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Biologist Marek Kaczmarzyk talks about how humans differ from chimpanzees, the problem with fractions, ...
2020-10-25 09:00:00

How the Brain Matures
An Interview with Marek Kaczmarzyk

How the Brain Matures

The tricky period of adolescence is not only about raging hormones and intergenerational conflict, but also about structural changes emerging in the brain. Aleksandra Pezda talks to the neuroeducationalist Marek Kaczmarzyk.

Read in 12 minutes

The human brain is born prematurely. In the past, scientists believed that by the time the brain reached six years old, it was pretty much similar in construction and capabilities to an adult brain. Now we know that it reaches maturity only at about the 25th year of life. In truth, it never stops developing. I spoke with the biologist and neuroeducationalist Marek Kaczmarzyk – author of textbooks and co-creator of school syllabuses – about it. His latest book, Strefa Napięć [Tension Zone] addresses the phenomenon of difficult adolescence in light of the latest discoveries in neurology.

Aleksandra Pezda: Neurobiologists today say that the human brain is born prematurely. What does this mean?

Marek Kaczmarzyk: It means that we are born with a brain much less developed than in other mammals and it takes much longer for our species’ brain to develop after birth. Scientists put this phenomenon down to the social functioning of Homo sapiens. While our closest cousins, the chimpanzees, lived and live in groups of about 30-60 individuals, humans gradually increased the size of their groups. In the end, by the time our ancestors had reached an anatomical shape similar to that which we have today, they would create groups of around 150 individuals. In order to function well within such a large group, they needed a brain with greater capabilities. It is believed that our brains began to enlarge over the course of evolution. But everything comes at a cost; a large brain is a problem at birth. How is it possible to force a large skull down through the birth canal and not kill the mother? Biology found a solution: humans are born when their brains are not yet fully mature.

What is the connection between the size of the brain and the formation of large social groups?

As part of a larger social group, a person has to process a larger amount of more complicated information, so that they can get to know other members of the group, find their place within it, and function properly. This is important for us as a species, because we developed an evolutionary advantage, derived precisely from our social activity within the largest groups of animals on the planet. From a biological perspective, a human being is poorly specialized. We don’t have long fangs, can’t run quickly, and nor do we have any great physical strength. No armour, no fur. How do we survive like this? Through culture, understood as the collective product of our minds. Yet we have paid for this with the need to be born prematurely and the consequent development of the brain during the early years of life, including, among other things, the difficult period of adolescence. Teenage problems are, as neurobiology believes today, the consequence of neurodevelopmental processes.

What is the problem with the teenage brain?

At this stage of its development, the brain undergoes a series of dynamic changes. For example, the structure of the cerebral cortex – the so-called grey matter, which holds the group of neurons involved in processing information – changes. First, the number of synapses increases, i.e. the connections that pass impulses between the cells. In our first few years of life, we have twice as many of them as we do as adults. Later on, these connections are pruned, occurring in different parts of the brain at different times. Later still, roughly between the ages of 13 and 18, there is a sharp reduction in the number of synapses in the prefrontal cortex, which is particularly important for behaviour. At the same time, changes take place in the white matter of the brain, which consists of nerve fibres made from so-called myelin sheaths. The presence of myelin facilitates the transmission of nerve impulses. Between 12 and 16 years old, white matter starts to build up, but still, in certain places, there is less than in an adult, which means that the nerve signals in a teenager travel less effectively than they do in adults. Therefore, we have large changes occurring together with limited speed of information transfer. It should be no surprise that this causes a huge upheaval in the nervous system and, as a result, in teenagers’ behaviour. This is why it is hard for us to understand adolescents. All the more so since the very areas of the brain that are being transformed at this time are responsible for rational thought, the consequences of choices and emotions.

If the brain develops with age, why does it prune valuable neural connections?

There are several theories about this, two of which I find convincing. The first suggests that a more complex network of neurons doesn’t help us to process large amounts of information. IT specialists can confirm this – those who work on neural-type IT networks observe that a more complicated network doesn’t actually help effective problem-solving. Complex networks contain large numbers of pathways along which communications can travel, and having a large number of possibilities increases the likelihood of a mistake. In addition, it wastes time. This implies that we get rid of excess neural connections in order to simplify the flow of information and make the network function more smoothly.

