published online January 28 in Neuron.

“This fascinating and well-conducted study” gives new insights into the relationship between pain and empathy, comments Marco Loggia of the Athinoula A. Martinos Center for Biomedical Imaging in Charlestown, Mass.

The study suggests that multiple brain regions, including regions involved in emotions, can be recruited to feel empathy for others’ pain. In future studies, Loggia says, it would be interesting to examine other cases when people are exposed to someone else’s feelings without ever having felt such feelings firsthand. “How can humans empathize with a dog that hurt its tail? How can a man understand menstrual pain?” Loggia asks. The answers, he proposes, may lie in the same regions of the brain that allow pain-insensitive people to empathize with others’ pain.

Study coauthor Nicolas Danziger wanted to know whether a person could empathize with an unfamiliar emotional state. Understanding other people’s emotional states, such as pain, is thought to be based on a system in the brain called the mirror system. When someone sees a quarterback break a leg, specific groups of brain cells in the spectator’s brain activate. These nerve cells are the same ones that would activate if the spectator broke his own leg.

Called mirror neurons, these cells are thought to prompt a kind of knee-jerk reaction in the brain in response to seeing others’ pain, a phenomenon researchers call automatic resonance. Put simply, these mirror brain cells don’t distinguish between monkey see and monkey do.

The activity of whole groups of interconnected neurons in one person can mirror that of whole groups of interconnected brain cells in another person, a process called “mirror matching.” Now, scientists know that entire mirror neuron systems can respond to others’ emotions, such as disgust. Seeing a disgusted person elicits mirror matching in the brain of the watcher, where the same group of nerve cells activates as if the watcher were disgusted himself.

Some researchers had proposed that mirror neurons would not exist or not respond correctly when a person witnessed an unfamiliar sensation. To test this idea, Danziger, a neurologist in the Pain Center at the Pitié-Salpêtrière Hospital in Paris, recruited a unique group of subjects.

Some people are born with rare genetic defects rendering them completely insensitive to physical pain. Danziger’s team used fMRI techniques to study the brain responses of such people as they gazed at physically painful situations.

Subjects were shown images of a finger caught in a pair of shears and of a man’s face screwed up in a painful expression. The brains of control subjects who feel pain normally showed activation patterns in two pain-sensing brain regions, the anterior mid-cingulate cortex and the anterior insula.

As it turns out, these pain-sensing regions were similarly activated in the subjects who could not feel pain. “Our first intuition is that we were expecting a huge difference between the two groups. We saw the contrary,” says Danziger.

The results suggest that these brain responses are not mirror matching systems for pain. However, the similarity of brain activation in these regions doesn’t rule out possible mirror matching in other brain regions, says Danziger.

Brain regions like the amygdala, important for emotional processing, might harbor a mirror matching system for pain, he says. The researchers couldn’t assess amygdala activation, due to fMRI interference from nearby bone.

It was in the midline brain structures that the team noticed differences between pain-insensitive subjects and control subjects. When they were able to empathize with others’ pain (as judged by a questionnaire), people insensitive to pain relied heavily on activity in these regions (parts of the prefrontal cortex and the ventral posterior cingulate cortex) involved in formulating emotional perspectives. Only pain-insensitive subjects with high empathy scores had high activity in these brain regions, whereas in control subjects, activity in these regions had little to do with the amount of empathy.

Pain-insensitive people “can only rely on the emotional regions,” says Danziger. “It’s far from automatic.” These people may be relating the physical pain they witness to emotional pain they have felt themselves.

Most likely, the midline brain structures, places where Danziger says “emotional work” is done, and the mirror matching systems both play a role in empathy in regular people.

“I think both mirror neuron areas and midline areas are important for intersubjectivity,” comments Marco Iacoboni, a neuroscientist studying mirror neuron systems at the University of California, Los Angeles.