Effects of mirror-box therapy on modulation of sensorimotor EEG oscillatory rhythms: a single-case longitudinal study

Abstract

We provide direct electrophysiological evidence that mirror therapy (MT) can change brain activity and aid in the recovery of motor function after stroke. In this longitudinal single-case study, the subject was a 58-yr-old man with right-hand hemiplegia due to ischemic stroke. Over a 9-mo period we treated him with MT twice a week and measured electroencephalograms (EEG) before, during, and after each therapy session. Using advanced signal processing methods, we identified five distinct movement-related oscillatory EEG components: one slow component designated as mu rhythm and four faster components designated as sensorimotor rhythms. Results show that MT produced long-term changes of two oscillatory EEG components including the mu rhythm, which is a well-documented correlate of voluntary movement in the frequency range of 7.5–12 Hz. Specifically, MT was significantly associated with an increase in the power of mu rhythm recorded over both hemispheres and a decrease in the power of one sensorimotor component recorded over the affected hemisphere. To obtain robust, repeatable individual measures of EEG components suitable for longitudinal study, we used irregular-resampling autospectral analysis to separate fractal and oscillatory components in the EEG power spectrum and three-way parallel factor analysis to isolate oscillatory EEG components and track their activations over time. The rhythms were identified over individual days of MT training and were clearly related to the periods of event-related desynchronization and synchronization (rest, observe, and move) during MT. Our results are consistent with a model in which MT promotes recovery of motor function by altering neural activity associated with voluntary movement. NEW & NOTEWORTHY We provide novel evidence that mirror therapy (MT), which helps in the recovery of motor function after a stroke, is also associated with long-lasting changes in brain electrical activity. Using precise measurements of oscillatory EEG components over a 9-mo period in a victim of ischemic stroke, we showed that MT produced long-term increases in the mu rhythm recorded over both hemispheres and a decrease in a sensorimotor EEG component recorded over the affected hemisphere.