Implications for psychedelic-assisted psychotherapy : a functional magnetic resonance imaging study with psilocybin
R. L. Carhart-Harris, R. Leech, T. M. Williams, D. Erritzoe, N. Abbasi, T. Bargiotas, P. Hobden, D. J. Sharp, J. Evans, A. Feilding, R. G. Wise and D. J. Nutt
British Journal of Psychiatry, 2012, 200, 238-244.
Doi : 10.1192/bjp.bp.111.103309
Psilocybin is a classic psychedelic drug that has a history of use in psychotherapy. One of the rationales for its use was that it aids emotional insight by lowering psychological defences.
To test the hypothesis that psilocybin facilitates access to personal memories and emotions by comparing subjective and neural responses to positive autobiographical memories under psilocybin and placebo.
Ten healthy participants received two functional magnetic resonance imaging scans (2mg intravenous psilocybin v. intravenous saline), separated by approximately 7 days, during which they viewed two different sets of 15 positive autobiographical memory cues. Participants viewed each cue for 6 s and then closed their eyes for 16 s and imagined re-experiencing the event. Activations during this recollection period were compared with an equivalent period of eyes-closed rest. We split the recollection period into an early phase (first 8 s) and a late phase (last 8 s) for analysis.
Robust activations to the memories were seen in limbic and striatal regions in the early phase and the medial prefrontal cortex in the late phase in both conditions (P50.001, whole brain cluster correction), but there were additional visual and other sensory cortical activations in the late phase under psilocybin that were absent under placebo. Ratings of memory vividness and visual imagery were significantly higher after psilocybin (P50.05) and there was a significant positive correlation between vividness and subjective wellbeing at follow-up (P50.01).
Evidence that psilocybin enhances autobiographical recollection implies that it may be useful in psychotherapy either as a tool to facilitate the recall of salient memories or to reverse negative cognitive biases.
Psilocybin is a classic psychedelic (‘mind-manifesting’) drug, pharmacologically related to the prototypical psychedelic, lysergic acid diethylamide. Psychedelic drugs were used extensively in psychotherapy in the 1950s to lower psychological defences and facilitate emotional insight.1 In cognitive terms, the ‘lowering of defences’ may be thought of as a decrease in top-down emotional control. There are several reports in this literature of spontaneous autobiographical recollections or ‘relivings’ under psychedelics2 – similar in some respects to the dream-like sequences seen on stimulation of the medial temporal lobes3 or to the flashback phenomena seen in post-traumatic stress disorder (PTSD).4 In a previous psilocybin functional magnetic resonance imaging (fMRI) study by our group,5 one individual reported a striking reliving under the drug, further motivating us to test this phenomenon in a controlled manner. We also observed large decreases in resting state activity in the medial prefrontal cortex after psilocybin.5 The medial prefrontal cortex is known to exert top-down inhibitory control over limbic activity,6 so a psilocybin-induced deactivation of the medial prefrontal cortex – leading to a disinhibition of limbic activity – may explain the occurrence of spontaneous recollections in the psychedelic state.
Thus, the present study sought to test the hypothesis that psychedelic drugs facilitate autobiographical recollection, using psilocybin and a blocked fMRI paradigm involving personal memory cues. Spontaneous relivings under psychedelics are often explicitly linked to past traumata;2 however, we used only positive memory cues in order to minimise the risk of adverse reactions. We predicted that psilocybin would augment subjective and neural responses to personal memories. Based on previous studies implicating medial temporal and visual association regions in vivid autobiographical recollections,7–9 we predicted that psilocybin would increase activations in these specific regions.