The Balanced Mind and its Intrinsic Neural Timescales in Advanced Meditators

Equanimity is an even-minded state toward all experiences, regarded across traditions as a high mental state and a key outcome of meditation. Two core features are deidentification (distancing from internal thoughts and reduced duration of internal attention) and non-dual awareness (attenuated self–other and internal–external boundaries). Although questionnaires exist to quantify equanimity, objective neural markers are lacking. Intrinsic neural timescales (INTs), indexed by the autocorrelation window (ACW), provide a temporal measure of how long neural activity integrates information and may capture the temporal signature of equanimity. The study investigates whether advanced meditators show neural signatures consistent with deidentification (shorter ACW during internal attention to breath) and non-duality (reduced ACW differences between internal and external tasks), and whether these neural measures relate to psychological measures of equanimity, non-duality, and non-attachment.

Prior work distinguishes equanimity from mindfulness and implicates it as a predictor of well-being. Phenomenology describes deidentification and non-dual awareness as central to meditative expertise. EEG and neuroimaging studies of meditation report alterations in oscillatory power (e.g., theta, gamma) and functional connectivity, especially in advanced practitioners. However, no established neural measure directly indexes equanimity's temporal features. Neuroscience research reveals a cortical hierarchy of intrinsic neural timescales (INTs), with shorter timescales in unimodal regions (supporting temporal segregation) and longer timescales in transmodal regions (supporting temporal integration). ACW-50 quantifies the decay of autocorrelation and has been linked to perception, cognition, consciousness, and self-related processing. This framework suggests that shorter, more stable INTs during internal attention could reflect deidentification, while a balanced ACW across internal and external attention could reflect non-duality. The Isha Yoga literature reports benefits in stress, immunity, autonomic measures, and altered neural dynamics, with equanimity as a key cultivated quality.

Design: Cross-sectional EEG study comparing advanced meditators (ADV), novice meditators (NOV), and meditation-naïve controls (CNT) during internal (breath-watching) and external (visual oddball; ANGEL) attention tasks, plus rest and other sessions. Participants: N=103 healthy adults (ADV n=42; NOV n=33; CNT n=28), matched on demographics. ADV mean age 35.57 (SD 6.81) years; mean lifetime practice 5507.80 (SD 2897.44) hours. NOV mean age 31.66 (SD 7.64); lifetime practice 1637.24 (SD 1126.61) hours. CNT mean age 31.14 (SD 6.38), no meditation experience. Ethics approval from NIMHANS; informed consent obtained. Procedure: Four EEG sessions: (1) alternate nostril breathing pranayama, (2) breath watching (focused attention to natural breath), (3) cognitive task (ANGEL, a gamified visual oddball, ~15 min, 448 trials), and (4) Shoonya meditation or sit-still for controls. Each session had 4-minute rest periods (eyes open/closed alternating). Meditation depth was assessed after breath-watching and Shoonya. EEG acquisition: 128-channel Geodesic EEG System 300 (Philips Neuro); 1 kHz sampling, AFz ground, Cz reference; impedance <50 kΩ; stimuli via E-prime 2.0. Preprocessing: EEGLAB-based pipeline. Resample to 250 Hz; average reference; 0.5–80 Hz bandpass and 50 Hz notch; artifact subspace reconstruction (ASR, 5 SD); ICA (infomax) with ICLabel (90% threshold) to remove ocular/muscle/ECG components; spherical spline interpolation of bad channels. Mean data removed: ADV 11.19%, NOV 12.61%, CNT 11.21%. ACW computation: For each electrode, compute autocorrelation function on 10 s epochs with 1 s sliding; within each, average ACF from 1 s windows (50% overlap). ACW-50 identified as first lag where ACF decays to 50% of max. For each electrode, compute ACW mean (20% trimmed mean) and variance (median average deviation) across epochs. Aggregate analyses at scalp level and by regions; line plots across internal–external gradient, topoplots, and difference scores (Breath Watch minus Task). Psychometrics: MEDEQ (30 items; clusters include non-duality; n=70 completed), Equanimity assessed by MEDEQ item 2 (and expanded 4- and 8-item composites), NAS-7 (non-attachment), SPANE (positive, negative, and balance scores). Reliability: alpha 0.8–0.92. Statistics: Non-parametric tests (Kruskal–Wallis, Dunn, Mann–Whitney, chi-square); effect sizes with 95% CIs; p<0.05 threshold. Spearman correlations for associations between ACW metrics and psychometrics. Non-inferiority tests where appropriate. Mediation analyses (lavaan; bootstrap n=5000) tested whether non-duality mediates relationships of (a) lifetime meditation hours and equanimity, (b) NAS-7 and equanimity, and (c) ACW metrics and equanimity.

