Mice form categories to simplify their world. Showing that, researchers identified neurons that encode learned categories.
© MPI of Neurobiology/ Kuhl
Yet another religion-based dogma fell to investigation by science recently. The dogma was that there is something unique about humans that sets us apart from the other animals as some sort of special creation - the basis of our belief that we own the planet and everything on and in it, including the other animals, incidentally.
In particular, humans were once thought to be the only sapient, tool-making species. That dogma has been laid to rest many times with many species now known to be capable of logical reasoning, tool-making and use, and problem-solving.
Now here we have evidence, provided by scientists working at the Max Planck Institute of Neurobiology, Martinsried, Germany, that mice can categorise information and think in the abstract - a fundamental of logical reasoning, information processing and learning, and mice use the same parts of their brain to do it with as we use. Their results were published, open access, in Nature recently.
The Max Plank Gesellschaft news release explains:
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 at the Max Planck Institute of Neurobiology 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.In summary: like humans, mice can categorise information and gradually learn to simplify their surroundings, then use that abstracted information to categorise new information - using the same region of their brain that humans use and the same neurophysiological processes.
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.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?
Sandra Reinert, first author
Max Planck Institute of Neurobiology,
Martinsried, Germany
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.
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.
Pieter Goltstein, senior author
Max Planck Institute of Neurobiology,
Martinsried, GermanyMice categorize surprisingly well
Sandra Reinert and Pieter Goltstein, together with Mark Hübener 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.
The discovery of category-selective neurons in the mouse brain was a key point. It allowed us for the first time to observe the activity of such neurons from the beginning to the end of category learning. This showed that the neurons don't acquire their selectivity immediately, but only gradually develop it during the learning process.And not only that: when the researchers switched the sorting rules, the mice ignored what they had learned before and re-sorted the pictures according to the new rule – something we humans do all the time while learning new things. Therefore, the study demonstrates for the first time to what extent and with which precision mice categorize and thereby approach our capacity for abstraction.
Tobias Bonhoeffer, co-author Max Planck Institute of Neurobiology,
Martinsried, Germany
Neurons gradually develop a category representation
With this insight, the researchers were now able to investigate the basis of categorization in the mouse brain. They focused on the prefrontal cortex, a brain region which in humans is involved in complex thought processes. The investigations revealed that certain neurons in this area become active when the animals sort the striped patterns into categories. Interestingly, different groups of neurons reacted selectively to individual categories.
Tobias Bonhoeffer explains: "The discovery of category-selective neurons in the mouse brain was a key point. It allowed us for the first time to observe the activity of such neurons from the beginning to the end of category learning. This showed that the neurons don't acquire their selectivity immediately, but only gradually develop it during the learning process."
It turns out then that this is not a skill unique to humans but is also present in a mammalian species only distantly related to us. In all probability then this is a characteristic of a mammalian brain, not just of a human brain, and human brains work pretty much like other mammalian brains
The scientist's paper can be read, open access, in Nature:
Yet another example of how beliefs derived from evidence-free religious dogmas are proving to be wrong when investigated by science using real world evidence, illustrating yet again why religions are such poor tools for discovering the truth about the world.Abstract
The ability to categorize sensory stimuli is crucial for an animal’s survival in a complex environment. Memorizing categories instead of individual exemplars enables greater behavioural flexibility and is computationally advantageous. Neurons that show category selectivity have been found in several areas of the mammalian neocortex1,2,3,4, but the prefrontal cortex seems to have a prominent role4,5 in this context. Specifically, in primates that are extensively trained on a categorization task, neurons in the prefrontal cortex rapidly and flexibly represent learned categories6,7. However, how these representations first emerge in naive animals remains unexplored, leaving it unclear whether flexible representations are gradually built up as part of semantic memory or assigned more or less instantly during task execution8,9. Here we investigate the formation of a neuronal category representation throughout the entire learning process by repeatedly imaging individual cells in the mouse medial prefrontal cortex. We show that mice readily learn rule-based categorization and generalize to novel stimuli. Over the course of learning, neurons in the prefrontal cortex display distinct dynamics in acquiring category selectivity and are differentially engaged during a later switch in rules. A subset of neurons selectively and uniquely respond to categories and reflect generalization behaviour. Thus, a category representation in the mouse prefrontal cortex is gradually acquired during learning rather than recruited ad hoc. This gradual process suggests that neurons in the medial prefrontal cortex are part of a specific semantic memory for visual categories.
Reinert, Sandra; Hübener, Mark; Bonhoeffer, Tobias; Goltstein, Pieter M.
Mouse prefrontal cortex represents learned rules for categorization
Nature (2021). DOI: 10.1038/s41586-021-03452-z
Copyright: © 2021. Published by Springer Nature Ltd.
Open access
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
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