Abstract
Our recent finding of a meditation-related increase in low-frequency NREM sleep EEG oscillatory activities peaking in the theta-alpha range (4-12 Hz) was not predicted. From a consolidated body of research on sleep homeostasis, we would expect a change peaking in slow wave activity (1-4 Hz) following an intense meditation session. Here we compared these changes in sleep with the post-meditation changes in waking rest scalp power to further characterize their functional significance. High-density EEG recordings were acquired from 27 long-term meditators (LTM) on three separate days at baseline and following two 8-hr sessions of either mindfulness or compassion-and-loving-kindness meditation. Thirty-one meditation-naïve participants (MNP) were recorded at the same time points. As a common effect of meditation practice, we found increases in low and fast waking EEG oscillations for LTM only, peaking at eight and 15 Hz respectively, over prefrontal, and left centro-parietal electrodes. Paralleling our previous findings in sleep, there was no significant difference between meditation styles in LTM as well as no difference between matched sessions in MNP. Meditation-related changes in wakefulness and NREM sleep were correlated across space and frequency. A significant correlation was found in the EEG low frequencies (<12 Hz). Since the peak of coupling was observed in the theta-alpha oscillatory range, sleep homeostatic response to meditation practice is not sufficient to explain our findings. Another likely phenomenon into play is a reverberation of meditation-related processes during subsequent sleep. Future studies should ascertain the interplay between these processes in promoting the beneficial effects of meditation practice.