Pathophysiology of functional (psychogenic) movement disorders

This thesis describes a series of studies involving healthy subjects, carefully selected patients with functional movement disorders and organic movement disorders, in which different aspect of the mechanism underlying functional movement disorders were explored: 1. The presence of physical precipitating factors at onset of functional movement disorder by using semistructured interviews. I found that most patients with functional movement disorder have a clear physical event prior to the onset of functional symptoms. 2. The presence of a “jumping to conclusions” reasoning style that may predispose patients with functional movement disorder to accept new hypothesis on the basis of less evidence. They requested less evidence that healthy controls to make a judgement, which is here suggested to influence the manner in which they process novel sensory data occurring during triggering events. 3. The role of attention in symptoms production by using different motor tasks in which the predictability of movements as well as the effect of explicit and implicit strategies in motor control were manipulated. Motor impairment in patients with functional movement disorder was found to be related to the employment of explicit strategies or when pre-planning movements is possible. 4. The intensity and duration of tremor in patients with functional tremor in a real life situation using accelerometers. They were found to fail to perceive 6 that tremor is not present most of the time compared with patients with organic tremor. 5. Finally, I explored the phenomenon of the sensory attenuation using a force-matching task as a measure of sense of agency for movement in these patients. Patients with functional movement disorders have an abnormal sensory attenuation for movement, which may help to explain the lack of agency for the abnormal movement. These results contribute to the understanding of the mechanisms underlying functional movement disorders and by extension, other functional neurological symptoms, and demonstrate that they are amenable to neuroscientific study

Abnormal beta power is a hallmark of explicit movement control in functional movement disorders.

OBJECTIVE: To determine whether sensorimotor beta-frequency oscillatory power is raised during motor preparation in patients with functional movement disorders (FMD) and could therefore be a marker of abnormal "body-focused" attention. METHODS: We analyzed motor performance and beta-frequency cortical oscillations during a precued choice reaction time (RT) task with varying cue validity (50% or 95% congruence between preparation and go cues). We compared 21 patients with FMD with 13 healthy controls (HCs). RESULTS: In HCs, highly predictive cues were associated with faster RT and beta desynchronization in the contralateral hemisphere (contralateral slope -0.045 [95% confidence interval (CI) -0.057 to -0.033] vs ipsilateral -0.033 [95% CI -0.046 to -0.021], p < 0.001) and with a tendency for reaching lower contralateral end-of-preparation beta power (contralateral -0.482 [95% CI -0.827 to -0.137] vs ipsilateral -0.328 [95% CI -0.673 to 0.016], p = 0.069). In contrast, patients with FMD had no improvement in RTs with highly predictive cues and showed an impairment of beta desynchronization and lateralization before movement. CONCLUSIONS: Persistent beta synchronization during motor preparation could reflect abnormal explicit control of movement in FMD. Excessive attention to movement itself rather than the goal might maintain beta synchronization and impair performance

Sensory Attenuation Assessed by Sensory Evoked Potentials in Functional Movement Disorders.

BACKGROUND: Functional (psychogenic) movement disorders (FMD) have features associated with voluntary movement (e.g. distractibility) but patients report movements to be out of their control. One explanation for this phenomenon is that sense of agency for movement is impaired. The phenomenon of reduction in the intensity of sensory experience when movement is self-generated and a reduction in sensory evoked potentials (SEPs) amplitude at the onset of self-paced movement (sensory attenuation) have been linked to sense of agency for movement. METHODS: We compared amplitude of SEPs from median nerve stimulation at rest and at the onset of a self-paced movement of the thumb in 17 patients with FMD and 17 healthy controls. RESULTS: Patients showed lack of attenuation of SEPs at the onset of movement compared to reduction in amplitude of SEPs in controls. FMD patients had significantly different ratios of movement onset to rest SEPs than did healthy controls at each electrode: 0.79 in healthy controls and 1.35 in patients at F3 (t = -4.22, p<0.001), 0.78 in healthy controls and 1.12 at patients C3 (t = -3.15, p = 0.004) and 0.77 in healthy controls and 1.05 at patients P3 (t = -2.88, p = 0.007). CONCLUSIONS: Patients with FMD have reduced sensory attenuation as measured by SEPs at onset of self-paced movement. This finding can be plausibly linked to impairment of sense of agency for movement in these patients

Motivational modulation of bradykinesia in Parkinson's disease off and on dopaminergic medication.

Motivational influence on bradykinesia in Parkinson's disease may be observed in situations of emotional and physical stress, a phenomenon known as paradoxical kinesis. However, little is known about motivational modulation of movement speed beyond these extreme circumstances. In particular, it is not known if motivational factors affect movement speed by improving movement preparation/initiation or execution (or both) and how this effect relates to the patients' medication state. In the present study, we tested if provision of motivational incentive through monetary reward would speed-up movement initiation and/or execution in Parkinson's disease patients and if this effect depended on dopaminergic medication. We studied the effect of monetary incentive on simple reaction time in 11 Parkinson's disease patients both "off" and "on" dopaminergic medication and in 11 healthy participants. The simple reaction time task was performed across unrewarded and rewarded blocks. The initiation time and movement time were quantified separately. Anticipation errors and long responses were also recorded. The prospect of reward improved initiation times in Parkinson's disease patients both "off" and "on" dopaminergic medication, to a similar extent as in healthy participants. However, for "off" medication, this improvement was associated with increased frequency of anticipation errors, which were eliminated by dopamine replacement. Dopamine replacement had an additional, albeit small effect, on reward-related improvement of movement execution. Motivational strategies are helpful in overcoming bradykinesia in Parkinson's disease. Motivational factors may have a greater effect on bradykinesia when patients are "on" medication, as dopamine appears to be required for overcoming speed-accuracy trade-off and for improvement of movement execution. Thus, medication status should be an important consideration in movement rehabilitation programmes for patients with Parkinson's disease

Ratio of SEPs amplitude at the onset of movement and at rest in patients and controls.

<p>Ratio of SEPs amplitude at the onset of movement and at rest in patients and controls.</p

Demographic and Clinical profile of the Participants.

<p>Demographic and Clinical profile of the Participants.</p

Amplitudes and latencies of representative SEPs peaks at rest in patients and controls.

<p>Values are mean ± standard deviation [standard error of the mean].</p><p>Amplitudes and latencies of representative SEPs peaks at rest in patients and controls.</p