DMT-induced shifts in criticality correlate with self-dissolution

The authors frame their study within recent interest in how classic psychedelics alter subjective experience and brain dynamics. They explain the concept of criticality — a dynamical regime in which correlations persist over long distances and timescales, producing scale-invariant, complex fluctuations — and note that the human brain is often thought to operate near criticality. Long-range temporal correlations (LRTCs) in oscillatory amplitude envelopes are presented as an empirical signature of proximity to criticality, and detrended fluctuation analysis (DFA) is introduced as a method for quantifying LRTCs. The introduction also notes that DFA alone cannot distinguish shifts toward inhibition-dominated (subcritical) versus excitation-dominated (supercritical) regimes, and that a recently developed functional excitatory/inhibitory (fE/I) ratio can provide directional information. This study set out to quantify markers of criticality in human EEG recordings under the influence of the short-acting psychedelic DMT, and to relate those markers to subjective reports of self-dissolution (measured with a specific visual analogue scale item). M. and colleagues combined two placebo-controlled, single-blind, within-participant EEG datasets to test whether DMT alters DFA-estimated LRTCs and fE/I, whether those changes indicate sub- or supercritical shifts, and whether such changes correlate with disruption of self-related processing during the psychedelic state. The authors emphasise that linking criticality metrics with subjective self-dissolution could provide novel neural correlates of self-related processing in altered states of consciousness.

M. and colleagues combined EEG data from two within-participant, single-blind, placebo-controlled studies to produce a final sample of 27 healthy adults (12 female; mean age 34.1, SD 8.7) after exclusion of recordings with excessive artefacts. Participants were screened for physical and mental health and excluded for underage status, MR contraindications, lack of prior psychedelic experience, prior adverse psychedelic reactions, psychiatric or physical illness rendering them unsuitable, family history of psychosis, or excessive substance use. Ethics approval and regulatory oversight were obtained and all participants gave written consent. Study 1 contributed 12 participants and was a dose-finding design in which participants received placebo on a first visit and DMT on a second visit one week later; administered DMT fumarate doses varied across participants (reported doses: 7 mg, 14 mg, 18 mg, 20 mg). Study 2 contributed 15 participants who received 20 mg DMT fumarate and placebo in counterbalanced order with visits two weeks apart. When participants took part in both studies only recordings from the second study participation were used to improve dose homogeneity. EEG was recorded at baseline and for 20 minutes after intravenous DMT administration (the bolus given over 30 seconds followed by a 15-second saline flush). After sessions, participants completed questionnaires and visual analogue scales (VAS) about their subjective experience. EEG acquisition used 31 scalp electrodes (10-20 system) with an MR-compatible BrainAmp MR amplifier; FCz served as reference and AFz as ground, and an ECG channel recorded heart rate. Preprocessing included visual inspection, removal of segments contaminated by muscle and movement artefacts, and cleaning with Independent Component Analysis. For LRTC estimation the authors bandpass-filtered signals, extracted amplitude envelopes (Hilbert transform), then applied detrended fluctuation analysis (DFA). DFA estimates the slope of root-mean-square fluctuations of the integrated, detrended amplitude envelope across window sizes; a DFA exponent near 0.5 indicates uncorrelated (white-noise-like) dynamics, while values approaching 1 indicate long-range temporal correlations consistent with proximity to criticality. DFA was calculated in specified time-scale ranges (e.g. 2–30 s for alpha). To infer the direction of criticality shifts, the authors used the fE/I algorithm, which estimates a functional excitatory/inhibitory ratio from the windowed covariation between amplitude and short-window estimates of temporal autocorrelation structure (a normalized fluctuation function proxy for DFA). The fE/I computation pipeline included bandpass filtering, Hilbert-derived amplitude envelopes, segmentation into overlapping 5-second windows with 80% overlap, normalization and detrending, computation of windowed normalized fluctuation functions, and finally deriving fE/I as 1 minus the Pearson correlation between windowed normalized fluctuations and windowed amplitudes. The fE/I value was only computed when the DFA exponent exceeded a threshold of 0.6, since far-from-critical signals lack the covariation necessary for reliable fE/I estimation. Statistical analyses were performed per channel with nondirectional paired t-tests (alpha p < 0.05) comparing placebo and DMT conditions; average DFA across statistically significant electrodes was reported. Changes in DFA and fE/I were calculated as differences between placebo and DMT to avoid order effects. Correlations between criticality metrics and subjective experience used change scores from DMT baseline to post-injection DMT and Pearson's correlation. Multiple comparisons across electrodes within a frequency band were controlled using the Benjamini–Hochberg false discovery rate with adjusted q-values < 0.10.

