The study was carried out in collaboration with researchers at Compass Pathways, Boehringer Ingelheim, and the University of Cambridge. 

Negative affective biases are a core feature of major depressive disorder. Affective biases occur when emotions alter how the brain processes information and negative affective biases are thought to contribute to the development and continuation of depressed mood. 

The research team used an affective bias test, based on an associative learning task, to investigate the effects of rapid-acting antidepressants (RAADs) in rats.  They found that all the treatments were able to reduce negative affective biases associated with past experiences but there were additional characteristics of the dissociative anaesthetic, ketamine, and the serotonergic psychedelic, investigational COMP360 psilocybin (Compass Pathways’ proprietary formulation of synthetic psilocybin), which could explain why the effects of a single treatment can be long-lasting. 

The findings suggest that these sustained effects are due to adaptive changes in the brain circuits which control affective biases, and these can influence how past experiences are remembered. The effects at low doses were very specific to affective bias modulation and were localised to the prefrontal cortex of the brain, a region known to play an important role in mood. 

Read the full University of Bristol news item

'Rapid-acting antidepressants modulate affective bias in rats' by Justyna K. Hinchcliffe et al. in Science Translational Medicine [open access]