SAN DIEGO, CALIFORNIA — Researchers at the University of California, San Diego, found a strange case on a woman who laughs hysterically when she sees people being tickled.

Referred to only as TC, the woman laughs uncontrollably when she sees someone getting tickled.

Researchers concluded that the woman suffers from mirror-touch synaesthesia, it's a condition caused by mirror neurons, connectors in the brain that react the same way when an event is experienced or observed.

To make sure TC suffered from mirror-touch synaesthesia, researchers tested the her reactions in various circumstances, like seeing other people touch different surfaces. They also tested her reactions to funny video clips and jokes. It turn out she has a normal sense of humour.

Researcher found that her uncontrollable laughter comes from watching people getting tickled as if she were experiencing the tickling herself. The sensation was so realistic that she would rub her armpits in an attempt to neutralize it

Researcher found approximately 2 percent from population experience mirror - touch synesthesia. Researchers say in observing those with mirror-touch synaesthesia, they they can also learn more about human empathy toward each other.