Giving psilocybin to rats made them more optimistic in the longer term, suggesting that the psychedelic substance could have great potential in treating a core symptom of depression in humans.
Psilocybin’s potential to safely and effectively treat mental illness appears to be highlighted with every new study into its effects. Now, Monash University researchers have added more evidence to the growing pile.
In a recent study, they found that giving psilocybin to rats improved their optimism over the long term. If the findings translate to humans, the naturally occurring psychedelic has great potential to treat a core symptom of depression.
“Our team found that rats given psilocybin were more motivated to explore their environment and perform reward-based tasks,” said Professor Jakob Hohwy from the Monash Center for Consciousness and Contemplative Studies (M3CS) and the study’s co-senior author. “These exciting results show the mechanisms of how psilocybin may work to increase optimism in an animal model, which we hope may translate to humans as well.”
The researchers used a computational model to understand the information-processing mechanisms underlying the effects of psilocybin and how the substance may change specific model parameters over time. Put simply, information processing theory compares the brain to a computer that works in a set sequence: receiving information, processing it, and delivering an output. Computational psychiatry is a growing field that aims to develop precise treatments for psychiatric disorders based on an individual’s specific information-processing mechanics.
Rats between eight and nine weeks old were administered either a single dose of psilocybin (1.5 mg/kg) or saline. From 24 hours after treatment, the rats were exposed to a reversal learning task, where they first had to learn a reward-stimuli association, then subsequently had to inhibit this learned association and learn a new one. It’s a test of cognitive flexibility. The rats completed the task over 14 experimental sessions on separate consecutive days.
Rats given psilocybin tended to achieve more rewards in the reversal learning task than control rats given saline, and their engagement increased over time. The control group also stayed in their cage significantly more than the psilocybin group, reflecting less frequent task engagement.
The computational results showed that psilocybin caused the rats to forget more about their previous beliefs when they received a reward compared to when they received a loss. These results, the researchers say, are reflective of ‘optimism bias,’ which is the tendency to overestimate the likelihood of positive events and underestimate the likelihood of negative ones.
The computational results also showed that psilocybin reduced loss aversion in rats in the longer term. The rats given psilocybin had more losses than the control group but still engaged more with the task, meaning they were less deterred from engaging in the task, despite the possibility of a loss.
The next step is further research to see if this effect translates to human subjects.
“Insights into the mechanisms of psilocybin allow us to unpack who may benefit from psychedelic therapies as well as who these treatments may not be beneficial for,” said Beth Fisher, who led the study with Hohwy. “With many people around the world affected by depression, our ultimate goal is to help build understanding of how psilocybin might be used to treat core symptoms people experience, such as diminished optimism, apathy and withdrawal from the world around them.”
The study was published in the journal Translational Psychiatry.
Source: Monash University via Medianet