Abstract
Functional movement disorders (FMD) are characterized by motor symptoms (e.g., tremor, gait disorder, and dystonia) that are not compatible with movement abnormalities related to a known organic cause. One key clinical feature of FMD is that motor symptoms are similar to voluntary movements but are subjectively experienced as involuntary by patients. This gap might be related to abnormal self-recognition of bodily action, which involves two main components: sense of agency and sense of body ownership. The aim of this study was to systematically investigate whether this function is altered in FMD, specifically focusing on the subjective feeling of agency, body ownership, and their interaction during normal voluntary movements. Patients with FMD (n = 21) and healthy controls (n = 21) underwent the moving Rubber Hand Illusion (mRHI), in which passive and active movements can differentially elicit agency, ownership or both. Explicit measures of agency and ownership were obtained via a questionnaire. Patients and controls showed a similar pattern of response: when the rubber hand was in a plausible posture, active movements elicited strong agency and ownership; implausible posture of the rubber hand abolished ownership but not agency; passive movements suppressed agency but not ownership. These findings suggest that explicit sense of agency and body ownership are preserved in FMD. The latter finding is shared by a previous study in FMD using a static version of the RHI, whereas the former appears to contrast with studies demonstrating altered implicit measures of agency (e.g., sensory attenuation). Our study extends previous findings by suggesting that in FMD: (i) the sense of body ownership is retained also when interacting with the motor system; (ii) the subjective experience of agency for voluntary tapping movements, as measured by means of mRHI, is preserved.
Highlights
The experience of the body as one’s own and the sense of authorship over movements are basic cognitive components of selfrecognition of bodily actions (van den Bos and Jeannerod, 2002; Jeannerod, 2003; Tsakiris et al, 2007; Louzolo et al, 2015)
We did not found significant correlations between agency-statements and disease duration (Active Synchronous Congruent: r = 0.065, n = 20, p = 0.785; Passive Synchronous Congruent: r = 0.345, n = 20, p = 0.136; Active Synchronous Incongruent: r = 0.010, n = 20, p = 0.966; Active Asynchronous Congruent: r = 0.230, n = 20, p = 0.329). This is the first study to investigate the sense of agency over bodily movements, the sense of body ownership, and their interaction in functional movement disorders (FMD) patients by means of the moving Rubber Hand Illusion (mRHI)
The data from the healthy controls confirmed the reliability of the mRHI paradigm in measuring sense of agency and sense of body ownership: the agency-statements and the ownership-statements significantly differed from their respective control statements in the Active Synchronous Congruent, Active Synchronous Incongruent, and Passive Synchronous Congruent conditions
Summary
The experience of the body as one’s own (i.e., sense of body ownership) and the sense of authorship over movements (i.e., sense of agency) are basic cognitive components of selfrecognition of bodily actions (van den Bos and Jeannerod, 2002; Jeannerod, 2003; Tsakiris et al, 2007; Louzolo et al, 2015). This cognitive function is taken for granted in everyday life, it appears to be altered in some pathological conditions, like functional movement disorders (FMD). The motor symptoms look like intentionally produced movements, the patients’ self-report is that the abnormal movements are not under their control (Edwards et al, 2013)
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