The second theory touches on energy expenditure. The brain of a five-year-old uses approximately half the energy that the body has at its disposal. The brain of an adult can only permit itself to expend one quarter of the body’s energy on itself. In other words, an overcomplex brain would use too much energy. Hence the period of tidying up and reducing its complexity.

How does this transformation in the brain translate into the daily experience of teenagers?

Each of us designs our own model of reality for our own use. We try to find our place in the world and answer questions about who we are, what is important for us and what we think about others. This helps us to function within society. Teenagers also work like this. Meanwhile, the structure of their young brains is constantly changing – on Monday their model of the world may have features that will be gone by Friday. What’s important to a teenager today may no longer be so important in a few days’ time. That is why a person at this age wants to be a writer one day and a truck driver the next, with the same level of conviction in both cases. In short, for biological reasons, a teenager may not be able to organize their life systematically. Unfortunately, we cannot explain this by saying that the child is stupid or wayward. Nor should we blame ourselves for mistakes in their upbringing, although such mistakes of course do happen and affect teenagers’ progress. Adolescent difficulties are primarily down to biology and are connected with changes to the structure of the brain.

Is this a new theory?

If we’re talking about breakthroughs in understanding the adolescent brain, among the sources available is the body of research by the paediatric neurologist, Peter R. Huttenlocher – an American scientist of German descent. He was working in the 1960s and 1970s with only an electron microscope at his disposal. This is how it worked: he would put a slide of brain tissue under the microscope, using dye to show up the neural connections. He would count them, one by one. A titanic job, only for the toughest. And Huttenlocher must have been a tough cookie, because he devoted 30 years of his life to this research. He compared samples from some 50 people who had died at different ages; the majority were children, but also some adults. Today we would say that this was a small sample group. Back then, however, there was no other way.

Huttenlocher was the first scientist to notice that something unexpected happens to the brain during adolescence. Earlier it was thought that the brain developed rapidly until the age of four or five, by which time it had more or less attained the structure found in adults, after which we can only make use of the potential it has developed. This was a reasonable conclusion given that, by the age of six, the brain has grown to around 90% of its adult size. However, Huttenlocher demonstrated that something else was going on. He was a pioneer in this field. Only much later on were research techniques able to go deeper and provide insight into the processes, the understanding of which is revolutionizing the science of child development today.

Currently, we can confirm Huttenlocher’s discoveries thanks to new, neuroimaging technologies. We can compare hundreds of human brains at different ages. We set the scanners up to find the neural connections and they count them for us. No longer do we have to sit over a microscope for years on end, nor wait for brain tissue from dead patients.

Since we mature with age, how is it that an eight-year-old boy has good relations with his parents and when he turns 13, in theory he should be ‘more mature’, but instead slams doors and ignores us?

There is a widely-held belief that brain development should take a linear course and deliver an even increase in capabilities. From a neurobiological perspective it looks rather different. Not all parameters develop simultaneously and steadily over time. Sometimes development means regression; some processes decline. For example, the skeleton – first it forms as a cartilage framework and, towards the end of the prenatal period, it is converted into a bone structure. From the perspective of the cartilage development this is obviously a regression, but the cartilage must disappear in order for bone to develop in its place. The brain develops along the same lines. Certain stages of this process must be brought to a close or reversed in order to open the way for subsequent ones.

So teenagers are not rebelling, rather their brains are unable to ‘listen to adults’?

And this brings enormous benefits. While the thing we call intergenerational conflict can be a problem for us, on the other hand, it is the strength of our species. If children were as well-behaved as we wished, our species wouldn’t develop. We would only take advantage of the things that we can do ourselves, which our parents could do or invented, and their parents in turn and so on… all the way back to the origins of our species. We might therefore now be at the same stage of development as our closest cousins, the chimpanzees.

What pulled us away from this friendly group?

In very simple terms, it was the developmental immaturity of our brains. In other words, the very thing that bothers us today about our teenagers. Chimpanzees use a life strategy which is very similar to that of humans. They also create culture, if our definition of culture can include the exchange of information that is adaptively useful through imitation and not through genes. As with humans, chimpanzees learn many things that are passed down from generation to generation. For example, how to get termites out of a termite mound, how to get nuts out of their shells, or how to recognize poisonous plants. There is only one difference – and a fundamental one – between how the next generation of chimpanzees learns and how humans learn. Chimpanzees simply carefully follow the actions and outcomes of the actions of the adults they observe, but generally don’t change the methods used. Young humans, in contrast, look for new ways of doing things, even if adults show them their tried and tested methods.

