Despite being a major cause of neurological disability, FMD remain poorly understood in their underlying neural mechanisms. Recent studies have suggested that patients with FMD experience impaired control over voluntary movements. 

In the current study, we investigated whether action control is impaired in functional movement disorders (FMD) compared to a healthy volunteer (HV) group, using a Compatibility, Stop and Simon conflict task. Understanding action control in FMD may be helpful in developing more specific diagnostic criteria and better evaluation techniques.

Twenty-three patients with a clinically definite diagnosis of FMD were recruited from the University of Louisville Movement Disorders clinic. Twenty-three age-matched HV were enrolled as controls. Subjects completed questionnaires about demographics, clinical presentation and neuropsychological measures. Motor symptom severity was rated with the simplified functional movement disorder rating scale (S-FMDRS). Cognitive testing was done with three action control tasks (Compatibility, Stop, and Simon Arrows task) that tested action initiation, action cancellation and interference control over actions, using a computer and handheld response grips. 

These results suggest that reactive inhibitory control processes, engaged to suppress interference from the spontaneously activated response impulses in the Simon task, are impaired in FMD patients. FMD does not seem to affect the susceptibility to act on impulses or affect global action cancellation as measured by the Stop task.