Mechanisms of motor dysfunction in functional neurological disorder: A narrative review

One of the characteristic presentations of functional neurological disorder (FND) is with motor symptoms, such as weakness and tremor. While these symptoms are both common and disabling, how they arise at a mechanistic level remains unclear. This review provides an up-to-date account of the underpinnings of motor dysfunction in FND by integrating findings from neuroimaging, physiology, genetic, brain stimulation, and behavioral studies. A literature search was conducted systematically in MEDLINE and PsycINFO, resulting in 168 studies that met our inclusion criteria. Results generally suggest that patients, compared to healthy controls, have difficulties in predicting their own actions and detecting their bodily cues, limiting their capability for action inference. The literature also shows that patients tend to be hypersensitive to stress, accompanied by heightened linkage between their emotion and motor systems, when compared to healthy controls. It is also evident that, relative to controls, patients exhibit distorted action selection and excessive self-monitoring, implying abnormalities in top-down control. We discuss how these abnormal information processing patterns relate to specific motor symptoms experienced by patients with FND, thereby offering a framework that may facilitate the treatment of these symptoms.