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MATURING BRAIN: why we’re losing the ability to be surprised

MATURING BRAIN: why we're losing the ability to be surprised
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Angelika Lomako. Barberry, 2023 / Facebook, «Sil-Sol»

 

Have you ever wondered why most people lose the ability to be surprised when they become adults? If not, Swiss scientists from the University of Basel have done it for you and published the results of their study in the journal Science Advances.

It turns out that the «maturation» of the brain is a process as a result of which it learns to evaluate «surprises» without losing energy. Therefore, the nature of how children process «surprises» in their brains changes as they get older.

 

A child is not frightened by something

that he’s patiently preparing the old man in him.

He’s a child, and he’s playing

his childish games

 

Antoine de Saint-Exupéry

 

AMAZEMENT IS A REACTION TO THE UNEXPECTED

 

Almost from birth, babies know how to be genuinely surprised by the simplest things. For example, in the play «peek-a-boo», when someone’s face appears out of the suddenly spread palms. Children can spend hours playing hide and seek, playing catch-up, exploring new spaces, and inventing new games.

Unlike children, adults are much less impressionable — they require a much more substantial emotional impact to respond emotionally. Apparently, the difference in the ability to be amazed between children and adults lies in the difference in the brain’s response to surprise.

Scientists have found that even behind such a seemingly familiar and well-known emotion as surprise, there are very complex and still poorly understood processes. To shed light on this mystery, researchers from the University of Basel decided to use mice and study how their brains cope with unexpected information and events.

 

MICE ALSO LOSE THE ABILITY TO BE SURPRISED

 

Experiments on young mice conducted by a research team led by neuroscientist Tania Barkat help to understand how the developing brain processes unusual, surprising new sounds. And also track changes in its responses as the body matures.

In their research, scientists used an experimental design called the «Oddball Paradigm». Its meaning is a sequence of repetitive incentives, in this case — sound signals. Periodically, the researchers interrupted these signals with another «deviant» stimulus and recorded the reaction of the participant’s mouse brain to this «strange» sound.

Using such measurements, Barkat and her colleagues were able to understand how the response of different brain regions changed over time in young mice due to the variation in the pitch of the sound. Initially, this response was very strong. However, it decreased as the relevant brain region matured to a level comparable to measurements in adult animals.

 

THE BRAIN MATURES UNEVENLY

 

You heard me! The brain does not grow up together or in parallel with us, at least not whole. Its maturation is a complex and non-linear process. For example, not one but several brain regions are involved in sound processing at the same time, but the development of these regions is not simultaneous.

Scientists first looked at an area known as the inferior tubercle — it is located at the beginning of the path from the auditory nerve to the auditory cortex. In mice that were 20 days old, it was already fully mature. At first, Barkat didn’t pay much attention to this.

 

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But what was her surprise when she compared the inferior tubercle with the development of another area — the auditory thalamus. The latter showed an «adult» response to the second «deviant» sound stimulus only when the test mouse was 30 days old.

The development of the cerebral cortex itself, the primary auditory cortex, took even longer — it occurred up to day 50. «The development of the surprise response begins in the periphery and ends in the cortex», says Barkat.

Therefore, the cortex matures much later than scientists originally expected. If you extrapolate the age of a mouse to the age of a human, the rodent’s 50 days would roughly correspond to a human’s 20 years.

 

SURPRISE AS NOT MATCHING THE «WORLDVIEW»

 

The scientists also note that experiences play a crucial role in the development of the surprise response in the cerebral cortex. If the mice were raised in a silent environment, the processing of unexpected sounds was significantly delayed in the auditory cortex.

One possible explanation is that the brain, and in particular its cortex, forms an «internal image of the world» during growth. The brain then matches this internal image with external incentives. Anything that, in one way or another, does not correspond to this «worldview» is perceived by the brain as a surprise.

But over time, this repeated surprise may cease to be a «surprise and entail an adjustment in the internal image of the world. «However, without experience with sounds, the cerebral cortex of these mice is unable to develop such a model of the world», says Barkat. As a result, the animal cannot correctly categorize sounds into «familiar» and «unexpected». It turns out that without experience, there is no development, and with experience, there is no surprise.

 

EXPERIENCE — IS THE BRAIN TIRED OF AMAZEMENT?

 

Why is something that for children is a delightful novelty and extravagant surprise that an adult is never, usually, so fascinated by? The fact is that as we grow older, the nature of how the brain processes information that is new to it changes.

In childhood, any unusual incentive is much more readily and quickly categorized by the brain as «important». «Uninteresting» for us, they become when they are repeated. It seems that this particular feature of the brain is called «experience» and «worldly wisdom».

Its meaning can be most accurately expressed in the words of the biblical Ecclesiastes: «What has been will be again, and what has been done will be done again; there is nothing new under the sun. Is there a case where one can say, «Look, this is new»; It has already existed in the ages before us» (Eccl. 1;9, 1:10).

It is no coincidence that these words are spoken in the Bible by King Solomon, who is considered the wisest man who ever lived on earth. The same can be said about the Sumerian hero of the first epic in the history of mankind — Gilgamesh, who in the Akkadian language was called «the one who has seen everything».

And the point here is not at all in the psychological peculiarities of Middle Eastern cultures but in the natural processes occurring in the human brain. Unusual triggers lose their influence on the brain after they are repeated for the second, third, fourth time…

The brain does not find it necessary to respond to repeated incentives with strong emotional reactions: constant surprise costs it a lot of additional and, most importantly, completely unnecessary energy expenditure.

 

Original study: Sequential maturation of stimulus-specific adaptation in the mouse lemniscal auditory system

 


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