THE PATIENT WAS LYING ON THE FLOOR, limbs flailing and eyes rolled back. Joel Salinas, chief neurology resident at Massachusetts General Hospital at the time, had been rushed to the woman’s room to determine whether she was having a seizure. But Salinas brought more than his medical training to her bedside. “The patient, on the floor, her movement—I feel that on my body,” he says, recalling the incident, which occurred earlier this year. “Her facial expressions—I feel that on my body.”

Salinas, 32, now a clinical fellow in behavioral neurology and neuropsychiatry at MGH, has mirror-touch synesthesia (MTS), a phenomenon that causes him to have physical sensations that correspond to what he sees happening to people around him. When Salinas treats someone with a migraine, for instance, the sight of the patient clutching his head can act as a trigger. “That obvious discomfort would be mirrored in my own sensory experience,” says Salinas, who is quick to point out that he doesn’t always feel the patient’s exact throbbing pain; instead, he might experience what he describes as a sort of tingling, which can sometimes grow painful or distressing depending on the extremity of what he’s watching.

Among all people with MTS (about 1% to 2% of the human population) many are even less fortunate. Some do report regularly feeling physical pain when they witness trauma or violence. While Salinas says having MTS can be distracting, he thinks of it as an additional sense, helpful in his job. “The sensations I experience cue me into emotions and pain, so I can be a lot more connected with others and experience a lot more empathy,” he says.

Research suggests that MTS can heighten the capacity for empathy, or the ability to understand how others feel. Moreover, people with MTS seem to be more skilled at identifying emotions associated with facial expressions. As for the woman thrashing on the floor, “I could tell there was a lot of distress on her face,” Salinas says. After getting her back into bed, Salinas’s gentle questioning revealed she was distraught over a cousin’s recent death. His diagnosis was a nonepileptic seizure, which can be brought on by psychological stress. That meant she wasn’t treated with anti-seizure medication, with its risk of adverse effects. In helping to bring a frightening episode under control, says Salinas, “I just tried to make as safe a space as possible for her.”