Escitalopram is one of the most tolerable selective serotonin reuptake inhibitors (SSRIs), used clinically over a longer period to treat depression. However, between 40% to 60% of patients who take SSRIs experience ‘blunting,’ described as feeling like one’s emotions are dulled not finding pleasure doing the things they once did, according to investigators who published the results of a recent study in Neuropsychopharmacology.
Investigators discovered that SSRIs like escitalopram affect reinforcement learning, a behavioral process that enables us to learn from our environment. Their impact on learning could explain why nearly 50% of users feel emotionally blunted.
“They take away some of the emotional pain that people who experience depression feel, but, unfortunately, it seems that they also take away some of the enjoyment. From our study, we can now see that this is because they become less sensitive to rewards, which provide important feedback,” said Barbara Sahakian, senior author, Department of Psychiatry at the University of Cambridge, and a Fellow at Clare Hall, in a recent press release.
But investigators wanted to understand its long-term effect on cognitive well-being. Teams from the University of Cambridge and the University of Copenhagen enrolled 66 volunteers into a study that evaluated how escalopram would affect healthy individuals over several weeks. They would gauge the SSRI impact by having participants take a series of cognitive tests after at least 3 weeks.
About half of the participants (32 participants) were administered escitalopram while the control arm received a placebo (34 participants). After 21 days, the participants filled out self-report questionnaires that assessed cognitive functions such as learning, inhibition, executive function, reinforcement behavior, and decision-making.
The results suggest that escitalopram affected the participant’s sensitivity to rewards. This means that participants did not rely on feedback (in the form of rewards) to guide their decision-making as much as the control group. However, the SSRI in review did not significantly decrease ‘cold’ cognition skills, like attention and memory, or emotional cognition (hot), compared to individuals who are not on an SSRI, according to researchers.
Researchers tested cognitive function with a ‘probabilistic reversal test,’ showing participants 2 stimuli, A or B. The likelihood of reward was higher if participants chose option A, with a 4 out of 5 chance of reward, compared to a 1 of 5 chance of being rewarded with option B. Further, participants needed to observe and learn these rules themselves. They were also responsible for adapting when the probabilities for rewards changed.
“Our findings provide important evidence for the role of serotonin in reinforcement learning. We are following this work up with a study examining neuroimaging data to understand how escitalopram affects the brain during reward learning,” said co-first author Christelle Langley, Department of Psychiatry, in the press release.
University of Cambridge. Scientists explain emotional ‘blunting’ caused by common antidepressants. January 22, 2023. Accessed January 23, 2023. https://www.eurekalert.org/news-releases/976960