In a study from the University of Cambridge, scientists found why common anti-depressants cause around half of users to feel emotionally “blunted.”
They found that the drugs affect reinforcement learning, an important behavioral process that allows people to learn from their environment.
A widely used class of antidepressants, particularly for persistent or severe cases, is selective serotonin reuptake inhibitors (SSRIs).
These drugs target serotonin, a chemical that carries messages between nerve cells in the brain and has been dubbed the “pleasure chemical.”
One of the widely reported side effects of SSRIs is “blunting,” where patients report feeling emotionally dull and no longer finding things as pleasurable as they used to.
Between 40% and 60% of patients taking SSRIs are believed to experience this side effect.
In the current study, the team tested healthy people and used escitalopram, an SSRI known to be one of the best-tolerated depression drug, for several weeks to see the impact of the drug on the participants’ cognitive performance.
In total, 66 volunteers took part in the experiment, 32 of whom were given escitalopram while the other 34 were given a placebo.
The team found no big group differences when it came to “cold” cognition—such as attention and memory. There were no differences in most tests of “hot” cognition—cognitive functions that involve our emotions.
However, the key finding was that there was reduced reinforcement sensitivity on two tasks for the escitalopram group compared to those on placebo.
Reinforcement learning is how we learn from feedback from our actions and environment.
The team found that people taking escitalopram were less likely to use positive and negative feedback to guide their learning of the task.
This suggests that the drug affected their sensitivity to the rewards and their ability to respond accordingly.
The team says emotional blunting is a common side effect of SSRI antidepressants.
This study showed that this is because they become less sensitive to rewards, which provide important feedback.
If you care about depression, please read studies that vegetarian diet may increase your depression risk, and Vitamin D could help reduce depression symptoms.
For more information about mental health, please see recent studies about 5 signs of depression you shouldn’t ignore, and results showing new drug could start fighting depression in just 2 hours.
The study was conducted by Professor Barbara Sahakian et al and published in Neuropsychopharmacology.
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