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.