It is written on our faces: Whether we experience joy or negative emotions such as disgust or fear is shown by the characteristic features of our facial expressions. German researchers have now investigated the question of whether mice can also see what they are feeling right now. They were able to confirm that the rodents also show a typical facial expression with certain emotions. This finding can now also be used to research the neural basis of emotions in humans, the scientists say.
“Yuck!”, Or “tasty!”, “Hooray!”, Or “such bad luck!” … What goes through the mind of a fellow human being becomes visually noticeable, because the basic features of the emotional facial expressions are the same for all people. For example, if we are disgusted with something, we turn our noses, twist our upper lip asymmetrically and make our eyes narrow. These are innate reactions, because the typical emotional facial expressions of humans can already be demonstrated in babies. In keeping with this, we also develop an eye for these signs, which enables us to read the faces of our fellow human beings.
Analytical look at mouse faces
The faces of animals, on the other hand, appear to us mostly rather expressionless. However, as the study by the researchers at the Max Planck Institute for Neurobiology in Martinsried shows, emotional facial expressions are not only typical of humans. There is a reason that they looked closely at the mouse, of course: in many studies, rodents serve as a model for humans – including when researching the neuronal basis of emotions. In order to investigate the facial expressions of mice, the scientists captured the faces of experimental animals when they had certain emotional experiences during experiments. The respective images were then analyzed using machine image processing methods.
In this way, the researchers were able to demonstrate that the face of a mouse looks different in a characteristic way when it experiences joy, disgust, malaise, pain or fear. For example, when the animals tried a slightly salty liquid, a “satisfied” expression was formed, while a very salty solution caused a typical “disgusting expression”. “People can only see a subtle change in the rodent’s face – but we can only assign the emotion behind it with a lot of experience,” explains the first author of the study Nejc Dolensek. Your digital analysis method, on the other hand, can capture mouse emotions easily and objectively using the characteristic patterns.
Research potential
The system is even able to measure the relative strength of the emotions, the scientists report. It also showed how this level of reaction can depend on the context: “Mice who licked a sugar solution showed much happier facial expressions when they were hungry than when they were full,” reports co-author Nadine Gogolla. These and other experimental results show that a certain emotion is reflected qualitatively and quantitatively in the facial expressions of the animals, the researchers sum up.
They were able to further substantiate this result: Using neurobiological methods, they activated certain regions of the brain in some experimental animals, of which a role in the processing of certain emotions is known. As they report, they were able to artificially trigger the respective emotional facial expressions in this way.
Overall, the study results are now opening up new perspectives in neurobiological research, say the scientists. Because of the possibility of objectively recording emotions, mice can now serve better as a model for examining the nervous processes behind the sensations. “With the computer-aided facial expression analysis we developed, we can now measure the intensity and type of emotion in a split second and compare it with the activity in relevant brain regions,” says Dolensek. His colleague Gogolla adds: “This is an important prerequisite for researching emotions and possible disorders in their processing, such as anxiety disorders or depression.”
Source: Max Planck Institute for Neurobiology, technical article: Science, doi: 10.1126 / science.aaz9468