Lysergic acid diethylamide (LSD) reduces activity in the emotion processing centre of the human brain known as the amygdala, according to a study recently published in Translational Psychology.

LSD is a potent psychoactive drug known to alter perception, awareness and emotions by over-activating specialised serotonin receptors in the brain. The need to study the effects of LSD for potential use in research and clinical practise is increasing, because it is thought to reduce anxiety in patients who are diagnosed with a life-threatening illness. Although the basic psychological effects of LSD are understood, data examining the effect of LSD on emotion processing in humans is limited.

A team of scientists from the University of Basel, Switzerland recruited 20 healthy participants (9 males, 11 females) to take part in a double-blind clinical trial that investigated the effects of LSD on emotion processing.

Participants received a small dose of LSD or a placebo before undergoing an fMRI scan to measure their brain activation whilst they carried out a gender identification task using stimuli that displayed a range of human emotion. It was found that participants who had taken LSD had reduced activation of the left amygdala and right medial prefrontal cortex (mPFC) (involved in processing risk and fear) in response to being shown images of fearful faces.

The results suggest that even a small amount of LSD interferes with the activity in brain regions that control emotion processing. More specifically, it was found that LSD produces a selective deficit in the ability to recognise fearful faces. Furthermore, the study found that LSD specifically affected the left amygdala, which previous studies have suggested to be involved in processing negative facial expressions. As mentioned above LSD acts mainly on serotonin receptors which are abundant in the amygdala, which provides a pharmacological explanation for the effect of LSD in this area.

The study also indicated a decrease in activity in the right mPFC which forms part of a neural network with the amygdala involved in emotion processing. This suggests that LSD also decreases the functional connectivity between these two brain regions after being exposed to fearful stimuli.

The results of this study suggest that psychoactive substances such as LSD have the potential to be used as a treatment for conditions such as depression and anxiety because it can reduce the perception of negative emotions.