New Study Reveals Specific Effects Of One Of The Best-tolerated Anti-Depressants On People
Common Anti-Depressant may alleviate some of the emotional suffering associated with depression, but it also appears to diminish the ability to experience pleasure as explained in the new study published today.
Selective serotonin reuptake inhibitors – in short SSRIs – are a family of antidepressants that are often used, especially for chronic or severe instances.
These drugs work on serotonin, which is called the “pleasure chemical” because it sends messages between nerve cells in the brain.
Patients who use SSRIs often report experiencing “blunting,” in which they feel emotionally flat and no longer find life as enjoyable as they once did. This adverse effect is thought to affect between 40 and 60 percent of SSRI users.
Most SSRI studies have only looked at their short-term effects, despite the fact that clinically these medications are used on a chronic basis for depression.
Researchers from the University of Cambridge and the University of Copenhagen worked together to try to figure this out. They found healthy volunteers and gave them escitalopram, an SSRI that is known to be one of the best tolerated. Over the course of several weeks, they took a set of cognitive tests to see how the drug affected their performance.
The study had 66 individuals in all, 32 of whom received escitalopram while the other 34 received a placebo.
Volunteers completed a thorough set of self-report questionnaires, took the medication or a placebo for at least 21 days, and underwent a battery of tests to gauge their cognitive abilities, including learning, inhibition, executive function, reinforcing behavior, and decision-making.
Today, the findings of the research were published in the journal Neuropsychopharmacology.
When it came to “cold” cognitive skills, such as attention and memory, the team didn’t find any big differences between the groups. Most tests of “hot cognition,” or mental processes involving our emotions, showed no changes.
The main surprising discovery, however, was that the escitalopram group performed two tasks with less reinforcement sensitivity than the placebo group did. Learning via experience and practice, is often known as reinforcement learning.
The researchers employed a “probabilistic reversal test” to evaluate reinforcement sensitivity. A person taking part in this task would usually see two stimuli, A and B.
If they selected option A, they would be rewarded four out of five times; if they selected option B, they would only be rewarded once out of five times.
The rule would not be told to the volunteers; they would have to figure it out on their own. At some point in the experiment, the odds would change, and the volunteers would have to figure out a new rule.
The team found that people who took escitalopram were less likely to use positive and negative feedback to help them learn the task than people who took a placebo. This suggests that the drug changed how they felt about the rewards and how they could respond to them.
The discovery may also explain the one difference the scientists identified in the self-reported questionnaires: participants on escitalopram had greater problems attaining orgasm during sex, a common side effect.
“Emotional blunting is a common side effect of SSRI antidepressants, points out senior author prof. Barbara Sahakian.
“In a way, this may be in part how they work – 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.”
“Our findings provide important evidence for the role of serotonin in reinforcement learning,” adds first author Dr. Christelle Langley.
“We are following this work up with a study examining neuroimaging data to understand how escitalopram affects the brain during reward learning.”
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