Neural Correlates of the DMT Experience Assessed with Multivariate EEG

Neural correlates of the DMT experience assessed with multivariate EEG Studying transitions in and out of the altered state of consciousness caused by intravenous (IV) N,N-Dimethyltryptamine (DMT - a fast-acting tryptamine psychedelic) offers a safe and powerful means of advancing knowledge on the neurobiology of conscious states. Here we sought to investigate the effects of IV DMT on the power spectrum and signal diversity of human brain activity (6 female, 7 male) recorded via multivariate EEG, and plot relationships between subjective experience, brain activity and drug plasma concentrations across time. Compared with placebo, DMT markedly reduced oscillatory power in the alpha and beta bands and robustly increased spontaneous signal diversity. Time-referenced and neurophenomenological analyses revealed close relationships between changes in various aspects of subjective experience and changes in brain activity. Importantly, the emergence of oscillatory activity within the delta and theta frequency bands was found to correlate with the peak of the experience - particularly its eyes-closed visual component. These findings highlight marked changes in oscillatory activity and signal diversity with DMT that parallel broad and specific components of the subjective experience, thus advancing our understanding of the neurobiological underpinnings of immersive states of consciousness. Introduction N, N, Dimethyltryptamine (DMT) is a naturally-occurring serotonergic psychedelic capable of producing experiences that, in intensity, surpass those associated with standard doses of most orally administered psychedelics and indeed most other categories of psychoactive drugs. The subjective effects of intravenous DMT have a rapid onset and are characterized by unusually vivid visual imagery and somatic effects, which arise within seconds of the injection. At high doses, the experience rapidly progresses into a deep and profound immersion - sometimes described as a ‘breakthrough’. This experience is often characterized by a sense of entering into an entirely ‘other’ but no less ‘real’ world or dimension. It is not uncommon for people to describe encounters with sentient ‘entities’ or ‘presences’ within this perceived other world and for the experience to subsequently challenge beliefs about the nature of reality and consciousness. The phenomenology of the DMT experience suggests it may be an especially powerful scientific tool for illuminating the neurobiology of consciousness. DMT experiences can be said to resemble ‘world-analogue’ experiences (i.e. interior analogues of external worlds) – similar to the dream state. It is logical to presume that conscious processing becomes ‘functionally deafferented’ (i.e. cut-off) from the external sensorium in these states, paralleled by what is presumably an entirely internally generated ‘simulation state’, felt as entry into an entirely other world. The rapid, short-acting and dramatic subjective effects of intravenous DMT therefore render it well-suited for investigating the neurobiology of consciousness with functional brain imaging – and this is what we sought to exploit here. Previous EEG and magnetoencephalography (MEG) studies of psychedelic-induced changes in brain activity have yielded generally consistent results. While broadband decreases in (absolute) oscillatory power have been seen with psilocybin, LSD, and (the DMT-containing ceremonial brew) ayahuasca, some evidence suggest that these reductions are more pronounced in certain frequency bands, e.g. suppression of alpha power is perhaps the most robust and reliable functional brain effect of psychedelics. Supplementing traditional frequency-based analyses, another reliable finding is increased complexity, diversity, or entropy of brain activity under psychedelics – an intriguing result given that related measures are known to reliably index a range of different conscious states. Recent advances in analytical methods have enabled the decomposition of spectral power into its oscillatory and fractal (1/f) components and these components are thought to have distinct functional relevancies. Importantly, oscillatory activity has been linked to specific generative mechanisms. For example, alpha power has been sourced to thalamic and visual cortical generators and a top-down suppressive function, while theta power has been associated with limbic generators and learning. Conversely, the origin and functional relevance of 1/f activity is poorly understood. Psychedelics have, however, been found to affect 1/f-related activity – and this has also been seen in other atypical states of consciousness. For these reasons, we assessed the effects DMT on rhythmic and fractal activity both separately and in combination in order to examine whether they are differently affected by DMT and how such changes relate to the different aspects of the DMT experience. EEG was chosen as a preferred brain imaging modality (i.e. over fMRI) due to its high temporal resolution, related ability to capture the fast-acting effects of DMT, and the known effects of psychedelics on vascular activity - which