Cerebellum prevents mouse brain overload

On a quiet summer evening, you can be startled by a loud bang, but the same sound won’t surprise you during a fireworks show. It is the cerebellum that filters these kinds of signals and places them in context, neuroscientists at Erasmus MC discovered. At least, in mice it does.

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Purkinje cells traces
The scientists registered the activity of individual Purkinje cells

All day long your brain is filtering images, smells, sounds and tastes. What is relevant and what is not? Without this filter, you would go completely crazy. Researchers at Erasmus MC’s Neuroscience department have now discovered how the cerebellum of mice helps to separate important signals from less important ones.

Lorenzo Bina

The key appears to lie with what one of the lead researchers Laurens Bosman calls ‘Barbapapa cells’. These cells, with the official name Purkinje cells, are found in the cerebellum of both mice and humans. Bosman and his colleagues taught mice to ignore a loud noise and to respond to a gentle touch of the whiskers. When the mice reacted correctly, they were rewarded with water.

Meanwhile, the researchers recorded what was happening in individual cerebellar Purkinje cells, they write in the scientific journal Cell Reports. PhD student Lorenzo Bina did the lion’s share of the experiments.

Barabapapa cells

The Purkinje cells appeared to change identity. At first, they responded only to loud noise and later only to touch. ‘A kind of Barbapapa cells, in other words,’ says Bosman. The change in the cells kept pace with the learning curve of the mice. The better the mice learned to perform the task, the greater the change in Purkinje cell activity.

Purkinje cells (in red) are located in the cerebellum of mouse and men | Image by Z. Gao

In conclusion, the shapeshifting of the Purkinje cells causes the mice to stop responding to the irrelevant loud noise and instead respond to the relevant touch. Scientists call this selective attention. ‘Everything in this process depends on the context. A loud bang, such as one that startles you on a quiet summer evening, is nothing special during a fireworks show. Selective attention involves reacting not so much to what’s loudest or brightest, but matching your reaction to your expectation,’ Bosman explains.

Born without cerebellum

Mice with dysfunctional Purkinje cells could also learn to ignore the loud noise, but needed more time to do so. Bosman says: ‘We see something similar in people who are born without a cerebellum – something that rarely happens. These people eventually learn to walk, but this can take ten or even twenty years. As a result, we already knew that the cerebellum is important in learning movements, but apparently it works the same way in other forms of learning.’

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