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To: JakeStraw who wrote (23145)9/11/2000 1:02:50 PM
From: SIer formerly known as Joe B.  Respond to of 49844
 
Scientists Answer Ticklish Question
news.excite.com
Updated 9:23 AM ET September 11, 2000

LONDON (Reuters) - Scientists may have unraveled a mystery which has puzzled them and millions of
children for years -- why it is impossible to tickle yourself?

The Daily Telegraph said on Monday the secret lies in the cerebellum, a region at the back of the brain which
predicts the sensory consequences of movements and sends signals to the rest of the brain instructing it to
ignore the resulting sensation.

Sarah-Jayne Blakemore of the University College of London examined six volunteers using magnetic
resonance imaging to scan their brains as their palms were tickled by a machine. The scan was repeated
while they tickled their own palms.

In the first case the machine succeeded in tickling the volunteer because the cerebellum cannot warn the rest
of the brain when the stimulus is external, even if the brain knows it is about to be tickled.

The mechanism once protected us against predators by distinguishing between stimuli that were created
ourselves and those generated externally.

But the system can be fooled.

When the robot used by the volunteers to tickle themselves delayed the action by a fraction of a second, the
tickling sensation was there.

"So it is possible to tickle yourself, but only by using robots," Blakemore said.