Neural correlates of the DMT experience assessed via multivariate EEG

This placebo-controlled EEG study (n=13) found that DMT reduces (oscillatory power) activity in the alpha and beta bands and increases them (especially at the peak) in the delta and theta bands.

Abstract of Neural correlates of the DMT experience assessed via 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.”

Authors: Christopher Timmermann, Leor Roseman, Michael Schartner, Raphael Milliere, Luke T. J. Williams, David Erritzoe, Suresh Muthukumaraswamy, Michael Ashton, Adam Bendrioua, Okdeep Kaur, Samuel Turton, Matthew M. Nour, Camilla M. Day, Robert Leech, David J. Nutt & Robin L. Carhart-Harris

Notes on Neural correlates of the DMT experience assessed via multivariate EEG

• First placebo-controlled study with DMT on brain activity
• DMT lowered oscillatory power in alpha and beta bands
• DMT increased oscillatory activity in delta and theta bands
• DMT increased spontaneous signal diversity

“The primary aim of our study was to determine the effects of a bolus intravenous injection of DMT (versus a bolus intravenous injection of saline) on 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.“

“In addition to consistent alpha and beta reductions, minute-by- minute analysis of the previous results revealed decreases in delta and theta bands for the first minute only – after which recovery (and increases in theta for the oscillatory component) were identified at minutes 2-3 post DMT injection. 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 (Figure S2).”

“One particularly consistent finding in neuroimaging research with psychedelics is decreased alpha power. Alpha is the most prominent rhythm of the resting-brain, particularly in humans, and particularly in adulthood. Alpha power has been linked with high-level psychological functioning, top-down predictive processing and related feedback connectivity – all of which have been found to be disrupted under serotonergic psychedelics.”

It seems that psychedelics (DMT) shut down a part of the ‘normal’ top-down routines that are constantly running.

“The emergence of theta/delta oscillations, particularly in medial temporal lobe sources, has been classically associated with REM sleep dreaming and related ‘visionary’ states. We propose that the observed emergence of theta/delta rhythmicity combined with the characteristic ‘collapse’ of alpha/beta rhythmicity under DMT may relate to the ‘DMT breakthrough experience’ – a perceptual mechanism by which the brain switches from the processing of exogenously incoming information to a state in which processing is endogenously-driven, as in classic REM sleep dreaming. This is further supported by the positive correlation we observed between participants’ ratings of the visual quality of their experiences and increases in theta and delta power – and decreases in alpha, especially evident once the (putatively) more functionally relevant oscillatory component of the EEG signal was isolated from the fractal component.”

The more bottom-up processes from inside the brain (endogenously: caused by factors inside the organism or system) are those that lead to the visions experienced.

“The increases in signal diversity found here, as elsewhere may be considered the positive complement of reduced alpha power and are consistent with the so-called ‘entropic brain hypothesis’ which proposes that within a limited range of states (i.e. within a critical zone) the richness of content of any given conscious state, can be meaningful indexed by the entropy of its underlying spontaneous brain activity.”

This links back to the Entropic Brain Hypothesis as proposed by Carhart-Harris et al. (2014, 2018). You can find an analysis of the 2018 paper here.

It’s also relevant for the REBUS model: relaxed beliefs under psychedelics. “…via their entropic effect on spontaneous cortical activity—
psychedelics work to relax the precision of high-level priors or beliefs, thereby liberating bottom-up information flow, particularly via intrinsic sources such as the limbic system.” (see here the analysis of Carhart-Harris & Friston, 2019)

“Finally, these results may shed light on some of the neural mechanisms associated to reports showing antidepressant effects of DMT and DMT-containing compounds. Increased alpha band power and decreased delta band power has been found in depressed populations and signal diversity has been found to index fluctuations in mood and depression. It is reasonable to consider that the massive changes in these measures induced by DMT may have implications for modelling and perhaps treating psychopathology.”

While lots of research still has to be done, it’s promising that psychedelics may target the underlying brain functions and structures that are ‘stuck’ in the ‘wrong’ settings for people with depression.

Summary of Neural correlates of the DMT experience as assessed via multivariate EEG