Mirror Neuron System and Upper-Limb EMG Activity During Reaching Imitation in Stroke Survivors: Comparing Outcomes After Observing Normal vs. Aberrant Movements

PurposeTo assess how brain cortical activity and upper limb (UL) muscle activity associated with the imitation of a UL reaching task differ following action observation of normal and aberrant movement conditions.Materials and MethodsIn this cross-sectional study, 17 individuals who had unilateral stroke were asked to watch a UL reaching task performed with normal and aberrant movement patterns shown with prerecorded videos and then imitate normal movement patterns. Electroencephalographic mu-rhythm activity, a measure of the mirror neuron system (MNS), and the electromyographic amplitudes of four paretic UL muscles (percentage maximum voluntary contraction) were measured during action observation and imitation (AOI) of normal and aberrant conditions. Freidman's ANOVA was used to compare the outcomes across the conditions.ResultsEEG analysis revealed statistically significant suppression of mu-rhythm (demonstrating better MNS activity) during the AOI of normal movement than during aberrant movement conditions at the C3 (p = 0.001) and C4 (p = 0.003) electrodes. Furthermore, the amplitude of percentage maximum voluntary contraction for the supraspinatus muscle significantly increased (p = 0.027) during imitation of the task following observation of the normal movement condition.ConclusionAOI of normal movements resulted in better MNS activity and increased supraspinatus muscle activity than did the observation of aberrant movements. These findings support the incorporation of therapist-guided AOI training focused on normal movement patterns and the avoidance of exposure to aberrant models as a low-cost, neurophysiology-driven adjunct in stroke rehabilitation protocols.Trial RegistrationClinical Trials Registry-India (CTRI) identifier: CTRI/2018/04/013466.