Paired associative stimulation (PAS) is a non-invasive brain stimulation method that modulate cortical plasticity. Motor imagery (MI) can be used as an alternative to movement execution (ME) after stroke. In this study, we want to compare the motor and electrophysiological effects of a session combining PAS and MI exercises to sessions where only one of the intervention was delivered.

MIPAS is a prospective, randomized, cross-over study. Twenty-three stroke patients with hemiparesis (mean age=52±13 years; time post-stroke=10±22 months; Upper-limb Fugl-Meyer Score (FMS)=28±13/66; Kinesthetic and Visual Imagery score (KVIQ_S)=119±23/140) were included and randomely assigned to one of the three 15 minutes session: PAS+MI; PAS; placebo PAS+MI. The PAS intervention consists of a combination of electrical stimulation of the hemiplegic Extensor Carpi Radialis (ECR) with cortical magnetic stimulation of the ECR cortical representation. In MI condition, the patient is instructed to imagine extension of his hemiplegic wrist and in Placebo PAS intervention, we used a sham probe. We compared the surface variation of the Motor Evoked Potential (MEP) of the ECR and the amplitude of Active Extension (AE) of the hemiplegic side after each session.

In comparison with the other two sessions, significant facilitation associated with motor improvement was observed 15′ after the end of session placebo PAS+MI (ΔPEM_(C)=+62%±96.7%; ΔEA_(C)=+2.9±6.7°). Significant motor improvement were observed after the sessions PAS+MI and PAS (ΔEA_(A)=4.1±8.1°; ΔEA_(B)=5.4±6.1°) but not association with cortical excitability changes. The motor improvement after the session PAS was significantly higher in comparison with that observed after session placebo PAS+MI.

Only the session Placebo PAS+MI seems to induce increased cortical excitability associated with motor improvement, the other sessions inducing only motor effect.