A temporal analysis of the central neural processing of itch.

Abstract

Pruritus, or itch, is the most prevalent symptom of allergic and inflammatory skin disease. Although it is known that itch induces activation of a neural network in the brain, the temporal dynamics of the network as well as the pathophysiology and neurobiology are not well understood. The study aimed to elucidate (i) the temporal dynamics of the itch response identified in earlier studies and (ii) the relationship between central and subjective responses to itch. Using a novel time-series analysis, we performed a double-blind, placebo-controlled, randomized, within-subject functional magnetic resonance imaging (fMRI) study of the cerebral processing of histamine-induced itch in healthy volunteers (n = 16) by tracking the 8-min period following a single skin prick. Histamine-induced itch compared with saline resulted in significant area under the curve blood oxygen level dependent (BOLD) signal changes in the middle/superior temporal gyrus and right inferior frontal gyrus/insula. We observed negative itch-induced BOLD signal changes compared with saline in (i) the pregenual anterior cingulate cortex (ACC)/medial frontal gyrus, (ii) subgenual ACC/ventral striatum, (iii) bilateral temporal pole/parahippocampal gyrus and (iv) several regions within the cerebellum. We noted a trend significance in the left precentral gyrus part of the motor cortex. The BOLD signal change in several of these regions correlated with perception of itch intensity. In contrast to other fMRI studies we observed a multifocal negative signal. An improved understanding of both activated and deactivated brain regions during the itch response may in the long term facilitate development of more effective management strategies.