Summary: Researchers studied mice to understand how the brain processes unexpected stimuli during development.
They found that the brain’s response to surprises changes as we grow, becoming more efficient in categorizing stimuli as “important” or “uninteresting.” This developmental change helps conserve energy by reducing excessive reactions to familiar surprises.
The study also revealed that the brain regions responsible for processing surprises mature at different rates, with the cerebral cortex maturing later, akin to the early 20s in human years. Experience with sounds plays a crucial role in this development.
Key Facts:
- Brain responses to surprising stimuli become more efficient as we grow, conserving energy.
- Different brain regions mature at varying rates when processing surprises.
- Experience with sounds is essential for the development of the surprise response in the cerebral cortex.
Source: University of Basel
For children, the world is full of surprises. Adults, on the other hand, are much more difficult to surprise. And there are complex processes behind this apparently straightforward state of affairs. Researchers at the University of Basel have been using mice to decode how reactions to the unexpected develop in the growing brain.
Babies love playing peekaboo, continuing to react even on the tenth sudden appearance of their partner in the game. Recognizing the unexpected is an important cognitive ability. After all, new can also mean dangerous.
The exact way in which surprises are processed in the brain changes as we grow, however: unusual stimuli are much more quickly categorized as “important” or “uninteresting”, and are significantly less surprising the second and third time they appear.
This increased efficiency makes perfect sense: new stimuli may gain our attention, but do not cause an unnecessarily strong reaction that costs us energy. While this may appear trivial at first, so far there has been very little research into this fact in the context of brain development.
Experiments with young mice conducted by Professor Tania Barkat’s research team have now begun to decode how the developing brain processes surprising sounds and what changes as we grow up.
The researchers have reported on their findings in the journal Science Advances.
Strange sounds
In their experiments, the researchers used sequences of sounds in which a different tone was heard at irregular intervals in between a series of identical ones. At the same time, they recorded the animals’ brain waves. This process is known as the “oddball paradigm”, and is used by health professionals for purposes such as the diagnosis of schizophrenia.
Using these measurements, the researchers were able to understand how the reaction of different brain regions to the change of tone developed over time in the young mice. This reaction was initially very strong, but decreased as the relevant brain region matured, to a level comparable to that of measurements in adult animals. This development does not take place simultaneously in the various areas of the brain that process sound, however.
A region known as the inferior colliculus, located at the beginning of the path from the auditory nerve to the auditory cortex, was already fully mature in the animals at the age of 20 days, the earliest point in time studied by the team. A second site, the auditory thalamus, only showed an “adult” reaction to the differing tone at the age of 30 days.
Development in the cerebral cortex itself, the “primary auditory cortex”, took even longer, until day 50.
“This development of the surprise reaction thus begins in the periphery and ends in the cerebral cortex,” says study leader Tania Barkat.
The cerebral cortex therefore matures much later than expected – in human years, this would equate roughly to the early 20s.
No development without experience
The researchers also observed that experiences play a key role in the development of the surprise response in the cerebral cortex. If the mice were reared in a noise-neutral environment, the processing of unexpected sounds in the auditory cortex was significantly delayed.
One possible explanation for this is that the brain – and the cerebral cortex in particular – forms an internal image of the world during growth, which it then compares with external stimuli. Anything that does not correspond to this “worldview” is a surprise, but may also result in an update.
“Without experience with sounds, however, the cerebral cortex in these mice is unable to develop such a model of the world,” says neuroscientist Barkat. As a result, the animal is unable to categorize sounds properly into “familiar” and “unexpected.”
About this neurodevelopment research news
Author: Reto Caluori
Source: University of Basel
Contact: Reto Caluori – University of Basel
Image: The image is credited to Neuroscience News
Original Research: Open access.
“Sequential maturation of stimulus-specific adaptation in the mouse lemniscal auditory system” by Tania Barkat et al. Science Advances
Abstract
Sequential maturation of stimulus-specific adaptation in the mouse lemniscal auditory system
Stimulus-specific adaptation (SSA), the reduction of neural activity to a common stimulus that does not generalize to other, rare stimuli, is an essential property of our brain. Although well characterized in adults, it is still unknown how it develops during adolescence and what neuronal circuits are involved.
Using in vivo electrophysiology and optogenetics in the lemniscal pathway of the mouse auditory system, we observed SSA to be stable from postnatal day 20 (P20) in the inferior colliculus, to develop until P30 in the auditory thalamus and even later in the primary auditory cortex (A1).
We found this maturation process to be experience-dependent in A1 but not in thalamus and to be related to alterations in deep but not input layers of A1. We also identified corticothalamic projections to be implicated in thalamic SSA development.
Together, our results reveal different circuits underlying the sequential SSA maturation and provide a unique perspective to understand predictive coding and surprise across sensory systems.