may be confounded with neuronal activity when using functional Magnetic Resonance Imaging; fMRI. The primary aim of our study was to determine how a bolus intravenous injection of DMT (versus a bolus intravenous injection of saline) affects the power spectrum and signal diversity of EEG recorded brain activity. Further, we aimed to establish the relationship between these brain activity measures, the real-time progression of the subjective experience and parallel changes in plasma levels of DMT. Finally, both conventional psychometric analyses and more temporally finessed methods - inspired by neurophenomenology - were utilized to assist the process of mapping between brain and experience. Subjective reports were obtained both via questionnaires and micro-phenomenological interviews, which promote detailed chronological accounts of subjective experiences, while reducing biases commonly associated with first person reports - making this technique ideal for neurophenomenological analyses. Our primary hypothesis was that DMT would decrease oscillatory power in the alpha band and increase cortical signal diversity and that these effects would correlate with changes in conscious experience across time. Results Subjective effects Participants were asked to provide ratings of the subjective intensity of the drug effects at every minute for a total of 20 minutes after DMT and placebo administration. Figure 1A displays the group-averaged intensity plots for each minute for a total of 20 minutes post-injection. Paired T-tests revealed that the subjective intensity of the experience remained significantly higher under DMT vs placebo for 17 minutes post-dosing (False Discovery Rate - FDR corrected) and peak subjective effects occurred 2–3 minutes post-injection. Supplementing these basic intensity ratings, participants were asked to rate different aspects of their experiences using various visual analogue scales (VAS). All items were rated significantly higher in the DMT condition compared with placebo (FDR corrected) (Fig. 1B). Ratings were given retrospectively, at ~30 minutes following administration, i.e. once the acute effects of DMT had sufficiently subsided. Time-averaged EEG results Averaged EEG from the first 5 minutes of resting state activity following administration of DMT was contrasted against the same period after placebo, focusing on changes in the power spectrum and spontaneous signal diversity (LZs and LZsN). One participant was excluded due to excessive movement artifacts following DMT. Supporting one aspect of our primary hypothesis, contrasts revealed spatially-widespread and statistically-marked decreases in the alpha band (max. t(11) = −3.87, cluster p = 5.33e-04) and more modest decreases in the beta band (max. t(11) = −3.30, cluster p = 0.033) under DMT (Fig. 2A). Decomposing the EEG spectra into its oscillatory and fractal (1/f) components revealed consistent changes in oscillatory power as reported above (alpha: max. t(11) = −3.87, cluster p = 2.67e-04. Beta: max. t(11) = −3.11, cluster p = 0.04), while the fractal component showed significantly reduced power within all frequency bands < 30 Hz (delta: max. t(11) = −3.91, cluster p = 0.024. Theta: max. t(11) = −4.28, cluster p = 0.007. Alpha: max. t(11) = −3.67, cluster p = 0.014. Beta: max. t(11) = −3.48, cluster p = 0.02) (Fig. 2A and see Fig. S1 for detailed results for DMT and placebo separately). Signal diversity, as measured by Lempel-Ziv complexity (LZs) and normalized Lempel-Ziv complexity (LZsN), was significantly increased under DMT relative to placebo (max. t(11) = 8.09, cluster p = 2.67e-04; max. t(11) = 4.26, cluster p = 0.0029), respectively (Fig. 2C) – consistent with our primary hypothesis. Results also revealed the emergence of prominent theta oscillations under DMT, to the extent that this rhythm replaced alpha as the peak frequency in terms of power (within the 4–45 Hz range: mean = 7.36 Hz, SEM = 0.68). This emergent theta rhythm under DMT was more evident in the oscillatory power spectrum, i.e. once the fractal component had been removed. As expected, an alpha peak was maintained throughout the placebo session (mean = 9.28 Hz, SEM = 0.62) (t(11) = −2.52, p = 0.029) (Fig. 2B). Time-sensitive EEG results In addition to consistent alpha and beta reductions, minute-by-minute analyses revealed decreases in delta and theta bands only for the first minute post DMT injection – after which recovery (and increases in theta for the oscillatory component) were identified at minutes 2–3. These results indicate that DMT induces a general decrease in total power across all frequency bands between 1 and 30 Hz; however, there is a transient normalization/increases in theta and delta frequencies at the time of peak subjective intensity, which is especially evident in the oscillatory component of the signal. The spontaneous signal diversity measure, LZs, was found to be consistently increased for the whole of the post-injection period - and increases in LZsN were evident from the time of peak intensity onwards (Fig. S2). Subjective vs EEG effects across time In order to assess the relationship between the subjective and EEG changes across time, data was