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Perhaps you have already observed this: If we win something or are threatened with defeat, the pupils dilate automatically.

This is due to our nervous system, which is activated in anticipation of a positive gain or a negative loss.

We become more attentive to what is happening around us so that we can react accordingly.

The eye hole widens so that we can perceive more.

Scientists have long suspected that people who suffer from depression value rewards less than non-depressed ones.

So far, however, no evidence has been found for this hypothesis.

Researchers at the Max Planck Institute for Psychiatry have now started an interesting study: 161 study participants took part in a simple game in which they could win a small amount of money.

A clear incentive that leads to the dilatation of the pupil in healthy people.

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The result showed that people who suffer from depression reacted less strongly

During the study it was shown that the more severe the depressive symptoms were in the patient, the less the pupils opened.

This enabled the psychologists to prove for the first time that the prospect of a reward in severely depressed patients does not lead to the same behavioral activation as in healthy people.

They published the results of their study in the journal “Brain Sciences”.

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To determine how each subject's eyes reacted to the game, they were observed in a magnetic resonance imaging (MRI) scanner.

At the same time, the researchers measured the pupils of their study participants precisely at an extremely high speed.

They took up to 250 frames per second.

For comparison: we blink every four to six seconds.

In this way, the scientists succeeded in drawing a fairly precise picture of how far the subjects' pupils dilated - or not.

The study indicates that the nervous system of depressed patients is less able to activate itself, even with positive expectations.

The director of studies says:

We suspect that there is a physiological system behind this that can partially explain the often reported drive disorder in patients. 

Victor Spoormaker, head of the psychophysiology laboratory at the Max Planck Institute for Psychiatry  

Can the pupil be the key to new therapies?

The new findings could make diagnosis easier in the future.

Because then this is not only based on the statements of the patient, but can also be justified biologically.

In this way, depression can be diagnosed more effectively than before.

In addition, the therapy with medication could be adapted more individually and better - because depending on how far the inside of the eye expands in actually positive situations, the therapists can determine how severe the depression has advanced.

Source: Unsplash.com/Marina Vitale

The researchers at the Max Planck Institute even go one step further: They assume that psychiatric illnesses should be divided up differently than in the previous diagnostic groups.

Biological factors such as the dilation of the pupil would then also be decisive.

Since these factors are clearly measurable, the diagnostic confidence would increase.

Depressed patients who react less strongly with their pupils would then, for example, form their own subgroup.

This approach is now to be investigated and pursued more closely in further studies.