FMDs require attention to generate the movements, given that distraction leads to decreased movement of the affected body part, while observation or examination leads to increased movement of the affected body part . However, affected individuals lack a sense that the abnormal movements are under voluntary control. While the mechanisms that cause or contribute to FMDs are an area of uncertainty and controversy , an evolving hypothesis is that FMDs result from a combination of predisposing factors including:
●Abnormal self-directed attention
●Abnormal beliefs and expectations
●Abnormal sense of agency (ie, a subjective sense of control) for self-generated movements
●Alexithymia (impaired emotional processing with difficulty identifying and verbalizing internal emotional states)
These processes may lead to an FMD when abnormal predictions regarding movement are triggered by abnormal self-directed attention, leading to movement produced without a subjective, normal sense of voluntary control. In patients with alexithymia, emotional or autonomic symptoms that occur with a triggering event may be misinterpreted as being caused by a physical illness. FMDs represent the complex interaction of psychological and physical expression.
Subtle structural and functional differences between individuals with FMD and controls have been demonstrated using advanced imaging techniques. For example, a voxel-based morphometry analysis showed increased gray matter volume in left amygdala, left striatum, left cerebellum, left fusiform gyrus, and bilateral thalamus among patients with FMD and decreased volume of left sensorimotor cortex. Similar work demonstrated impaired self-agency using functional magnetic resonance imaging (MRI).