Ah, that's the spot: Why scratching brings relief

CHICAGO (Reuters) - Oh, it brings such blessed relief and now
scientists can tell you why -- scratching an itch temporarily shuts
off areas in the brain linked with unpleasant feelings and memories.

Ah, that's the spot: Why scratching brings relief

http://news.yahoo.com/s/nm/20080131/sc_nm/itch_scratch_dc_1

CHICAGO (Reuters) - Oh, it brings such blessed relief and now
scientists can tell you why -- scratching an itch temporarily shuts
off areas in the brain linked with unpleasant feelings and memories.

"Our study shows for the first time how scratching may relieve itch,"
Dr. Gil Yosipovitch, a dermatologist at Wake Forest University Baptist
Medical Center in Winston-Salem, North Carolina, said in a statement.

Prior studies have shown that pain, including vigorous scratching,
inhibit the need to itch. Yosipovitch and colleagues looked at what
goes on in the brain when a person is scratched.

He and colleagues used a technique known as functional magnetic
resonance imaging to see which areas of the brain are active during
scratching. They scratched 13 healthy people with a soft brush on the
lower leg on and off in 30-second intervals for a total of five
minutes.

Scratching reduced activity in the anterior cingulate cortex and the
posterior cingulate cortex -- areas linked with pain aversion and
memory.

And the more intensely a person was scratched, the less activity they
found in these areas of the brain.

"It's possible that scratching may suppress the emotional components
of itch and bring about relief," Yosipovitch said.

But they also found why one scratch often begets another.

Scratching increased activity in the secondary somatosensory cortex, a
pain center, and in the prefrontal cortex, which is linked with
compulsive behavior.

"This could explain the compulsion to continue scratching,"
Yosipovitch said.

The researchers noted that the study is limited because people were
not scratching in response to an actual itch.

But they said understanding what goes on in the brain may lend clues
about how to treat people tormented by chronic itch, including people
with eczema and many kidney dialysis patients.

The study, which appears online in the Journal of Investigative
Dermatology, was paid for by the National Institutes of Health.