Behavioral Shifts in Natural Speech, Language, and Facial Expression Following Ayahuasca Ceremonies

Background: Within the last decade, ayahuasca, a brew containing a serotonin 2A receptor agonist (i.e., a classical psychedelic compound), has received increased attention as a possible intervention for posttraumatic stress disorder. Ayahuasca has demonstrated potential for long-term symptom reduction, but the biobehavioral changes caused by ayahuasca have not been defined quantitatively or investigated as potentially related to psychopathology. Methods: We used ecological momentary assessment to investigate biobehavioral changes following the administration of an ayahuasca ceremony by Shipibo–Conibo ayahuasqueros in 15 participants (11 male, 4 female; 1 Asian, 14 Caucasian; and 8 military veterans with reported trauma, 7 participants without reported trauma). Participants recorded video “selfies” describing the past hour, multiple times daily, before, during, and after a week of ayahuasca ceremonies. Linguistic, acoustic, and facial movement data were extracted from the videos. Results: Multilevel modeling and feature selection using Least Absolute Shrinkage and Selection Operator (LASSO) regression indicated that time relative to ayahuasca use could be reliably identified using a comprehensive biobehavioral feature set. Results indicated that participants’ language use changed following ayahuasca administration, with significant differences in language content, structure, sentiment, and word count. Minor effects on head movement were demonstrated. Conclusions: The biobehavioral changes waned over the week following ayahuasca administration. Implications for further research into the characterization of changes related to psychedelics and the clinical application of psychedelic substances are discussed.