British scientists say they've solved a mystery that's been puzzling scientists for years why can't people tickle themselves?

The Daily Telegraph in London reported Monday that the secret lies in the cerebellum, the region of the brain that monitors movement.

Researchers at University College London found that the cerebellum detects self-inflicted touch ahead of time and tells the rest of the brain to ignore the resulting sensation, spoiling the fun of self-tickling.

The UCL team used magnetic-resonance imaging to scan the brains of 16 volunteers who were tickled by a machine and by themselves. The robotic tickler was far more effective because the brain wasn't able to sense when the tickle was coming.

The team then tried letting the volunteers tickle their right hands by activating the robot with their left hands. When the researchers delayed the movement of the machine by a few hundredths of a second they found the volunteers still couldn't tickle themselves.

But when the delay was increased to longer than one fifth of a second, the self-tickling worked.

UCL's Dr. Sarah-Jayne Blakemore says the brain's downplay of sensation to self-touch is a survival mechanism that's evolved so the brain pays proper attention to stimuli from potential predators.