“Dullness”, a feeling in which the person feels apathetic to emotions and without energy to perform daily tasks, is reported by regarding half of people who use common antidepressants.
After a groundbreaking study, scientists at the University of Cambridge believe they have discovered why this occurs. The work was published in the journal Neuropsychopharmacology, this Monday (1/23).
The most popular drugs in the antidepressant class are the selective serotonin reuptake inhibitors (SSRIs), such as escitalopram. The drug targets serotonin, a chemical that transmits messages between nerve cells.
Reports of lack of pleasure
The survey had 66 volunteers. For 21 days, 32 of them received escitalopram and the other 34 took a placebo drug.
Participants also completed questionnaires and took tests to assess cognitive functions such as learning ability, inhibition, task execution and decision making.
The team found no significant differences between the two groups on topics related to attention and memory. But there was a predominance of reports of numbness and lack of pleasure among the group that used the drug.
stimulus and response
In a second step of the work, the researchers used a ‘probabilistic reversal test’ to assess reinforcement learning. In this task, participants were given two stimuli, indicated by the letters A and B. If they chose A four out of five times, they received a reward. If they chose B, they would receive the reward only once in five.
The volunteers would have to learn the rule by themselves and, at some point in the experiment, it would be changed and the participants would need to get the new rule.
The team found that participants taking escitalopram were less likely to orient their task learning towards the positive stimulus, suggesting a lower sensitivity to the pleasure of receiving rewards.
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