- NEW YORK (AP) -- Why is it so hard to tickle yourself? Because one part
of the brain tells another: "It's just you. Don't get excited,"
say researchers who watched the brains of people trying to tickle themselves.
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- The killjoy is the cerebellum, found
in the lower back of the brain, the researchers suggest.
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- The brain is already known to predict
what a person will feel when his or her body does something. That way,
it can ignore expected sensations like pressure on the soles of the feet
while walking, and save its attention for more important things, like the
feeling of a foot bumping a stone.
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- Prior studies implicated the cerebellum
in telling the brain what to expect from the body's own movements.
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- The study on self-tickling was reported
in the November issue of the journal Nature Neuroscience by researchers
including Ph.D. student Sarah-Jayne Blakemore at University College London.
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- "I think it's a wonderful step forward"
in understanding how the body monitors its actions, said Deborah Yurgelun-Todd,
director of the cognitive neuroimaging laboratory at McLean Hospital in
Belmont, Mass.
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- But it's too soon to say whether the
cerebellum is the only brain region involved in dampening the tickle sensation,
she said.
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- Some other brain scientists were skeptical
of the finding. Allan Smith of the University of Montreal said his monkey
studies disagree with the new research on how the cerebellum reacts to
a touch on the hand.
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- For the new study, six volunteers lay
on their backs in a brain-scanning machine with their eyes closed. Nearby
was a device with a piece of soft foam attached to a plastic rod. When
the rod moved up and down, it tickled the volunteers' left palms with the
foam.
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- With the brain scanner running, the volunteers
and an experimenter took turns moving the rod, so the volunteers were either
tickling themselves or being tickled. On some occasions, the foam was secretly
removed so that the volunteers would move the rod with their right hands
but feel nothing on their left hands.
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- The researchers compared activity in
different parts of the brain during the various experimental situations.
The results suggest that during self-tickling, the cerebellum tells an
area called the somatosensory cortex what sensation to expect, and that
this dampens the tickling sensation, they said.
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