The eyes are the window to the soul, they say – some people also say “mirror”. The idea behind it: eyes express inner feelings directly – they open up insights for us that would otherwise remain inaccessible. Researchers at the Max Plack Institute for Psychiatry in Munich (MPI) found out in a study with severely depressed patients that this is actually true in a very practical way: There are actually physiological bases for this assumption.

In people with depression, the main symptoms are a decreased ability to enjoy joy and lack of drive. In this context, scientists have long asked themselves how exactly this ailment is related to the reward center in the brain. If a person is excited, for example because he has won something in a game or receives a special reward, then the pupils dilate slightly. The researchers at the MPI have now been able to demonstrate that this regulation is disturbed in depressed people.

Eye tracker with high frequency As part of the study, participants played a game in the magnetic resonance imaging (MRI) scanner, in which small sums of money could be won. Fast eye trackers were positioned behind the presentation screen, with which eye movements were measured with high precision with 250 images per second. In the game, the participants were exposed to three different stimuli: the prospect of reward (“reward stimulus”), a neutral stimulus (“neutral stimulus”) and a control stimulus for which no reaction was provoked (“nonresponse stimulus”).

There was then a clear difference with the first suggestion: If there was a gain, the pupils of the depressed persons moved significantly less than those of the participants from the healthy control group. A correlation between the dilatation of the pupil and the severity of the depression could also be established.

Basis for extended diagnostics The study thus shows that a reward effect for depressed people is actually less attractive. As a result, the prospect of it activates the sick person’s nervous system less than it does in the case of non-sick people. Head of Studies Prof. Dr. Victor Spoormaker and his team suspect “a physiological system that can partially explain the often reported drive disorder in patients”. The MPI considers biologically measurable factors to be useful in order to be able to offer more individual treatment methods in the course of more accurate diagnostics. For example, a more targeted drug therapy could be offered to patients whose pupils react less strongly when they are rewarded. A lot of research will be necessary before a new classification key can be developed from this. (bsc)