There is a growing interest in the medical use of psychedelic substances as preliminary studies using them for psychiatric disorders have shown positive results. In particularly, one of these
substances is N,N-dimethyltryptamine (DMT) an agonist serotonergic psychedelic that can induce
profound alterations in state of consciousness.
In this work, we propose a computational method based on machine learning as an exploratory
tool to reveal DMT-induced changes in brain activity using EEG data and provide new insights
into the mechanisms of action of this psychedelic substance. To answer these questions, we propose
a two-class classification based on (A) the connectivity matrix or (B) complex network measures
derived from it as input to a support vector machine We found that both approaches were able to
automatically detect changes in the brain activity, with case (B) showing the highest AUC (89%),
indicating that complex network measurements best capture the brain changes that occur due to
DMT use. In a second step, we ranked the features that contributed most to this result. For case
(A) we found that differences in the high alpha, low beta, and delta frequency band were most
important to distinguish between the state before and after DMT inhalation, which is consistent
with results described in the literature. Further, the connection between the temporal (TP8) and
central cortex (C3) and between the precentral gyrus (FC5) and the lateral occipital cortex (T8)
contributed most to the classification result. The connection between regions TP8 and C3 has been
found in the literature associated with finger movements that might have occurred during DMT
consumption. However, the connection between cortical regions FC5 and P8 has not been found
in the literature and is presumably related to emotional, visual, sensory, perceptual, and mystical
experiences of the volunteers during DMT consumption. For case (B) closeness centrality was the
most important complex network measure. Moreover, we found larger communities and a longer
average path length with the use of DMT and the opposite in its absence indicating that the balance
between functional segregation and integration was disrupted. This findings supports the idea that
cortical brain activity becomes more entropic under psychedelics.
Overall, a robust computational workflow has been developed here with an interpretability of how
DMT (or other psychedelics) modify brain networks and insights into their mechanism of action.
Finally, the same methodology applied here may be useful in interpreting EEG time series from
patients who consumed other psychedelic drugs and can help obtain a detailed understanding of
functional changes in the neural network of the brain as a result of drug administration.