Cortical reorganization after motor imagery training in chronic stroke patients with severe motor impairment: A longitudinal fMRI study

Introduction: Despite its clinical efficacy, few studies have examined the neural mechanisms of motor imagery training (MIT) in stroke. Our objective was to find the cortical reorganization patterns after MIT in chronic stroke patients. Methods: Twenty stroke patients with severe motor deficits were randomly assigned to the MIT or conventional rehabilitation therapy (CRT) group, but two lost in the follow-up. All 18 patients received CRT 5 days/week for 4 weeks. Nine subjects in the MIT group received 30-min MIT 5 days/week for 4 weeks. Before and after the interventions, the upper limb section of the Fugl-Meyer Scale (FM-UL) was blindly evaluated, and functional magnetic resonance imaging was administered while the patients executed a passive fist clutch task. Results: Two cortical reorganization patterns were found. One pattern consisted of the growth in activation in the contralateral sensorimotor cortex (cSMC) for most patients (six in the MIT group, five in the CRT group), and the other consisted of focusing of the activation in the cSMC with increasing of the laterality index of the SMC for a small portion of patients (three in the MIT group, one in the CRT group). When we applied correlation analyses to the variables of relative ΔcSMC and ΔFM-UL in the 11 patients who experienced the first pattern, a positive relationship was detected. Conclusions: Our results indicate that different cortical reorganization patterns (increases in or focusing of recruitment to the cSMC region) exist in chronic stroke patients after interventions, and patients may choose efficient patterns to improve their motor function.