Background/Purpose: The primary symptom of fibromyalgia (FM) is chronic widespread pain; however, patients report additional symptoms including decreased concentration and memory. Deficits are seen mainly in tests of working memory (WM) and executive functioning. WM is a cognitive system that involves the ability to store and manipulate mental information for a short period of time, as occurs in the 2-back task. Versions of this task have been used extensively in functional neuroimaging studies of WM. Chronic pain may interfere with cognitive performance, but the neural correlates of this interference remain unclear. We hypothesized that FMs would perform worse on the 2-back task relative to healthy controls (HC), with neural-based changes in blood-oxygen-level-dependent (BOLD) signal.

Methods: 16 FM patients completed a randomized double-blind two-period cross-over study of milnacipran versus placebo. Data reported here are from pre-drug baseline assessment. 13 age and gender matched healthy controls (HC) also participated. Participants performed five blocks of the 2-back task (with 0-back as a control) while in the fMRI scanner.  All fMRI data were pre-processed using SPM5.  Our regressors of interest (2-back and 0-back) were convolved with the hemodynamic response function and applied to voxel-wise statistics. Corresponding contrast images (2back>0back) were then entered into a 2^nd level analysis (two-sample t-test) to delineate differences in brain activations between the groups. Regions of interest showing significant changes in BOLD activation during the 2-back task were extracted and analyzed using SPSS 19. 

Results: Behavioral results showed no overall difference between FM and HC groups on the 2-back task; however, there was an interaction with block (F(4, 24)=2.8, p<.05), such that FM patients showed better accuracy during the first block, but did not improve over time.  In contrast, HC subjects improved and by the final block were more accurate than FM patients. While performing the task in the scanner, FM patients displayed significantly less BOLD activity within the left-mid insula (FMConclusion: FM patients displayed reduced activity in the insula, cingulate, and primary somatosensory cortex during a working memory task, when compared to HCs. Behaviorally, FM patients showed no improvement in performance over time, whereas HCs improved.  The results are consistent with a “competing demands” problem with neural resources in FM patients.  It appears as though perception and processing of pain activates areas of the brain that are also involved in cognition, including inhibition and attention networks involved in cognitive executive function, making these networks less available for cognitive tasks.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/functional-magnetic-resonance-imaging-of-working-memory-in-fibromyalgia-support-for-a-competing-demands-theory-of-cognitive-function-in-chronic-pain/