The conclusions of the study by the University of Aix-Marseille may be surprising. Based in particular on video, associated with machine learning techniques, neuroscientists analyzed the subtle facial movements of mice which would make it possible to betray, not emotions, but decision-making in the face of a specific situation.
Can facial expressions give an indication of an animal’s “thoughts”? This is the surprising hypothesis of researchers at the University of Aix-Marseille who carried out an experiment on mice. They had to solve a small riddle and, to do this, they had different strategies, betrayed by movements of their faces according to a study published on September 30, 2025 in Nature Neuroscience .
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Neuroscientists have combined several tools. Firstly, video associated with machine learning techniques or machine learning. All supported by the recording of neuronal activity which “allows us to link facial expressions to operations that brain cells are doing at the same time”notes Fanny Cazettes, CNRS researcher and first author of the study. The team also used optogenetics. This technique “uses laser light to inhibit neuronal activity. We will thus alter the facial expressions and behavior of the animal”. Sufficient according to the researchers to rule out parasitic factors from the experiment.
The idea was not to determine emotions but rather “animal cognitive thinking processes”. Concretely, the researchers identified “very subtle movements of the animal linked to precise decision-making”. It seems a priori complicated to associate a movement with an action intention. “What really surprised us was the fact that these thoughts were ‘mapped’ onto the mice’s faces in a very stereotypical way regardless of the individual. »
Transposable to humans?
Fanny Cazettes assures us: in this experiment, “we know exactly what the statistics of the task we are proposing to the mouse are. We record all these variables and, in our mathematical models, we can control whether they produce an effect or not..
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Could this “predictability” be transposable to other animals, or even humans? “We are almost sure of it, especially on primates. Both apes and humans have even more subtle facial expressions than the mouse. » The advantage of the mouse is that it can easily record brain activity to test hypotheses. If, for the moment, researchers have limited themselves to a few actions, the range of interpretable thoughts could quickly expand.
Applied to humans, this less expensive and less invasive method could be of interest in clinical medicine. “We could diagnose mental pathologies that are difficult to characterize, psychiatric disorders such as bipolarity or schizophrenia”says Fanny Cazettes.
But it can also be worrying. Without ethical regulation, it would present a risk to mental privacy. And it could power a social control with “all the cameras there are in the street and even the videos that people post on social networks of their own free will”recognizes the neuroscientist. Researchers have already been contacted by labs working on humans.
