Dissecting the precise nature of itch-evoked scratching

Itch is a discrete and irritating sensation tightly coupled to a drive to scratch. Acute scratching developed evolutionarily as an adaptive defense against skin irritants, pathogens, or parasites. In contrast, the itch scratch cycle in chronic itch is harmful, inducing escalating itch and skin damage. Clinically and preclinically, scratching incidence is currently evaluated as a unidimensional motor parameter and believed to reflect itch severity. We propose that scratching, when appreciated as a complex, multidimensional motor behavior, will yield greater insight into the nature of itch and the organization of neural circuits driving repetitive motor patterns. We outline the limitations of standard measurements of scratching in rodent models and present new approaches to observe and quantify itch-evoked scratching. We argue that accurate quantitative measurements of scratching are critical for dissecting the molecular, cellular, and circuit mechanisms underlying itch and for preclinical development of therapeutic interventions for acute and chronic itch disorders.

Automated summary

This article discusses the relationship between itch and scratching, proposing that scratching should be viewed as a complex multidimensional motor behavior to gain greater insight into the nature of itch. The limitations of standard measurements of scratching in rodent models are outlined, along with new approaches to observe and quantify itch-evoked scratching. Accurate quantitative measurements of scratching are deemed critical for understanding the molecular, cellular, and circuit mechanisms underlying itch, as well as for developing therapeutic interventions for acute and chronic itch disorders.