• Demographics: Groups matched on key sociodemographics.
• Psychological measures:
  • Meditation depth during breath-watching differed across groups: χ²_Kruskal–Wallis(2)=25.42, p=3.02e-06, η²_ordinal=0.37; ADV highest, then NOV, CNT lowest.
  • Non-duality differed across groups: χ²_Kruskal–Wallis(2)=22.94, p=1.04e-05, η²_ordinal=0.33; ADV>NOV>CNT.
  • Equanimity (MEDEQ item 2) during breath-watching differed: χ²_Pearson(4)=10.52, p=0.03, V_Cramér=0.22; high equanimity: ADV 92%, CNT 52% (22% low). Expanded 4- and 8-item equanimity composites also differed (supplement).
  • Non-attachment (NAS-7) differed: χ²_Kruskal–Wallis(2)=18.42, p=1.0e-04, ε²_ordinal=0.18; ADV highest.
  • Affect balance (SPANE-B) differed: χ²_Kruskal–Wallis(2)=11.98, p=2.51e-03, ε²_ordinal=0.12; ADV highest; ADV showed more positive and fewer negative affects (supplement).
  • Mediation: Non-duality fully mediated effects of lifetime meditation hours on equanimity: a path z=3.469, p=0.001; b path z=5.254, p=0.000; c' non-significant (z=1.659, p=0.097); indirect ab z=2.653, p=0.008. Non-duality also fully mediated NAS-7 → equanimity: a z=6.237, p=0.000; b z=5.363, p=0.000; c' z=0.926, p=0.354; ab z=3.685, p=0.000.
• Neural ACW (duration) findings:
  • Breath-watching (internal attention): ADV showed shorter ACW mean vs CNT: W=306.00, p=0.01, rank-biserial=-0.38 (large effect); and lower ACW variance: W=294.50, p=0.03, rank-biserial=-0.33. No group difference during external task (supplement).
  • Internal–external balance (non-duality index): Controls showed significant ACW mean difference between breath-watching and task: W=470.00, p=2.59e-05, rank-biserial=0.72; ADV showed no significant difference: W=770.50, p=0.06, rank-biserial=0.27 (non-inferiority supported). Topographies: CNT had widespread anterior differences; ADV had few electrodes differing. Difference score (BW−Task) ACW mean differed CNT vs ADV: W=209.00, p=0.02, rank-biserial=-0.38.
  • Rest vs breath-watching: CNT differed (Rest EC vs BW) ACW mean W=535.00, p=3.16e-03, rank-biserial=0.47; ADV showed no difference W=735.00, p=0.90, rank-biserial=0.02. Similar for variance.
• Neural–psychological associations:
  • ACW during breath-watching correlated negatively with meditation depth: mean ρ_S=-0.24, p=0.0473; variance ρ_S=-0.30, p=0.0149.
  • ACW during breath-watching correlated negatively with non-duality: mean ρ_S=-0.28, p=0.0211; variance ρ_S=-0.30, p=0.0177.
  • ACW BW−Task difference score correlated negatively with meditation depth ρ_S=-0.29, p=0.0331 and with non-duality ρ_S=-0.31, p=0.0227.
  • ACW correlated negatively with equanimity (item 2): BW mean ρ_S=-0.35, p=0.0043; BW variance ρ_S=-0.38, p=0.0019; BW−Task mean ρ_S=-0.37, p=0.0074; BW−Task variance ρ_S=-0.43, p=0.0136 (supplement). Expanded 4- and 8-item equanimity correlations also negative (supplement).
  • Mediation: Non-duality mediated ACW → equanimity relationships. For BW−Task ACW mean to equanimity: a z=-2.166, p=0.030; b z=4.807, p=0.000; c' z=-1.451, p=0.147; indirect a*b z=-1.975, p=0.048. For BW ACW variance to equanimity: significant indirect effect (p=0.015).

Findings support the hypothesis that equanimity in advanced meditators has identifiable temporal neural signatures. Shorter and more stable ACW during internal attention (breath-watching) aligns with deidentification: reduced duration of internal attention to thoughts and diminished automatic reactivity. The absence of significant ACW differences between internal and external tasks in advanced meditators indicates a balanced, non-dual mode of processing, unlike controls who show marked internal–external ACW divergence. Neural measures related systematically to psychological measures of meditation depth, non-duality, and equanimity, and non-duality mediated both behavioral (lifetime practice, non-attachment) and neural (ACW metrics) pathways to equanimity. These results connect phenomenology of equanimity to objective neural timescale dynamics, suggesting that shorter, more stable intrinsic timescales and a flatter internal–external ACW gradient are central to the neural instantiation of equanimity. The work advances an objective framework for equanimity, with implications for meditation science and mental health interventions targeting resilience and balanced affect.

The study introduces ACW-based intrinsic neural timescales as objective indices of equanimity. Advanced meditators exhibited (1) higher state and trait equanimity, (2) shorter and more stable neural timescales during breath-focused internal attention (neural index of deidentification), and (3) minimal ACW differences between internal and external tasks (neural index of non-duality). ACW metrics correlated negatively with meditation depth, non-duality, and equanimity, with non-duality mediating ACW–equanimity relationships. These findings suggest shorter and more stable neural duration as a key neural marker of equanimity. Future work should incorporate task designs probing stress/emotion and include direct psychological measures of duration in external tasks, assess longitudinal training effects, and examine generalization across meditation traditions and clinical populations.

• The inference of a non-dual state during external tasks is based on ACW patterns; no direct psychological measure of experiential duration or non-duality was collected concurrently during the external task.
• The study did not test equanimity under stress- or emotion-eliciting conditions; responsiveness of neural indices of equanimity to such perturbations remains unknown.
• Cross-sectional design limits causal inference about meditation training effects; potential selection effects cannot be excluded.
• MEDEQ was administered to a subset (n=70), which may reduce power for some analyses; some correlations have modest effect sizes.