Behavioral evidence of reduced working memory capacity in fibromyalgia patients is not reflected in electrophysiological outcomes

Fibromyalgia is characterized by widespread musculoskeletal pain accompanied by sleep disturbances and cognitive dysfunction, among other symptoms. Patients frequently report difficulties with memory, but objective assessment of these impairments remains limited. This study aimed to evaluate working memory performance in fibromyalgia patients using two established paradigms: the change detection task, which primarily measures storage capacity, and the n-back task, which assesses both storage and manipulation of information.

For the change detection task, the behavioral outcomes assessed were the hit rate, false alarm rate, capacity estimate and response times. The electrophysiological measure evaluated was the contralateral delayed activity. For the n-back, the behavioral outcomes were the same, except for the capacity estimate. Electrophysiologically, the P2 and P3 from the evoked potentials were the outcomes of the task. Behaviorally, results demonstrated that fibromyalgia patients exhibited lower memory capacity than controls (1.90 vs 2.64), in the change detection task, which involved differences in the hit rate and false alarm rate, whereas no behavioral differences were found for the n-back task. In contrast, no differences were found for any of the electrophysiological outcomes in any of the tasks. Taken together, we found evidence supporting a reduction in working memory capacity in fibromyalgia, although it is not reflected in electrophysiological measures.