Decreased mental time travel to the past correlates with default-mode network disintegration under lysergic acid diethylamide
Carhart-Harris, R. L., Feilding, A., Kaelen, M., Nutt, D. J., Schloerscheidt, A. M., Speth, C., Speth, J.
This double-blind placebo-controlled study (n=20) investigated the effects of LSD (75 μg/70kg) in relation to participants' ability to mentally project themselves backwards and forwards in time, based on brain activity measures and subjective reports that were analyzed by six blinded qualitative proof raters. There were significantly fewer cases of mental time travel to the past under LSD, meaning that they were less likely to recollect aspects of the past autobiographical self, and this phenomenon was correlated with the decreased integrity of the Default Mode Network.
Abstract
Introduction: This paper reports on the effects of LSD on mental time travel during spontaneous mentation.Methods: Twenty healthy volunteers participated in a placebo-controlled crossover study, incorporating intravenous administration of LSD (75 μg) and placebo (saline) prior to functional magnetic resonance imaging (fMRI). Six independent, blind judges analysed mentation reports acquired during structured interviews performed shortly after the functional magnetic resonance imaging (fMRI) scans (approximately 2.5 h post-administration). Within each report, specific linguistic references to mental spaces for the past, present and future were identified.Results: revealed significantly fewer mental spaces for the past under LSD and this effect correlated with the general intensity of the drug’s subjective effects. No differences in the number of mental spaces for the present or future were observed. Consistent with the previously proposed role of the default-mode network (DMN) in autobiographical memory recollection and ruminative thought, decreased resting-state functional connectivity (RSFC) within the DMN correlated with decreased mental time travel to the past.Discussion: These results are discussed in relation to potential therapeutic applications of LSD and related psychedelics, e.g. in the treatment of depression, for which excessive reflection on one’s past, likely mediated by DMN functioning, is symptomatic.