Motor resonance in functional movement disorders: unravelling repertoire-congruent mechanisms of action observation

Functional Movement Disorders (FMDs) are a subtype of Functional Neurological Disorders defined by abnormal involuntary movements such as weakness, tremor, dystonia, gait disturbances, myoclonus, or parkinsonism. These clinical features are typically inconsistent with recognized patterns of organic neurological disease and often fluctuate or change markedly under distraction. FMDs are increasingly conceptualized as disorders of network-level dysfunction, in which aberrant predictive coding, impaired top-down modulation, and disrupted agency mechanisms converge to compromise sensorimotor integration. Within this framework, the mirror neuron system (MNS) constitutes the neural substrate for motor resonance, the process by which observed actions are internally simulated to support action understanding, motor learning, and rehabilitation. A large body of evidence demonstrates that motor resonance is shaped by motor experience: observers show stronger activation of the action observation network (AON) when viewing actions within their own motor repertoire, and this effect extends to neurological populations such as Parkinson’s disease and cerebral palsy, where patients resonate more strongly with pathological models resembling their own motor output. However, whether similar effects characterize FMDs has not yet been systematically investigated. This work addressed whether motor resonance in FMD patients is modulated by the congruence between observed actions and patients’ motor repertoire. Two experimental studies were conducted. In the first, a transcranial magnetic stimulation (TMS) paradigm assessed corticospinal excitability (CSE) in patients with upper limb functional weakness (FW) during the observation of hand movements performed with weak or strong muscular force. Whereas healthy controls showed the expected force-dependent modulation of CSE, FW patients failed to do so. Notably, this effect was most pronounced during the observation of strong actions – movements beyond their motor repertoire – despite preserved explicit recognition of force and effort. The second study employed functional magnetic resonance imaging (fMRI) to examine neural responses in patients with functional gait disorder (FGD) during the observation of healthy versus pathological gait. Whole-brain analyses revealed that, compared to healthy controls, patients exhibited reduced activation of the canonical parieto-premotor network during gait observation, while preserving the overall spatial organization of sensorimotor responses. To further investigate the observed effects, regions of interest (ROIs) were 4 defined based on convergent fMRI evidence from gait execution and stepping paradigms. The aim was to sample neural circuits consistently implicated in locomotor control and previously recognized as key nodes in FMD pathophysiology. ROI analyses showed that FGD patients exhibited stronger activation when observing pathological gait, which resembled their own motor repertoire, whereas healthy controls displayed the opposite pattern, with stronger engagement for the healthy gait. Together, these findings indicate that motor representations in FMD are preserved but expressed with reduced gain, such that motor resonance is preferentially biased toward repertoire-congruent, symptom-related actions. This pattern reflects altered regulation of otherwise intact sensorimotor representations by higher-order cognitive–affective and predictive networks, situating mirror responses within a broader network architecture in which attentional, perceptual, and cognitive–affective processes modulate their expression. Given the marked heterogeneity of symptoms presentation in FMDs, these results also suggest that tailoring rehabilitative interventions to patients’ specific motor repertoire may enhance the effectiveness of AO-based therapeutic interventions.