A high-speed camera provides information about pupil size. Credit: Martin Otter MPI Psychiatry
Scientists at the Max Planck Institute of Psychiatry measured the pupillary reaction of participants while they solved a task. In healthy participants, pupils dilated during the task in anticipation of a reward, but this response was less pronounced in participants with depression.
“The reduced pupil response was particularly noticeable in patients who could no longer feel pleasure and reported a loss of energy,” explains Andy Brendler, first author of the study. This feeling of apathy is one of the most common symptoms of depression.
“This discovery helps us better understand the physiological mechanisms behind apathy,” explains Victor Spoormaker, head of the research group. Among other things, the pupillary reaction is a marker of the activity of the locus coeruleus, the brain structure with the highest concentration of noradrenergic neurons in the central nervous system.
Noradrenergic neurons respond to the neurotransmitter noradrenaline, an essential component of the stress response and the positive regulation of arousal, in other words the activation of the nervous system. “The reduced pupillary response in patients with more apathy indicates that the lack of activation of the locus coeruleus is an important physiological process that causes the feeling of apathy,” says Spoormaker.
Correlation between pupil dilation and number of symptoms in depressed patients. (a) original study; (b) replication study; and (c) combined samples. Estimation of the correlation between pupil dilation during reward anticipation and the number of depressive symptoms taking into account the measurement uncertainty of each measurement (represented by vertical and horizontal error bars), y including regression lines (a, b and c, left panels). The Bayesian model estimated the true correlation while accounting for measurement uncertainty by sampling from a multivariate Gaussian distribution, leading to a posterior distribution that indicates the probability of the modeled correlation (a, b and c, right panels). Credit: Scientific reports (2024). DOI: 10.1038/s41598-023-48792-0
The study also found that student response was lower when participants had depressive symptoms. This replicates the results of a previous study conducted by the same research group. The replicability of neuropsychiatric methods is more the exception than the rule and demonstrates the reliability of pupillometry as a method.
Pupillometry could be used as a complementary diagnostic method. This could also contribute to the development of individualized treatment strategies for depression. For example, if a patient has a significantly reduced pupillary response, antidepressants that act on the noradrenergic system might be more effective than other medications. The dosage of the medication could also be optimized based on the student’s response.
Given that approximately 30% of depressed patients do not improve with currently available medications, there is an urgent need to understand the physiological mechanisms underlying depression and refine diagnosis and treatment accordingly.
The article is published in the journal Scientific reports.
More information:
Andy Brendler et al, Assessment of hypoarousal during reward anticipation with pupillometry in patients with major depressive disorder: replication and correlations with anhedonia, Scientific reports (2024). DOI: 10.1038/s41598-023-48792-0
Provided by the Max Planck Society
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