Corticomuscular coherence in acute and chronic stroke

Question: After stroke a profound neuronal reorganization occurs and new, previously not engaged areas can be recruited in motor activities. However, not all post-stroke neuronal changes contribute directly to motor recovery by re-establishing fine motor control. Corticomuscular coherence (CMC) is a measure which allows tracing neuronal reorganizations that are functionally relevant for motor recovery. Previous CMC studies were performed only in chronic stroke stage when many compensatory processes already took place. In order to study the development of compensatory changes, we aimed at studying CMC in patients both at the acute and chronic stages of stroke.

Methods: We studied eleven hemiparetic patients with cortical or subcortical stroke. They performed isometric contractions with the affected and unaffected hand while multichannel EEG and EMG were recorded. For the detection of CMC we used our recently developed method Regression-CMC – an algorithm optimized for detecting corticomuscular interactions.

Results: In acute stroke (within five days post-stroke), the CMC amplitudes on the unaffected side were larger compared to the affected side and also larger compared to the unaffected side in the chronic period six months after stroke. Moreover, in the acute period, the CMC peak frequencies were decreased on both sides while they increased to normal range in chronic stage and did not show any difference compared to control subjects. In addition, in chronic stage, there were no inter-hemispheric or group differences in CMC amplitude.

Conclusions: As all patients in the present group showed very good motor recovery, the modulation of CMC amplitude and frequency over time might reflect the process of motor recovery. We hypothesize that the CMC changes might relate to a decrease of cortical inhibition from acute to chronic stroke stage.