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Depression can be identifiable in the eye. The pupil in our eye reacts to more than just changing light conditions.

Max Planck Institute Munich –

When people can gain or lose something, their pupils dilate slightly. Researchers have found that this dilation is less in acutely depressed patients than in healthy people—the more severe the illness, the less the dilation of the inner eye. In the long term, this finding could lead to a more accurate diagnosis that is not just based on what the patients say but is biologically based. This could also lead to more individualised treatment with medication.

Do rewards not work for depressed people?

For decades, researchers have been trying to find out whether depressed patients value rewards less than non-depressed people. Study participants at the Max Planck Institute for Psychiatry (MPI) now played a simple game in a magnetic resonance imaging (MRI) scanner, where they could win a small amount of money. A clear incentive that leads to the dilation of the pupil in healthy people. The researchers measured the pupils of their study participants extremely accurately and at extremely high speed: Using a special test setup, they were able to take 250 pictures per second – by comparison, we only blink every four to six seconds.

The severity of depression correlates with pupil response.

The result: for the first time, MPI scientists were able to prove the link between pupil dilation in response to an expected reward and the severity of depression in the respective test person. The more severe the symptoms were, the less dilated the pupils were.

The study shows that the prospect of a reward in severely depressed patients does not lead to the same behavioural activation as in healthy people. Their nervous system might activate less even when they have such a positive expectation. «We suspect that there is a physiological system behind this that can partly explain the often reported drive disorder in patients,» says study leader Victor Spoormaker.

Original publication: Max Schneider, Immanuel G. Elbau, Teachawidd Nantawisarakul, Dorothee Pöhlchen, Tanja Brückl, BeCOME Working Group, Michael Czisch, Philipp G. Saemann, Michael D. Lee, Elisabeth B. Binder and Victor I. Spoormaker: Pupil Dilation during Reward Anticipation Is Correlated to Depressive Symptom Load in Patients with Major Depressive Disorder; Brain Sci. 2020, 10(12), 906; https://doi.org/10.3390/brainsci10120906

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