Categorization is the brain’s tool to organize nearly everything we encounter in our daily lives. Grouping information into categories simplifies our complex world and helps us to react quickly and effectively to new experiences. Scientists have now shown that also mice categorize surprisingly well. The researchers identified neurons encoding learned categories and thereby demonstrated how abstract information is represented at the neuronal level.

A toddler is looking at a new picture book. Suddenly it points to an illustration and shouts ‘chair’. The kid made the right call, but that does not seem particularly noteworthy to us. We recognize all kinds of chairs as ‘chair’ without any difficulty. For a toddler, however, this is an enormous learning process. It must associate the chair pictured in the book with the chairs it already knows — even though they may have different shapes or colors. How does the child do that?

The answer is categorization, a fundamental element of our thinking. Sandra Reinert, first author of the study explains: «Every time a child encounters a chair, it stores the experience. Based on similarities between the chairs, the child’s brain will abstract the properties and functions of chairs by forming the category ‘chair’. This allows the child to later quickly link new chairs to the category and the knowledge it contains.»

Our brain categorizes continuously: not only chairs during childhood, but any information at any given age. What advantage does that give us? Pieter Goltstein, senior author of the study says: «Our brain is trying to find a way to simplify and organize our world. Without categorization, we would not be able to interact with our environment as efficiently as we do.» In other words: We would have to learn for every new chair we encounter that we can sit on it. Categorizing sensory input is therefore essential for us, but the underlying processes in the brain are largely unknown.

Mice categorize surprisingly well

Sandra Reinert and Pieter Goltstein, together with Mark Hubener and Tobias Bonhoeffer, group leader and director at the Max Planck Institute of Neurobiology, studied how the brain stores abstract information like learned categories. Since this is difficult to investigate in humans, the scientists tested whether mice categorize in a way similar to us. To do so, they showed mice different pictures of stripe patterns and gave them a sorting rule. One animal group had to sort the pictures into two categories based on the thickness of the stripes, the other group based on their orientation. The mice were able to learn the respective rule and reliably sorted the patterns into the correct category. After this initial training phase, they even assigned patterns of stripes they had not seen before into the correct categories — just like the child with the new book.

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Materials provided by Max-Planck-Gesellschaft. Note: Content may be edited for style and length.