Time-to-onset and temporal dynamics of EEG during breath-watching meditation

Mindfulness practices, including meditation, have gained immense popularity as mind-body interventions for improving mental well-being. A vast body of research consistently demonstrates the positive effects of meditation on brain function and psychological well-being, often highlighting changes in alpha and theta brainwave frequencies. However, a critical gap exists in our understanding of the temporal dynamics of these changes – specifically, when these changes begin and when they peak during a meditation session. This study aims to address this gap by examining the time-to-onset and temporal dynamics of EEG activity during breath-watching meditation across different experience levels. The research focuses on breath-watching, a focused-attention meditation technique, examining three groups: meditation-naive controls, novice meditators, and advanced meditators trained in the Isha Yoga tradition. The study leverages high-density EEG data with excellent temporal resolution to track changes in brain oscillations across various frequency bands throughout the meditation practice. This dynamic approach allows for a more nuanced understanding of the brain's response to meditation compared to previous studies that predominantly relied on averaged data from epochs of meditation.

Existing neuroscientific literature consistently shows increased alpha and theta power in both the resting state (trait effect) and during meditation (state effect). Changes in other frequency bands, such as gamma, are often reported only among experienced practitioners. Meditators typically experience a state of 'relaxed alertness,' reflected in EEG data by increased power in both low and high-frequency bands. However, past research often treated the brain during meditation as a static entity, analyzing short, averaged EEG epochs, neglecting the critical aspects of time-to-onset and the intricate temporal dynamics of brain oscillation changes. This study departs from these traditional approaches by focusing on the dynamic changes in brain activity throughout the meditation session to pinpoint the exact time-to-onset of neurophysiological changes and the time at which these effects peak, thus adding to our understanding of the dynamic interplay of brain oscillations during meditation.

This study analyzed previously published EEG data recorded using a 128-channel high-density EEG system. Three groups of participants were included: meditation-naïve controls (n=28), novice meditators (n=33), and advanced meditators (n=42), all aged 25-50, healthy, and fluent in English. Meditators were trained in the Isha Yoga tradition, with novice and advanced groups defined based on their participation in a specific Isha Yoga program. The EEG data were collected during a breath-watching meditation session as part of a larger experimental paradigm. EEG preprocessing involved resampling, average referencing, band-pass filtering (0.5-40 Hz), artifact rejection using Artifact Subspace Reconstruction (ASR) and Independent Component Analysis (ICA) for noise reduction. Power spectral densities (PSD) were calculated for standard frequency bands (delta, theta, theta-alpha, alpha, beta1, beta2, gamma1). The first 30 seconds of breath-watching served as the baseline. Within-group comparisons assessed power differences between the baseline and successive 1-minute segments (non-overlapping windows). Between-group comparisons assessed power differences at 0.5, 3, 6, and 9 minutes. Statistical analyses used the LIMO toolbox with robust t-statistics and cluster-based correction for multiple comparisons. Statistical significance was set at p<0.05.

Within-group analyses revealed a consistent time-to-onset of neurophysiological effects around 2-3 minutes after the start of meditation across all three groups. This included significant increases in theta, alpha, and beta1 power, and significant decreases in delta and gamma1 power. These effects peaked between 7 and 10 minutes. Between-group comparisons showed that advanced meditators exhibited significantly higher theta and theta-alpha power at all time points compared to the other two groups. They also showed significantly lower delta power at 0.5 and 3 minutes compared to controls and lower gamma power than controls at 9 minutes. Notably, while the time-to-onset and peak effects were similar across groups, the magnitude of the changes differed significantly between the advanced meditators and the other two groups. Table 2 summarizes the temporal and power dynamics of EEG effects across frequency bands and groups during breath-watching meditation. Figures 1-4 illustrate these dynamics through visual representations, including power spectral density plots and topographical maps highlighting electrodes with significant differences.

The findings of this study provide novel insights into the temporal dynamics of EEG changes during breath-watching meditation. The consistent observation of neurophysiological changes beginning around 2-3 minutes across all experience levels suggests a relatively rapid onset of meditative effects. The peaking of these effects between 7-10 minutes highlights the importance of sufficient meditation duration. The differences in magnitude of these changes between the groups, particularly the higher theta power and lower delta and gamma power in advanced meditators, point towards the impact of experience and expertise on the depth and quality of the meditative state. These findings support existing research showing that advanced meditators experience greater synchronization of neural oscillations, potentially reflecting enhanced attentional focus and meta-awareness. This suggests that longer-term meditation practice leads to more profound neurophysiological changes, though the precise mechanisms are still being explored. The study supports the notion that even brief meditation practices could offer significant benefits to mental well-being, making it an accessible and scalable intervention.

This study provides valuable insights into the temporal dynamics of EEG changes during breath-watching meditation, demonstrating that neurophysiological changes begin around 2-3 minutes and peak around 7-10 minutes across all experience levels. The magnitude of these changes is significantly greater in advanced meditators, highlighting the role of practice. These findings support the implementation of brief, accessible meditation practices for enhancing mental well-being, particularly in light of the global rise in mental health challenges.

The study's limitations include the lack of phenomenological data on meditative depth and quality, and the absence of pre- and post-meditation mental well-being measures. These additions could have provided richer contextual information and stronger correlations between neurophysiological changes and subjective experiences. Future research should address these limitations to gain a more holistic understanding of the meditation experience.