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© 2010 American Academy of Neurology The involuntary nature of conversion disorderFrom the National Institute of Neurological Disorders and Stroke (V.V., C.G., N.H., M.B., V.E., M.H.), NIH, Bethesda, MD; and Wellcome Trust Centre for Neuroimaging (V.V.), Institute of Neurology, University College London, UK. Address correspondence and reprint requests to Dr. Valerie Voon, NIH, 10 Center Dr., Building 10, Room 7D42, Bethesda, MD 20892-1428 voonval{at}gmail.com Background: What makes a movement feel voluntary, and what might make it feel involuntary? Motor conversion disorders are characterized by movement symptoms without a neurologic cause. Conversion movements use normal voluntary motor pathways, but the symptoms are paradoxically experienced as involuntary, or lacking in self-agency. Self-agency is the experience that one is the cause of one's own actions. The matched comparison between the prediction of the action consequences (feed-forward signal) and actual sensory feedback is believed to give rise to self-agency and has been in part associated with the right inferior parietal cortex. Using fMRI, we assessed the correlates of self-agency during conversion tremor. Methods: We used a within-subject fMRI block design to compare brain activity during conversion tremor and during voluntary mimicked tremor in 8 patients. Results: The random effects group analysis showed that conversion tremor compared with voluntary tremor had right temporoparietal junction (TPJ) hypoactivity (p < 0.05 family-wise error whole brain corrected) and lower functional connectivity between the right TPJ, sensorimotor regions (sensorimotor cortices and cerebellar vermis), and limbic regions (ventral anterior cingulate and right ventral striatum). Conclusions: The right TPJ has been implicated as a general comparator of internal predictions with actual events. We propose that the right TPJ hypoactivity and lower TPJ and sensorimotor cortex interactions may reflect the lack of an appropriate sensory prediction signal. The lack of a match for the proprioceptive feedback would lead to the perception that the conversion movement is not self-generated.
Abbreviations: C = conversion tremor; DSM-IV = Diagnostic and Statistical Manual of Mental Disorders, 4th edition; FWE = family-wise error; R = rest; TPJ = temporoparietal junction; V = voluntary mimic.
Study funding: The study was supported and conducted at the National Institute of Neurological Disorders and Stroke, NIH. Disclosure: Author disclosures are provided at the end of the article. Received June 11, 2009. Accepted in final form September 16, 2009.
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