It is possible to determine which decision-making strategies mice use by observing the subtle facial movements of their snouts. This conclusion was reached by neurobiologists who studied rodents fixed on a treadmill.

Facial Expressions: First Discoveries

In 2020, German scientists discovered that the facial expressions of mice reflect their emotional state. During experiments, the animals were exposed to various stimuli: they were given electric shocks to the tail, fed bitter sugar, and injected with lithium chloride, which induces malaise. By analyzing video recordings of the rodents' reactions, researchers identified six facial expressions corresponding to basic emotions such as fear, disgust, and pleasure.

Facial Movements as Indicators of Thought

A recent study led by Fanny Cazettes from Aix-Marseille University (France) showed that mice's facial movements are not just random actions, but a highly accurate "sensor" of brain activity. For the experiment, mice were fixed on a treadmill and offered a choice between two water dispensers with sweetened water, where the reward would appear or disappear at random.

After a series of unsuccessful attempts, the animals had to decide which dispenser to choose: stay with the current one or switch to the other. The success of their choice depended on the strategy they adopted: some mice focused on the number of failures, while others counted the rewards received. Their facial movements were recorded by a camera at 60 frames per second and then analyzed using mathematical methods to identify hundreds of micro-movement components.

Analyzing Strategies and Cognitive Processes

Over 10 experimental sessions, neurobiologists recorded about 14,000 actions, including licking the dispensers. Of these, 5,877 licks corresponded to the failure-counting strategy, 6,896 to reward-counting, and 1,593 to impulsive decisions. Each movement helped clarify which hidden cognitive process was at play during decision-making and how it was reflected in facial expressions.

Parallel Decisions and Brain Activity

The results, published in the journal Nature Neuroscience, showed that even when a mouse chose one strategy, traces of alternative decisions—simultaneously processed by the brain—could be seen in its facial expressions. For example, when using a failure-based strategy, signs of other options could be detected in the movements of the whiskers and nose area.

By comparing facial data with neuronal activity in different regions of the cerebral cortex (including the supplementary motor, orbitofrontal, and olfactory areas), researchers concluded that facial expressions were as informative as neural activity, and in some cases even more precise. Notably, in the supplementary motor area, information appeared 50 milliseconds earlier than in facial expressions, highlighting its key role in initiating expressions.

Outlook: Diagnosing Through Facial Movements

Thus, neurobiologists have proven that facial movements reflect not only emotions but also complex cognitive processes, including the consideration of alternative options the brain analyzes during decision-making. The ability to "read" thought processes from video recordings opens up prospects for developing non-invasive methods to diagnose mental disorders and neurodegenerative diseases.