💭 Scientists read "thoughts" on the face

"Mind reading" evokes images of futuristic scanners, but a study published in Nature Neuroscience demonstrates that a simple video might be enough.

Using machine learning techniques, scientists have shown in mice that facial movements reflect their hidden thoughts. This discovery could offer an unprecedented glimpse into how the brain works, but also signals the need to consider measures to protect private mental life.

Reading thoughts?

It's easy to read emotions on a human face—each has its clear and unambiguous signature. But can we also guess what someone is thinking? A study published in Nature Neuroscience shows that it might be possible, at least in mice. Scientists have shown that their facial movements reveal their thinking strategies. According to them, this is evidence that the content of the mind can be deciphered from simple videos, paving the way for new research and diagnostic tools.

"To our great surprise, we discovered that we could get as much information about what the mouse was 'thinking' as by recording the activity of dozens of neurons," said author Zachary Mainen, a researcher at the Champalimaud Foundation in Portugal. "Having such access to the hidden contents of the mind could represent a major asset for brain research. However, it also highlights the need to start thinking about regulations to protect our private mental life."

What are mice thinking?

In a study published in 2023, the same scientists had presented mice with a small challenge: finding which of two water dispensers provided a sweet reward. Since the correct dispenser changed regularly, the mice had to develop strategies to make the right choice.

"We knew that mice could solve this task using different strategies, and we could identify the strategy used by observing their behavior," explains Fanny Cazettes, first author of the study and now a research fellow at the National Center for Scientific Research and Aix-Marseille University. "We expected that neurons in the mice's brains would only reflect the strategy they were using, but in fact, all strategies were present simultaneously, regardless of which one the mouse was using at that moment."

This discovery led the team to ask a new question: could these strategies visible in the brain also be reflected on the face?

The face, mirror of the mind

To verify this, the scientists recorded the animals' facial movements alongside neural activity in their brains, then analyzed this data using machine learning algorithms. The results are striking: facial movements were just as informative as recording populations of neurons.

"The most surprising thing is that the same expressions corresponded to the same strategies in different mice," emphasizes Davide Reato, co-author of the study, a researcher at Aix-Marseille University and Mines Saint-Étienne.

"This suggests that certain thought patterns translate into stereotypical facial expressions, much like emotions."

A new way to study the brain

For scientists, these results pave the way for non-invasive methods of studying the brain, allowing for a better understanding of its functioning in animals, and perhaps one day in humans. But this advance also raises ethical questions: in a world where cameras are everywhere, how do we protect our private mental life?

"Our study shows that videos are not just recordings of behaviors—they can also offer a detailed window into brain activity. Even though this is exciting from a scientific perspective, it also raises questions about the need to protect our privacy," concluded Alfonso Renart, study author and researcher at the Champalimaud Foundation in Portugal.

Original text by Liad Hollender, independent science writer and content creator, revised by Daniel Boujard, scientific delegate at CNRS Biology.