White and gray brain matter activity during pain in fibromyaliga patients and healthy controls.

Functional neuroimaging studies have shown that a set of cortical brain regions is typically engaged during noxious stimulation and pain perception in humans. Other studies have focused on cortical brain activation patterns in patients suffering from chronic pain conditions such as fibromyalgia. Recent work has shown that functional MRI signals are also present in white matter. In this study, we present an analysis of white and grey matter functional MRI activation during a block-designed pain stimulus task in cohorts of fibromyalgia patients and healthy controls. Task data and resting-state functional MRI data were collected from female fibromyalgia patients (N = 54) and controls (N = 56). Pain-stimulation task-based functional MRI included noxious pressure of the left shin as well as an appraisal of pain intensity. White and grey matter brain activities related to pain stimulation were analysed in 29 white matter and 200 grey matter regions-of-interest using time-locked activation analysis. In the healthy cohort, we present evidence of functional MRI brain activity in response to processing painful stimuli for a large majority of cerebral white fibre tracts investigated. In contrast, white matter functional MRI activity in the fibromyalgia cohort was limited to the contralateral posterior and anterior limb of the internal capsule as well as the bilateral cerebral peduncles. Pain stimulation and appraisal of pain intensity also resulted in widespread time-locked functional MRI activity in grey matter, such as visual, somatomotor, fronto-parietal attention and frontal networks as well as in the insular cortex. We have shown that white matter functional MRI signal changes localized to thalamocortical projection fibres, which are attributed to sensory and motor neuronal processing, are related to the perception and appraisal of pain in both fibromyalgia patients and healthy controls. Our results suggest that functional MRI of white matter projection fibres provide additional information that goes beyond task-induced functional MRI responses in cerebral grey matter, with a potential to become clinically useful in the future.