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

## TL;DR

This study shows that observing normal movements improves brain and muscle activity in stroke survivors compared to observing abnormal movements.

## Contribution

The study introduces a neurophysiology-based approach to stroke rehabilitation by comparing brain and muscle responses to normal versus aberrant movement observation.

## Key findings

- Observing normal movements led to better mirror neuron system activity than observing aberrant movements.
- The supraspinatus muscle showed increased activity after observing normal movement imitation.
- Therapist-guided training using normal movement models is suggested as a low-cost rehabilitation method.

## Abstract

To 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.

In 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.

EEG 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.

AOI 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.

Clinical Trials Registry-India (CTRI) identifier: CTRI/2018/04/013466.