Common antidepressants can make many users feel emotionally ‘dulled’, according to a study that provides new insight into how the drug works and possible side effects.
The study, published Monday in the journal Neuropsychopharmacology, shows that drugs affect reinforcement learning. Reinforcement learning is an important behavioral process that allows us to learn from our environment.
A widely used class of antidepressants, especially in persistent or severe cases, is the selective serotonin reuptake inhibitors (SSRIs). These drugs target serotonin, a chemical that carries messages between nerve cells in the brain and is called the “pleasure chemical.”
One widely-reported side effect of SSRIs is “slowness,” the researchers said, with patients reporting feeling emotionally sluggish and unable to find things they enjoyed as much as they used to.
They say that 40 to 60 percent of patients taking SSRIs are thought to experience this side effect.
“Emotional blunting is a common side effect of SSRI antidepressants,” said Professor Barbara Sahakian, senior author of the study at the University of Cambridge, UK.
“In a way, this may be part of what they do. It takes away some of the emotional pain that people experiencing depression feel, but unfortunately it also takes away some of the fun.” It seems that
According to the study, this is because people become less sensitive to rewards that provide important feedback.
Most studies on SSRIs to date have only investigated short-term use, but in clinical use for depression, these drugs are used chronically over long periods of time.
Researchers at the University of Cambridge, in collaboration with Denmark’s University of Copenhagen, recruited healthy volunteers and administered them over several weeks with escitalopram, the best-tolerated SSRI known.
They evaluated the effects of drugs on performance with a battery of cognitive tests. In total he had 66 volunteers in the study, 32 of whom received escitalopram and the rest of his 34 received placebo.
Volunteers took the drug or placebo for at least 21 days, completed a series of comprehensive self-report questionnaires, and underwent a battery of tests assessing cognitive functions including learning, inhibition, executive function, reinforcing behavior, and decision-making. .
The team found no significant differences between the groups when it came to “cold” cognitions such as attention and memory.
Most tests of “hot” cognition (cognitive functions with emotion) showed no difference.
A key finding, however, was a reduction in reinforcement sensitivity in two tasks in the escitalopram group compared to the placebo group, the researchers said.
Reinforcement learning, they said, is a way to learn from behavior and feedback from the environment.
“Our findings provide important evidence for the role of serotonin in reinforcement learning,” said co-lead author Christelle Langley, also from Cambridge University.
“We continue this work with studies examining neuroimaging data to understand how escitalopram affects the brain during reward learning,” said Langley.
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