Investigation of cross-frequency phase-amplitude coupling in visuomotor networks using magnetoencephalography.

Cross-frequency phase-amplitude coupling (PAC) within large neuronal populations is hypothesized to play a functional role in information processing in a range of cognitive tasks. The goal of our study was to examine the putative role of PAC in the brain networks that mediate continuous visuomotor control. We estimated the cortical activity that mediates visuomotor control via magnetoencephalography (MEG) recordings in 15 healthy volunteers. We extracted the cortical signal amplitudes and phases at the frequencies of interest by means of band-pass filtering followed by Hilbert transforms. To quantify task-related changes of PAC, we implemented a technique based on the Kullback-Leibler divergence. The choice of this technique among others was based on the results of comparisons performed on simulations of coupled sources in various noise conditions. The application of PAC to the MEG data revealed a significant task-related increase in coupling between the phase of delta (2-5 Hz) and the amplitude of high-gamma (60-90 Hz) oscillations in the occipital and parietal cortices as well as in the cerebellum. Remarkably, when comparing PAC in the early trials to PAC recorded towards the end of the experiment we found a significant increase in delta-high-gamma coupling over time in the superior parietal lobule, possibly reflecting visuomotor adaptation processes. Our results suggest that, in addition to power modulations, cross-frequency interactions play a key role in visuomotor behavior.