Lysergic acid diethylamide (LSD) use causes changes in the way that people think about time that may help develop drug therapies for people suffering from depression, according to a study published in the Journal of Psychopharmacology.

LSD is a synthetic hallucinogenic drug, which has long been used recreationally. Changes in the perception of time is a commonly-reported effect of LSD use. In particular, people who have taken large doses of LSD often experience a sense of timelessness and dissociation from one’s own personal history that has been called “ego-disintegration.”

Brain imaging research has shown that LSD use causes decreased activity in a part of the brain known as the default mode network (DMN), which has been linked with the experience of thinking about one’s own past.

A team of scientists led by Jana Speth, of the University of Dundee, sought to quantify these changes in time perception and their relationship with DMN activity in a controlled study of LSD use. Twenty volunteers participated in two separate laboratory sessions at least two weeks apart. Each participant was given a dose of LSD in one session and a placebo dose in the other, with half randomly assigned to receive the LSD first and half to receive the placebo first.

Two hours after receiving the LSD or placebo dose, participants’ brain activity was monitored using functional magnetic resonance imaging (fMRI), which indicates which parts of the brain are more or less active. Afterwards, participants were interviewed about what they had been thinking about while the fMRI measurements were being taken. Their responses were analyzed to determine the number of references to thinking about the past, present, and future.

Compared with the placebo condition, participants reported dramatically less thinking about the past after being administered with LSD. At the same time, fMRI analysis showed significantly lower DMN activity after using LSD than after receiving a placebo. These results support the view that at least some of the temporal perception effects of LSD use are caused by the action of LSD on the DMN system.

“Results revealed a selective effect of LSD on mental spaces linked to the past, i.e. there were significantly fewer cases of mental time travel to the past under LSD than placebo, and this effect correlated with the general intensity of LSD’s subjective effects,” Speth and her colleagues wrote in their study. “These outcomes shed light on the phenomenon of ego-dissolution and specifically a decomposition of the ‘narrative-self’ or ‘narrative identity’, which is strongly associated with autobiographical thought.”

The authors of the study suggest that these results may have implications for treatment of depression. Excessive focus on one’s own past is a symptom of depression, and previous brain imaging studies have found that people suffering from depression tend to have elevated levels of DMN activity in comparison to people without depression. If the chemical components of LSD that modulate DMN activity can be identified, it may one day be possible to exploit its potential to help control this harmful rumination on the past.