Friday, December 22, 2006

All itches not created equal -- Different parts of brain activated depending on cause

Intense itching and the urge to scratch are symptoms of many chronic skin ailments. A new study conducted by Oxford University researchers has found that different reactions in the brain to two common allergy triggers -- allergens (pollen and dust) and histamine (allergy cells within the body caused by foods, drugs or infection) -- may shed some light on the itch-scratch cycle.

After examining the data obtained at the different itch sites, the different itch scales, and the gender differences between the study populations, the researchers determined that extensive commonalities existed between allergen- and histamine-induced itch. Among them was the extensive involvement of the brain’s motivation circuitry in response to both types of itches.

Researchers also observed differences, including:

* allergen-induced itch intensity ratings were higher compared to histamine;

* perception of itch and changes in blood flow were significantly greater when allergen induced;

* itch intensity perception and the changes in blood flow occurred significantly later in response to allergen, and while the sensations took longer to appear, they were perceived to exist for significantly longer periods;

* itch elicited by allergens activated different parts of the brain, specifically the supplementary motor and posterior parietal areas; and

* the differences found in the orbifrontal regions of the brain imply a compulsion to so something (i.e., scratch) that is very strong in the allergen group. This is presumably due to the heightened intensity of the itch. There are similarities to the activity in this area of the brain and other disorders that display compulsive behavior. This might help to explain why eczema sufferers scratch to the point of harm because they are compelled to do so and cannot help themselves.

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