Surprise! – How the brain learns to deal with the unexpected

For children, the world is full of surprises. Hardly anything surprises adults anymore. It sounds obvious, but there are complex processes behind it: Researchers at the University of Basel have decoded how the reaction to the unexpected develops in the growing brain in mice.

How exactly “surprise” is processed in the brain changes as we grow up: unusual stimuli end up in categories like “important” or “uninteresting” much more quickly and are significantly less surprising the second and third time they appear. This increased efficiency makes perfect sense: new stimuli attract attention, but do not trigger an unnecessarily strong reaction that would cost energy. What initially seems trivial has hardly been researched at the level of brain development.

Through experiments with young mice, a team led by neuroscientist Prof. Dr. Tania Barkat has now decoded to some extent how the brain processes surprising sounds and what changes as we grow up. The researchers from the Department of Biomedicine at the University of Basel report their results in the specialist journal “Science Advances”.
Weird tones

In their experiments, the researchers used tone sequences in which a different tone appeared at irregular intervals between identical tones. At the same time, they recorded the animals’ brain waves. Experts call the test the “oddball paradigm” and use it in humans, among other things, to diagnose schizophrenia.

Using such measurements, the researchers were able to understand how the reaction of different brain regions in the young mice to the different tone changed over time. This reaction was initially very strong, but decreased as the respective brain region matured – down to a level known from measurements in adult animals. However, in the various noise processing control centers, this development does not take place simultaneously, but rather with a time delay.

A region called the inferior colliculi, which lies at the beginning of the path from the auditory nerve to the auditory cortex, was fully mature in the animals by the age of 20 days – the earliest point in time that the team examined. A second switching station, the auditory thalamus, only showed an “adult” reaction to the different tone at the age of 30 days.

Development in the cerebral cortex itself, in the so-called primary auditory cortex, took even longer, namely until the 50th day of life. “This development of the surprise reaction begins in the periphery and ends in the cerebral cortex,” summarizes study leader Tania Barkat. The cerebral cortex therefore matures much later than expected. In human years, this would roughly correspond to an age in the early 20s. Without experiences, there is no development

Another observation by the researchers: Experiences play an essential role in this final stage – the development of the surprise reaction in the cerebral cortex. When they raised the mice in a noise-neutral environment, the processing of unexpected sounds in the auditory cortex developed significantly delayed.

A possible explanation for this: The brain – and especially the cerebral cortex – forms an internal picture of the world based on experiences while growing up, with which it compares external stimuli. Anything that doesn’t fit with this “world view” is a surprise, but may also result in an update of the world view.

“However, without experience with noise, the cerebral cortex of these mice cannot develop such a model of the world,”

says neuroscientist Barkat. Accordingly, the classification of tones into “familiar” and “unexpected” does not work correctly.

• Research Group Prof. Dr. Tania Barkat

Source: Angelika Jacobs , University of Basel, Jan 4, 2024