Objective: To compare variations in repetitive paired associative stimulation (r-PAS)-induced cortical plasticity among patients with functional movement disorders (FMD) and healthy controls, measuring transcranial magnetic stimulation (TMS)-evoked motor evoked potentials (MEP) amplitude changes induced by r-PAS.

Background: FMD cannot be explained by either brain lesions or dysfunctions. Until recently, FMD were thought to be of psychological origin yet recent studies disclosed several possible abnormalities in neural connectivity and cortical plasticity. Thus, in FMD physical and emotional triggers may result in neuroplastic changes in the central nervous system that can, in turn, perpetuate the symptoms far after the triggering event has ended. r-PAS is a non-invasive brain stimulation protocol inducing prolonged changes of neuronal excitability expression of cortical plasticity that may allow the study of FMD.

Method: Nine patients with aged between 26 and 67 were treated with r-PAS and compared with a healthy-control group. All subjects underwent 90 r-PAS coupled stimuli (median nerve-contralateral motor cortex TMS) at 0,05 Hz at 25ms interstimulus intervals: the MEP amplitude was evaluated immediately and 15’ after r-PAS, then compared with MEP at baseline.

Results: At baseline, no significant differences in TMS motor threshold and in MEP amplitude were detected between the two groups. 15′ after r-PAS, whereas healthy controls showed significantly increased (p=0.032) MEP amplitude from baseline, FMD patients had no significant variation in MEP amplitude.

Conclusion: Because rPAS induced neuroplastic changes only in the control group, our study suggests an impaired r-PAS-dependent neuroplasticity in patients with FMD. It is known that cortical plasticity is related to the balance between glutamatergic and GABAergic systems, hence an impairment in PAS-dependent cortical plasticity may be related to down-regulation of NMDA glutamatergic receptors in FMD patients.
 
This abstract has been previously presented at SIN congress, Bologna, 12-15 ottobre 2019.

References: Stefan K et al. Induction of Plasticity in the human motor cortex by paired associative stimulation. Brain 123(3). 2000, pp. 572–584. Suppa A. et al. The associative brain at work: Evidence from paired associative stimulation studies in humans. Clinical Neurophysiology 128. 2017, pp. 2140–2164. Gulyaeva N.V. Molecular Mechanisms of Neuroplasticity: An Expanding Universe. Biochemistry 82(3). 2017, pp. 237-242

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