‘Catching’ an itch not so much a sign of empathy as a clue to neuroticism

No sensation better captures the powerful interplay between mind and body like the humble itch. A new study turns up copious evidence to suggest that merely seeing someone else scratching can induce itchiness. And it demonstrates that a person’s propensity to “catch” someone else’s itch reveals a lot about his or her personality.

Even more than yawning and laughter, the urge to scratch can be socially contagious, the new research reveals: Among subjects who saw videos of other people scratching themselves, 64% did the same (seeing another yawn reportedly induces contagious yawning in 40% to 60% of cases, and studies have found laughing induces a contagious reaction 47% of the time).

But while many behaviors we mimic--smiling and head-nodding for instance--appear to spring from an impulse toward empathy, a person’s propensity to “catch” another’s itch seems to signal an inclination toward negative feelings, the new study finds.

The study was published Monday in the Proceedings of the National Academies of Science (PNAS).

Itchiness may seem like a frivolous thing to study. But understanding that vaguely unpleasant sensation that propels us to action may shed light on more serious conditions, such as physical pain, major depression and even instances of “delusional parasitosis,” an unfounded belief that one’s skin has been infested (widely called in recent years “Morgellons disease”). Chronic itch has been likened, in its ability to sap a person’s pleasure and energy, to chronic pain. And chronic itch and chronic pain have been linked to depression--a disorder to which those who measure high in neuroticism tend to be highly vulnerable.

The current study put 18 of the study’s 51 participants into a brain scanner to see how their brains responded to viewing others’ itchiness--and to test whether their response was any different when they saw videos of people merely tapping themselves.

Neuroscientists have actually identified something called the “itch matrix”--a cluster of regions scattered throughout the brain that collectively become active when itchiness is induced by the administration of histamines. When subjects in this study watched videos of others scratching themselves, not only did subjects routinely report they felt itchy (as they were in a brain scanner, however, they were urged not to scratch); their brains’ “itch matrix” showed activity in proportion to the intensity of itchiness the subject reported.

The tapping videos evoked no reported itching sensations among participants, the study found (nor, apparently, did it evoke the impulse to tap oneself). Neither did their brains’ “itch matrix” light up in response to videos of people tapping themselves.

Finally, the researchers had all 51 participants fill out several personality inventories that measured such traits as empathy as well as extroversion, agreeableness, conscientiousness, openness and neuroticism. For most “socially contagious” behavior, psychologists have found that a person’s degree of empathy is a good predictor of an individual’s propensity to mimic.

But the authors of the current study found that only a high level of neuroticism--the tendency to feel negative emotions--predicted a person’s likelihood of “catching” an itch after seeing someone else scratch. More empathic people were not more likely to “catch” an itch. In fact, the opposite appeared to be the case: Participants who were less likely to take another’s viewpoint, or to respond compassionately to someone else’s troubles showed a greater propensity to itchiness when they saw someone else scratching.

Yes, the unpleasant feeling that engenders the need to scratch can also be a warning sign that the body’s immune system is fighting a foreign invader (think the hives), or a sign of liver disease, lymphoma or thyroid disease. But far more often, it seems to arise out of nowhere. Reading this, you may find yourself with a sudden, inexplicable urge to scratch. And the more you think about an itch, the more it seems to intensify.