Is motor imagery really a window for studying stroke recovery at subacute stage?

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Because of similarities with overt movement execution, motor imagery is considered as a way to study motor recovery after stroke. However, some studies could not correlate motor imagery abilities with motor function at the subacute stage of stroke challenging motor imagery as a substitute to motor execution in these patients. The aim of this study was to compare explicit and implicit motor imagery abilities in stroke patients and in healthy subjects, to correlate those with motor function and investigate the role of lesion side and location on performances. Twenty-two stroke patients at the subacute stage and 22 healthy volunteers performed implicit and explicit motor imagery tasks (Hand Laterality Judgment Task [HJLT], imagined and executed self-paced hand movements) and a motor assessment (maximal grip strength, Jebsen-Taylor Test [JTT]). Differences between healthy subjects and patients and the impact of lesion side and location on motor imagery were studied using ANOVA. Correlation coefficients were used to analyze the relationship between motor imagery abilities and motor function. For implicit imagery in HLJT, stroke patients had slower reaction times ( P ≤ 0.03) and tended to have higher rates of errors ( P = 0.05) but shared similar characteristics (angle effect: P ≤ 0.01) compared to healthy subjects. For explicit imagery, patients were slower than healthy subjects for the affected hand in the executed condition ( P = 0.04) and tended to be slower in the imagined condition ( P = 0.06). Patients and healthy subjects exhibited a temporal congruence ( P ≤ 0.004) except for right-sided strokes ( n = 8) and patients with parietal damages ( n = 9) for the affected hand. Finally, in stroke patients, implicit and explicit imagery performances were not correlated with upper limb function. Caution must be taken to use motor imagery as a tool for monitoring stroke recovery because subacute stroke patients exhibit motor imagery deficits, independently of the severity of motor impairment.