Scientists read mice’s ‘thoughts’ from their faces

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Summary: “Mind reading” evokes images of futuristic scanners, but a study published in Nature Neuroscience demonstrates that a simple video may be enough. Using machine learning techniques, a team at the Champalimaud Foundation in Portugal, showed that mice’s facial movements reflect their hidden thoughts. According to the authors, this discovery could offer unprecedented insight into brain function, but also signals a need to consider safeguards for mental privacy.

It’s easy to read emotions on people’s faces – each one has its clear, unmistakable signature. But what about thoughts? A study published in Nature Neuroscience shows that mice’s problem-solving strategies can be deciphered from subtle facial movements. According to the authors, this is a proof of concept that the contents of the mind can be read out from video recordings, potentially offering powerful new research and diagnostic tools.   

“To our surprise, we found that we can get as much information about what the mouse was ‘thinking’ as we could from recording the activity of dozens of neurons,” said author Zachary Mainen, a principal investigator at the Champalimaud Foundation in Portugal. “Having such easy access to the hidden contents of the mind could provide an important boost to brain research. However, it also highlights a need to start thinking about regulations to protect our mental privacy.”

What do mice think about?

In a study published in 2023, the team had challenged mice with a puzzle in which they had to figure out which of two water spouts provided a sugary reward. Since the availability of the reward switched from one spout to the other, the mice had to develop strategies for deciding which spout to opt for.

“We knew that mice can solve this task using different strategies, and we could identify which strategy they were using according to their behaviour,” explained Fanny Cazettes, the first author and now a principal investigator at the Centre National de la Recherche Scientifique and Aix Marseille University. “We expected that neurons in the mice’s brains would only reflect the strategy they used, but in fact all strategies were present simultaneously, regardless of which the mouse was using at the time.”

This discovery presented the team with a unique opportunity to link brain activity and facial movements.  They asked: “Could all strategies simultaneously present in the brain also be detected in the face?”

The mirror of the mind

The team recorded the animals’ facial movements along with the activity of neurons in their brains and analysed these data using machine learning algorithms. The results were striking – the movements of the face were just as informative as populations of neurons.   

Co-author Davide Reato, currently a research associate at Aix Marseille University and Mines Saint-Etienne highlighted that even though these results were remarkably robust, the similarity across mice was even more surprising. “Similar facial patterns represented the same strategies across different mice. This suggests that the reflection of specific patterns of thought at the level of facial movement might be stereotyped, much like emotions.”

A new way of studying the brain

According to the authors, this study charts a path to studying the brain non-invasively, which could help us better understand brain function in health and disease. However, given the ubiquitous nature of video recordings in our society, they also highlight the need to consider how to protect people’s mental privacy. 

“Our study shows that videos are not just records of behaviour – they can also provide a detailed window into brain activity. Even though this is exciting from a scientific perspective, it also raises questions about the need to safeguard our privacy,” concluded author Alfonso Renart, a principal investigator at the Champalimaud Foundation.

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