Taking lysergic acid diethylamide – better known as LSD – could help people who suffer from depression to overcome their condition by preventing them from “ruminating” on past experiences. Several studies have shown that low mood is often associated with a tendency to dwell on one’s own history, yet new research indicates that LSD may inhibit the brain network that mediates this type of “mental time travel.”

According to the new study, which appears in the Journal of Psychopharmacology, “mental time travel refers to the ability of humans to mentally project themselves backwards and forwards in time, to recollect aspects of past autobiographical episodes or imagine future experiences.” Several scholars have remarked that this ability to access and continually replay previous life events contributes significantly to a person’s sense of self and identity, often referred to academically as the “ego.”

A particular brain network known as the default-mode network (DMN) has been identified in several studies as the key circuit mediating this capacity for mental time travel. Research has shown that people with higher rates of connectivity in the DMN tend to reflect on the past more, engage in more ruminative thought, and suffer from depression and general low mood.

However, functional magnetic resonance imaging (fMRI) scans on people under the effects of a range of psychedelic drugs have indicated that such substances actually decrease the activity of the DMN. This effect has subsequently been cited as a key factor in the ability of these substances to induce what researchers call “ego dissolution,” whereby users often experience a subjective decomposition of their sense of self.

Taking this work a step further, a team of researchers led by Jana Speth of the University of Dundee set out to determine if LSD can reduce the tendency for mental time travel.

^{Excessive ruminating about the past has been associated with low mood and depression. Oleg Golovnev/Shutterstock}

To achieve this, the researchers took fMRI scans of volunteers’ brains immediately after administering them with either LSD or a placebo. They then conducted a series of interviews with participants, before analyzing the transcripts of these conversations in order to determine how the language used differed between those who had received the drug and those who had not.

In particular, the study authors were on the lookout for linguistic constructs known as “theta roles,” which indicate mentalizations of particular temporal domains, signifying mental time travel to the past, present, and future.

Results showed that those who had received LSD used far fewer references to the past than those who received the placebo, suggesting a decrease in mental time travel and an experiential focus on the present. Importantly, the extent of this effect was directly correlated with the degree to which the connectivity of the DMN was dampened by the effects of the drug, implying that LSD can indeed inhibit the brain regions responsible for mental time travel.

Though it is yet to be established if this trait persists after the acute effects of the drug wear off, the ability of LSD to act on this key neural circuit could represent a major opportunity for therapists looking for novel methods of combating depression. At present, several mindfulness-based treatments for depression encourage patients to adopt a more present-focused mode of thinking, and the capacity of LSD to inhibit the DMN could potentially help more patients achieve this.

Whether or not this characteristic of LSD really does alleviate long-term depression will have to be explored in future studies, although the researchers point to previous and ongoing work into the positive impact of psychedelic substances on mood disorders to suggest that “such enduring effects seem likely.”