Itch and brain.

Itch is an unpleasant somatic sensation that evokes the urge to scratch. Chronic itch is a severe problem that diminishes quality of life. There are many patients suffering from chronic itch across the world. The brain is the final terminal to receive itch-related signals from the body and plays an important role in perceiving the itch sensation. Thus, to understand the cerebral mechanism of itch perception and how this mechanism differs between healthy subjects and chronic itch patients is important for advancing our understanding on the pathophysiology of chronic itch. Itch is suppressed by scratching or applying painful stimuli. The pleasurable sensation evoked by scratching an itch increases the urge to scratch. Viewing others in itch or imagining the itch sensation may evoke real itch sensations and the scratching response. To understand the mechanisms responsible for these phenomena may provide useful information for the development of treatment of itch and advance our understanding of the cerebral mechanism of itch and scratch. Several functional brain imaging studies have addressed these issues and reported interesting findings. In this review article, the authors discussed the findings of previous studies and how they have advanced our understanding of the central mechanisms of itch, scratch and chronic itch.