2024-01-31 09:04:42
When suffering from clinical depression, people often experience a loss of motivation and even a lack of fun. A recent study published in Scientific Reports reveals the physical manifestation of this mental state: the absence of “pupil dilation.” When reward-related neural pathways in the brain are activated, healthy people’s pupils dilate for about six seconds in anticipation of an upcoming reward. However, depressed patients did not respond similarly when faced with potential rewards, a phenomenon that was particularly evident in those who no longer felt pleasure and reported a lack of energy.
Pupil dilation is part of the nervous system’s response to stress or excitement and is triggered when the locus coeruleus in the brainstem produces the neurotransmitter norepinephrine. In those with depression who experience a sense of joylessness, or “emotional numbness” and a “lack of joy,” the lack of pupil dilation may suggest that reward circuits in the brain have been affected.
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In a new study by Andy Brendler and his team, 40 people with unmedicated depression and 31 healthy people completed 30 trials of three different tasks on a computer. At the same time, their pupil size was measured using an eye tracker inside the MRI machine. In each task, a computer screen would use images to prompt the possibility of a financial reward and then prompt a response after a flash of light. When the participant responds fastest, a reward of 1 Euro will be displayed on the computer screen.
Repeatable psychological experiments
In one task, participants were given six seconds to anticipate receiving a monetary reward. In the other two tasks, there is no chance of receiving rewards. (Photo/Scientific Reports) Advertisement (Please continue reading this article)
About 1 in 10 people worldwide experience depression, but there are currently no approved biomarkers to diagnose the disease. It is usually diagnosed using behavioral assessment. Eye tracking can be used as a clinical test to classify people with depression or monitor their response to treatment.
In a 2018 study of 46 people without a diagnosis of depression, the same research team found that the anticipation of monetary rewards consistently caused participants’ pupils to dilate.
Importantly, the latest findings are a valuable replication of the team’s 2020 study involving 41 people with unmedicated depression and 25 healthy people, and their latest paper increases the combined sample to 136 people.
Confidence in psychological research has declined in recent years, and findings often fail to be replicated. By showing that their findings can be replicated, the authors say they are directly addressing this issue, thereby increasing confidence in their results.
The paper was published in Scientific Reports.
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Source of first picture: DALL.E
Image Source:Scientific Reports cc By4.0
Reference papers:
1.Assessing hypo-arousal during reward anticipation with pupillometry in patients with major depressive disorder: replication and correlations with anhedoniaScientific Reports
Further reading:
1.Chinese scientists discover: “New antidepressant” helps cancer treatment
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