When an individual scratches an itch, the areas of the brain that involve motor control and reward processing are activated, which is higher in chronic itch patients than healthy individuals, according to a recent study by a Temple University research team led by Professor Gil Yosipovitch.
Chronic itch is a symptom of some skin conditions, could occur as a response to some drugs, and is reported in certain types of cancer. If an itch persists over six weeks’ time, it is classified as chronic. While some patients may experience itching in specific area/s, others might have itching all over their bodies. In the USA, millions of people suffer from chronic itch stemming from various reasons. Research has shown that nerves are the “first responders” to itch and the message is conveyed to the brain.
The study being discussed here attempts to understand changes in the brain when a chronic itch patient undergoes the “itch-scratch” cycle to find relief. The study also elucidates differences in brain activity between healthy and chronic itch patients. For this investigation, a sensation of itch was induced in 10 healthy controls and 10 chronic itch patients by applying cowhage to their right forearms. Subsequently, their brain functions were assessed using functional magnetic resonance imaging (fMRI) to observe brain activity as a result of scratching.
The results showed that:
- ‘Scratching induced pleasurability’ activated the reward zone in the brains of both healthy and chronic itch patients.
- Compared to healthy controls, in chronic itch patients, increased brain activity was also observed in the areas that are associated with motor control and motivation to act.
- The brain areas involved in the “reward circuit” (striatum, cingulate cortex, caudate nucleus and orbitofrontal cortex) were more active in chronic itch patients when compared to healthy participants.
- This hyperactivity of the “reward circuit” may play a role in addictive scratching, the research article states.
Emphasizing the importance of the study’s findings, Dr. Mochiziki, the lead author of the research article, told Temple Health News, “Despite being pleasurable at first, ongoing scratching can lead to an increase in the intensity of itch as well as pain and permanent skin damage. That is why it is important to understand the cerebral activity that may be inducing this pathological scratching behavior."
"Our findings may enable us to identify and advance the understanding of the brain network underlying the itch-scratch cycle in chronic itch patients," continued Dr. Mochizuki. "This understanding could lead to new therapies for these patients."
Written by Mangala Sarkar Ph.D.