The time course of functional coupling between human cortical motor areas during internally driven vs. externally cued movements

The functional coupling between the primary motor cortex (M1) and the supplementary motor area (SMA) in the generation of internally paced versus externally cued rhythmic movements was explored using electroencephalography (EEG). This has important implications for the study of Parkinsonian patients who demonstrate decreased ability to perform internally paced rhythmic movement tasks. In particular, the temporal evolution of the coherence between M1 and SMA was studied using a recently developed time-frequency wavelet coherence algorithm. As this approach is not reliant upon pooling data from multiple trials to form a single estimate of the coherence for each subject, a subject by subject comparison is possible to determine subject specific frequencies of interest. It was found that at certain frequencies, the coupling between M1 and SMA was increased in the internally paced versus the externally triggered movement task. At only these specific frequencies did the peak of the coherence in the internal task precede that of the peak in the external task, which was time locked with the movement onset. This suggests a dual role of the M1-SMA coupling for both movement preparation and movement execution.