The abnormal movements seen in motor conversion disorder are affected by distraction and entrainment, similar to voluntary movement. Unlike voluntary movement, however, patients lack a sense of control for the abnormal movements, a failure of “self-agency.” The action-effect binding paradigm has been used to quantify the sense of self-agency, because subjective contraction of time between an action and its effect only occurs if the subject feels that they are the agent responsible for the action. We used this paradigm, coupled with emotional stimuli, to investigate the sense of agency with voluntary movements in patients with motor conversion disorder.
Twenty patients with motor conversion disorder and 20 age- and gender-matched healthy volunteers used a rotating clock to judge the time of their own voluntary keypresses (action) and a subsequent auditory tone (effect), after completing conditioning blocks in which high, medium and low tones were coupled to images of happy, fearful and neutral faces.
The results replicate those shown previously: an effect following a voluntary action was reported as occurring earlier, and the preceding action later, compared to trials of only keypresses or tones. Patients had reduced overall binding scores relative to healthy volunteers, suggesting a reduced sense of agency. There was no effect of the emotional stimuli (faces) or other interaction effects. Healthy volunteers with subclinical depressive symptoms had higher overall binding scores.
We show that motor conversion disorder patients have decreased action-effect binding for normal voluntary movements compared to healthy volunteers, consistent with the greater experience of lack of control.