Huys, Anne-Catherine Myriam Liliane; (2020) Functional Movement Disorders: Attention, Agency and Beliefs. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This work centers around three aspects of the likely pathophysiology of functional movement disorders: attention, agency and beliefs. The most characteristic, yet intriguing feature of functional neurological disorders is that symptoms typically manifest with attention and improve or disappear with distraction. In an attempt to elucidate what the abnormal attentional focus is, it was manipulated onto different aspects of a reaching movement. Attention in functional tremor seems to be misdirected to the ongoing visual feedback of the movement and this seems to partly contribute to the symptoms. Furthermore, the attention network test indicates that the executive network is impaired. Functional movement disorders share many characteristics with voluntary movements, raising the question whether it is in fact the sense of agency that is the primary abnormality in this disorder. The sense of agency was measured in the context of different attentional foci and with subliminal and supraliminal priming. No abnormalities were detected, although this might have been linked to methodological difficulties. Subliminal priming confirmed that implicit motor control is normal in patients with functional movement disorders. Functional neurological disorders sometimes appear to follow lay beliefs. In order to evaluate if their beliefs about their symptoms are abnormal, functional tremor patients’ perception of their tremor was evaluated in real time and in retrospect. It was found to be accurate and not dissimilar to organic tremor patients’ perception. Attempting to change their beliefs, by modifying the visual feedback they were given did not have any lasting effect on functional nor organic tremor. Dramatic placebo effects are occasionally observed in functional neurological disorders, having led to the conclusion that patients with these disorders are suggestible. A classic placebo analgesia experiment did not show stronger placebo responses in patients with functional neurological disorders than healthy controls, suggesting that the notion of suggestibility is mistaken.

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