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.