Objective: To test whether beta power remains abnormally raised during motor preparation in functional movement disorders (FMD) patients.

Background: Excessive attention towards movement control is considered a key pathophysiological feature of FMD. Patients tend to perform worse when a movement can be highly predicted.

Beta oscillations decrease before normal movements and provide an index of motor attention. Therefore, here, we aimed to test whether beta remains abnormally raised during motor preparation as a marker of this excessive attention in FMD.

Methods: We analyzed beta-frequency cortical oscillations during a pre-cued choice reaction time (RT) task with varying cue validity (50% or 95% congruence between preparation and go cues) and focused on action preparation prior to the go cue. At baseline, we compared FMD patients with healthy controls (HC). FMD patients then underwent physiotherapy-based treatment. At follow-up, we compared FMD “responders” with “non-responders” to physiotherapy.

Results: In contrast to the HC group, FMD subjects showed no speed improvement in the predictable cueing condition (95% congruence) as compared with unpredictable cueing condition (50% congruence).

Furthermore, during action preparation, FMDs showed less beta desynchronisation than HC. Importantly, in 95% congruence conditions, HC showed faster contralateral beta desynchronisation [slope -0.045 (95CI -0.057 -0.033)] relative to the ipsilateral side [slope -0.033 (95CI -0.046 -0.021)] (p-value < 0.001), and also a trend for reaching lower absolute contralateral beta power [mean -0.482 (95CI -0.827 -0.137)] relative to the ipsilateral side [mean -0.328 (95CI -0.673 0.016)] (p-value 0.069). Crucially, this was not the case for FMD, or for 50% predictable trials.

At follow-up, FMD responders were faster than FMD non-responders.  Importantly also, only these responders showed beta desynchronization during motor preparation.

Conclusions: Persistent beta synchronization and lack of lateralized beta desynchronization during motor preparation are signatures of abnormal explicit movement control in FMD. We propose that abnormal self-directed attention in FMD, which is associated with an explicit mode of motor control, might interfere with beta desynchronization and impair motor performance.

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MDS Abstracts - https://www.mdsabstracts.org/abstract/explicit-movement-control-in-functional-movement-disorders-is-characterized-by-reduced-lateralized-beta-desynchronisation/