DFA (LRTC) changes: Paired-sample comparisons between placebo and DMT showed significant reductions in DFA exponents in theta, alpha and beta frequency bands. Reported group mean differences were ΔDFA = -0.06 for theta (p < .0001), ΔDFA = -0.09 for alpha (p < .0001), and ΔDFA = -0.06 for beta (p = .0004). These reductions were described as widespread across the scalp and robust across subjects according to the authors' electrode-wise tests and subject-level boxplots. The authors interpret reduced DFA exponents in the 0.5–1 range as reflecting a shift from more complex, less entropic (pink-noise-like) dynamics toward less complex, more entropic (white-noise-like) dynamics in alpha and adjacent bands under DMT. fE/I (directionality) changes: To determine the direction of the criticality shifts, the authors computed fE/I where DFA exceeded the threshold for reliable estimation. Compared with placebo, DMT produced a significant decrease in fE/I in the alpha band (ΔfE/I = -0.18; p = .0003), with effects most pronounced over parietal and occipital electrodes. In the beta band a significant reduction in fE/I was reported only in the left occipital region (ΔfE/I = -0.14; p = .0005). The authors summarise these results as evidence that the observed decreases in DFA in alpha and neighbouring bands reflect shifts toward subcritical (inhibition-dominated) regimes. Correlations with subjective experience: The authors tested correlations between criticality shifts and selected VAS items related to disruptions of self-related processing. They found statistically significant negative correlations between DFA reductions and ratings of self-dissolution (VAS item: "I experienced a disintegration of my sense of self or ego"): theta band DFA change correlated with self-dissolution r(25) = -0.61, p = .001, and alpha band DFA change correlated with self-dissolution r(25) = -0.56, p = .005. These correlations were reported as significant across many electrodes. The authors therefore report that the magnitude of the DMT-induced reduction in LRTCs in theta and alpha bands relates to the intensity of subjective self-dissolution. Additional notes reported by the authors: The authors emphasise that DFA reductions are distinct from reductions in oscillatory power and represent novel evidence of altered temporal structure (entropy and complexity) rather than merely amplitude changes. They also note that fE/I reductions and DFA changes were localised mainly to posterior regions for alpha and left occipital for beta where reported.

M. and colleagues interpret their findings as showing that DMT reduces long-range temporal correlations and shifts brain oscillations in alpha and neighbouring frequency bands toward a more entropic, less complex, and subcritical regime. They highlight three core observations: DMT caused statistically significant reductions in DFA in theta, alpha and beta bands; fE/I results indicate these shifts are in the subcritical direction particularly for posterior alpha; and the magnitude of DFA reductions in theta and alpha correlated with subjective ratings of self-dissolution. The authors propose that weakened LRTCs in alpha and adjacent bands may index disruption of the temporal continuity of self-referential processing, linking a measurable neural dynamic to the phenomenology of self-dissolution. The discussion situates the results relative to prior literature. The authors note that prior psychedelic studies have reported increases in entropy and reductions in alpha power and default-mode network connectivity; their findings are consistent with entropy increases but differ from some formulations of the entropic brain hypothesis that predict movement toward criticality. They suggest this discrepancy can reflect system-specific relationships between entropy and criticality: in their data reduced DFA (closer to white-noise-like dynamics) accompanies increased entropy and reduced complexity. The authors also compare their findings to reports of reduced LRTCs in anaesthesia and deep meditation, proposing that despite phenomenological differences (e.g. richness of experience in psychedelics versus paucity in anaesthesia), these states may share disruption of coherent, temporally extended self-referential processing, which could be captured by LRTC metrics. Mechanistic and frequency-specific interpretations are discussed. The authors highlight alpha oscillations' putative role in top-down predictive processes and note that alpha suppression and DMN dysregulation under psychedelics have been linked to experiential effects. They acknowledge that alpha activity also reflects low-level sensory processes and that intense visual content during DMT may interact with posterior alpha dynamics. The authors speculate that richness of phenomenal content under psychedelics may be indexed by higher-frequency activity (high gamma > 40 Hz), which was not accessible in their dataset, and suggest that different frequency bands may show opposing criticality shifts, motivating future time-resolved, frequency-specific analyses that align subjective reports with neural moments. Methodological caveats and limitations acknowledged by the authors include the inherent difficulty of proving that a real-world system is strictly at criticality (their measures test for consistent signatures), constraints of EEG in accessing high-frequency components, and the potential ambiguity in questionnaire items since participants were not asked to clarify how they understood particular items. They defend the use of DFA as robust to nonstationarities and appropriate for assessing LRTCs. The authors conclude that their results provide novel, frequency-dependent evidence on how DMT alters criticality, entropy and complexity of brain oscillations and that weak, subcritical LRTCs in alpha and adjacent bands may be a candidate neural correlate of disrupted self-related processing across several altered states of consciousness.