BehindTheMedspeak: Why it feels so good to scratch that itch

In a landmark paper published online on January 31, 2008 in the Journal of Investigative Dermatology, scientists demonstrated for the first time ever, using real-time brain imaging technology, what happens in the brain when we scratch.

Long story short: "... scratching actually supresses brain activity associated with bad feelings and memories. Giving in to scratching also stimulates parts of the brain associated with compulsive behavior — which could explain why some of us keep at it even when we know we shouldn't," wrote Jean P. Fisher in a February 4, 2008 McClatchy Newspapers story, which follows.

Studying the itch to scratch

Ah, that's the spot.

Everyone with an itch — or a dog — knows how blissful it is to scratch, and how hard it can be to stop. Now researchers at Wake Forest University Baptist Medical Center think they know why.

In a first-ever study, the scientists used imaging technology to look at what happens in the brain when we scratch. They found that scratching actually suppresses brain activity associated with bad feelings and memories. Giving in to itch also stimulates parts of the brain associated with compulsive behavior — something that could explain why some of us keep at it even when we know we shouldn't. Doctors advise against scratching, which can damage the skin.

The average person with a mosquito bite probably doesn't need to know all that, acknowledges Dr. Gil Yosipovitch, a dermatologist and itch specialist who led the Wake Forest team.

But he said the new findings, which were published online Thursday in the Journal of Investigative Dermatology, may point the way to new treatments for the itchiest among us — people with hives, poison ivy and chronic conditions such as eczema and psoriasis. Severe itch is also a misery for cancer and kidney patients, who develop itch as a side effect of treatment.

Knowing what parts of the brain involved in itching and scratching may suggest medications known to target the same parts of the brain, for example.

"I see these patients in real life," said Yosipovitch. "There are millions of them and they suffer."

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Consider one more time the following sentence: "They found that scratching actually suppresses brain activity associated with bad feelings and memories."

If that's the case with scratching, isn't it possible that behaviors such as cutting and other forms of self-mutilation demonstrate variations on this theme?

Here's the abstract of the scientific paper cited above, by Gil Yosipovitch and colleagues from the Wake Forest University School of Medicine.

The Brain Processing of Scratching

Neuroimaging studies have examined the neural networks activated by pruritus but not its behavioral response, scratching. In this study, we examine the central sensory effects of scratching using blood oxygen level-dependent functional magnetic resonance imaging (fMRI) in 13 healthy human subjects. Subjects underwent functional imaging during scratching of the right lower leg. Scratching stimulus was started 60 seconds after initiation of fMRI acquisition and was cycled between 30-second duration applications of scratching and 30-second duration applications of no stimuli. Our results show that repetitive scratching induces robust bilateral activation of the secondary somatosensory cortex, insular cortex, prefrontal cortex, inferior parietal lobe, and cerebellum. In addition, we show that the same stimulus results in robust deactivation of the anterior and posterior cingulate cortices. This study demonstrates brain areas (motor, sensory, and non-sensory) activated and deactivated by repetitive scratching. Future studies that investigate the central effects of scratching in chronic itch conditions will be of high clinical relevance.

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Bonus: Read the entire article, including figures and tables, here.

The legend for the figure just above: "ACC activity is inversely related to the perceived intensity of scratch. There was a significant correlation between perceived scratch intensity and bilateral deactivation of the ACC (P=0.02). These images are located at x_2 mm, y_18 mm, and z_34 mm in standard stereotaxic space. Blue represents brain deactivation."

The legend for the figure heading this post: "Brain activation during scratching stimuli. These images are located at x_2 x_28 mm, y_-18, y_-26, y_-64 mm, z_-8 mm and z_14 and z_22 mm in standard stereotaxic space. Red represents brain activation, whereas blue represents brain deactivation."