N,N-Dimethyltryptamine (DMT), a potent serotonin-2A receptor agonist, elicits intense psychedelic experiences and has become a focus of interest in neuroscience and mental health research. While EEG studies of psychedelics typically report reduced alpha power, increased delta power, and enhanced signal complexity-primarily assessed using Lempel-Ziv complexity (LZc)-less is known about DMT's effects on other complexity metrics, EEG-based connectivity, and emotional correlates. This study investigated the effects of intravenous DMT versus saline placebo in 13 healthy participants using EEG. We analyzed spectral power, brain signal complexity, and functional connectivity, and examined their associations with emotional responses and subjective intensity ratings. Four complexity measures were evaluated: Lempel-Ziv-Welch (LZW) complexity, Higuchi fractal dimension (HFD), permutation entropy (PE), and waveform complexity (WC). Connectivity was assessed using weighted symbolic mutual information (wSMI), with network segregation and efficiency inferred from clustering coefficient and path length. Emotional correlates included beta-to-alpha ratio (BAR, an indicator of arousal) and frontal alpha asymmetry (FAA, an indicator of well-being). DMT significantly reduced broadband wSMI connectivity, segregation, and efficiency, particularly in alpha and beta bands in posterior and frontoparietal regions. Complexity metrics positively correlated with subjective intensity; HFD and PE were the most sensitive, revealing increased complexity in beta/gamma and decreased complexity in delta/theta/alpha bands under DMT. BAR and FAA both increased under DMT, correlating with perceived intensity. These findings suggest that DMT induces greater neural unpredictability and emotional arousal, consistent with the Entropic Brain theory. The results highlight a dynamic brain state that may support therapeutic brain network reorganization relevant for psychiatric treatment.
