Shared neural signatures in Functional Neurological Disorder and Chronic Pain: a multimodal narrative review.

Background: Functional neurological disorder (FND) frequently co-exists with chronic pain (CP), notably nociceptive and nociplastic (primary) pain disorders. The considerable overlap implies shared underlying mechanisms because of their similar clinical and epidemiological profiles. Although standard neuroimaging and electrophysiological tests typically show normal results in both FND and primary pain disorders, recent advancements in neuroimaging techniques have begun identifying neural biomarkers common to both conditions, though these findings remain preliminary and require further exploration.

Method: We performed a detailed literature review of studies investigating neural activity in FND and chronic pain using electroencephalogram, magneto-encephalography, functional MRI, positron emission tomography and single photon emission computed tomography. Given the diverse nature of the reviewed studies, the synthesis is presented narratively.

Results: Despite methodological differences, convergent data suggest disrupted neural networks across both FND and CP. Common findings include (1) hyperactivation of sensorimotor networks, (2) altered activity within the default mode network-a critical region for self-referential thought-and (3) dysfunction in emotional processing regions, notably the anterior cingulate cortex and insula. Thalamocortical dysrhythmia was identified as a potential unifying concept, characterised by abnormal theta and beta oscillations that enhance pain perception in CP and trigger functional symptoms in FND. Both conditions also exhibit reduced alpha oscillations, likely amplifying sensory sensitivity and emotional responsiveness.

Conclusion: This review highlights shared neural abnormalities (Triple Network model) and introduces thalamocortical dysrhythmia as a novel explanatory framework linking FND and CP. Future research should target populations with coexisting disorders, potentially paving the way for innovative treatments, including hypnosis and neuromodulation/neurofeedback.