segmented into one-minute blocks. Results revealed a negative correlation between changes in total alpha power under DMT and ratings of subjective intensity that was significant for all recorded channels (max. t(11) = −16.05, cluster p = 2.67e-04; white dots, Fig. 3A). Decreased beta power similarly correlated with higher intensity ratings (max. t(11) = −9.83, cluster p = 0.0043). Analysis performed on just the oscillatory component of the signal showed mostly consistent results (alpha: max. t(11) = −14.85, cluster p = 2.67e-04. Beta: max. t(11) = −11.08, cluster p = 0.004), although additional positive correlations between intensity and delta (max. t(11) = 4.68, cluster p = 0.007) and theta power (max. t(11) = 7.17, cluster p = 0.003) also emerged as statistically significant (black dots, Fig. 3A). Fractal power revealed a negative correlation between (higher) intensity ratings and (reduced) theta (max. t(11) = −3.13, cluster p = 0.04), alpha (max. t(11) = −3.12, cluster p = 0.047) and beta power (max. t(11) = −5.21, cluster p = 0.01). These results reveal the emergence of a functionally relevant rhythmicity within the delta and theta frequency bands under DMT that was not evident in total power, which includes the fractal component of the signal. In fact, within the theta band, the fractal component appears to behave in an opposite way to the oscillatory component under DMT, i.e. there is increased theta power in the oscillatory component but decreased theta in the fractal component. Supporting our primary hypothesis, increased signal diversity (LZs) under DMT correlated positively with subjective intensity ratings in posterior and central channels (max. t(11) = 9.96, cluster p = 2.67e-04). After controlling for changes in spectral power (LZsN), the relationship between signal diversity and intensity remained positive in the posterior channels only (max. t(11) = 5.11, cluster p = 0.009). Plasma DMT vs EEG effects Here we assessed the relationship between changes in the EEG data (frequency bands and signal diversity) and plasma concentrations of DMT across time. In a similar manner to the subjective values, higher concentrations of DMT in the blood were associated with greater reductions in alpha (max. t(11) = −23.59, cluster p = 2.67e-04) and beta power (max. t(11) = −12.61, cluster p = 0.04). Similar effects were seen when analyses were performed on the oscillatory component of the signal (alpha: max. t(11) = −28.32, cluster p = 2.67e-04. Beta: max. t(11) = −20.62, cluster p = 0.022), while the fractal component showed negative correlation between (higher) plasma concentrations and (reduced) theta power (max. t(11) = −4.11, cluster p = 0.038). As predicted, a relationship was also evident between plasma DMT and increased signal diversity (LZs: max. t(11) = 25.61, cluster p = 2.67e-04 and LZs normalized: max. t(11) = 7.63, cluster p = 2.67e-04) (Fig. 4). Neurophenomenology Micro-phenomenological interviews (MPIs) were performed post-hoc to discover distinct (core) components of the subjective experience – that could then be used to constrain participant ratings referenced to specific time points, i.e. each passing minute. Three major common dimensions were found across participants, i.e.: (1) visual, (2) bodily and (3) emotional/metacognitive experiences. These dimensions were extracted from each of the participants’ interviews and then rated by a researcher not involved in EEG analysis with reference to each passing minute within the 20-minute recording period (see Methods for details) (Fig. 5A). Adopting a data-led approach, we chose to look at components of the EEG that had already shown interesting relationships with intensity ratings, namely: alpha, beta, delta and theta power, plus signal diversity measures (LZs and LZsN). Results revealed a negative correlation between changes in visual intensity and changes in total alpha (max. t(11) = −14.24, cluster p = 2.67e-04) and beta (max. t(11) = −6.17, cluster p = 0.04) power as well as a positive relationship with changes in delta (max. t(11) = 6.06, cluster p = 0.004) and theta (max. t(11) = 6.59, cluster p = 0.01) power - when just the oscillatory component of the signal was used for analyses. Similar positive relationships between intensity ratings and EEG measures were seen for LZ (i.e. LZs: max. t(11) = 16.74, cluster p = 2.67e-04 and LZsN: max. t(11) = 6.62, cluster p = 0.008). Ratings of bodily effects were negatively correlated with changes in the beta band (max. t(11) = 3.17, cluster p = 0.0496) only. Lastly changes in the emotional/metacognitive dimension [Full text truncated at 15000 characters. The complete article is available from the publisher at the DOI above.] Source and licence Timmermann C, et al. (2019). Neural Correlates of the DMT Experience Assessed with Multivariate EEG. Scientific Reports. https://doi.org/10.1038/s41598-019-51974-4 PubMed Central PMC6864083. Distributed under CC BY, https://creativecommons.org/licenses/by/4.0/ . Reproduced on dmtcode.com under that licence. Changes made: full text extracted from the PubMed Central BioC service, reference list, figures, tables and funding statements removed. No wording was altered. Retrieved 2026-08-21.