Functional MRI monitors brain activity during scratching

A deeper understanding of chronic itch and the scratching response in humans is clinically important because they affect the overall health of an individual. More than 30 million Americans suffer from eczema, and nearly half of all kidney dialysis patients are afflicted with moderate to severe itch, 17 percent of whom have a high mortality rate, most likely from itch-related sleep loss.

Researchers at Wake Forest University Baptist Medical Center in Winston-Salem, N.C., have used blood-oxygen-level-dependent functional MRI imaging to help assess the brain activity that occurs during scratching, particularly, the central sensory effects of repetitive scratching. Previous neuroimaging studies have examined neural networks activated by itch, but the scratching response needs further investigation.

As reported online on Jan. 31, 2008, in the Journal of Investigative Dermatology, the study was conducted on 13 healthy subjects who underwent functional imaging while they were scratched on the lower leg with a small brush at different intensities by a member of the research team. The scratching was cycled between 30 seconds of application and 30 seconds of no application, for a total of about five minutes. The passive scratching was used to minimize the motor-related activation associated with self-scratching.

As revealed by the images, the brain areas that were significantly deactivated during the scratching application were associated with unpleasant sensory experiences and memories. The deactivation was lowest when participants reported the most intense scratching. These indications could explain the aspect of relief provided by scratching.

Areas of the brain that were activated by the scratching application were associated with pain and with compulsive behavior, the latter of which could explain the compulsion to continue scratching.

It is possible that a broader understanding of brain processes related to chronic itch could lead to new treatments for the condition, including drugs that could deactivate compulsion-associated brain areas.