But why, if imitation is simple, effective and safer?

A young human brain can’t do anything else. Structurally it is not made for simple imitation. Very dynamic changes are happening within it, so it cannot keep up with the continuous assimilation of information. Of course, this can be dangerous and for the adults very trying. It causes social and cultural conflicts and misunderstandings within the family, schools and wider society. Simultaneously it creates an intergenerational added value, because one in 1000 ideas developed by a transforming teenage mind produces a better model for progress than the one employed so far.

There’s no point in giving them advice, because they won’t take it anyway?

Teenagers don’t go to their parents or guardians for advice in order to apply that advice directly. They don’t expect strict instructions. They ask for advice in order to find out the opinion of adults on a specific subject and build up their own strategy, based inter alia on that opinion. This absolutely doesn’t mean that adults should give up showing teenagers their own tried and tested solutions. Quite the opposite – these new solutions need to be based on something.

Changes in brain structure occur in regions of the brain that are key to functions such as planning, anticipating the future, delayed gratification, understanding others and the correct encoding of emotions. Please imagine what can happen when these areas of the brain don’t work so well from time to time. We can see this, for example, in school achievements. At around 12 or 13 years old, children go through a low point in their competences, which most parents and teachers react nervously to – adults interpret this as an unwillingness by the young person to work.

I remember being told as a child: “You’ve lowered your sights.” So this wasn’t my fault?

If you look at the statistics, this is rather typical. Obviously one can pacify children, terrorize and force them to work harder. They will, to a greater or lesser extent, try to achieve the outcomes we want. But the durability and quality of the results obtained this way will be underwhelming. Above all, children cannot exceed in any case the capabilities of the prevailing state of their central nervous systems. For example, it was demonstrated recently that those regions of the brain that are fundamental to working with numbers, abstract things, and those regions of the brain responsible for understanding long chains of cause and effect, only mature after about the age of 10. Before then, most children are unable to perform tasks such as fractions, which seem simple to adults. Things that are so obvious to adults are beyond the grasp of children’s brains. And yet we introduce fractions into the curriculum earlier – we demand this from eight- and nine-year-olds. These children then become convinced that they are rubbish at maths. If we only waited until their brains were more mature, they may turn out to be gifted mathematicians.

And yet some children manage well with maths.

Because some children mature more quickly. And, of course, children differ in their abilities; not every child will be as good at maths as at writing or running. Teachers and parents most often give me the example of fractions. This is no coincidence. After the age of 12, these same children might be very good at maths. If someone classified as weak in mathematics later on engages in projects that require mathematical capabilities, even if this is not explicitly described, it turns out that it doesn’t go any worse for them than for others, but they are just convinced that they can’t do it. The creators of school syllabuses really ought to pay closer attention to neurological research results.

Since the 1950s, educators have instructed us to treat children as ‘ready-made’ people, yet here neurobiology has proven that the teenage brain is extremely immature. How can we reconcile this?

The expectations of educators don’t conflict with the state of neurobiological sciences. We don’t undermine the approach that tells us to think about children as people. On the contrary, we complement this approach. After all, educators don’t instruct us to see children as adults. They only warn us to take children seriously. However, it’s worth knowing – and this is what neurobiology teaches us – that a child is not a small adult and is fundamentally different from an adult. This may prevent us from setting goals that a child is unable to achieve.

When does the brain finally reach maturity?

The brain never finishes developing – it changes throughout our entire lifetime. However, we can identify in which periods particular processes end. For example, the hippocampus, which is necessary for laying down permanent, explicit memories, takes on its structure at around the age of three – this is why we only have explicit memories from that time onwards. This is one stage in the maturing of the brain.

The selection of neural pathways in the cortex of the brain, characteristic for growing up, finishes in certain regions of the cortex only at around 20 or even 25 years old. From this moment on, we can say that common sense trumps emotions and that we are able to plan properly, take completely rational decisions, envisage the consequences of our actions and integrate information. In turn, the process of myelination, which is responsible for the speed and efficiency of interregional connectivity, only finishes at about 45 years old. These, however, are only examples of the end of particular processes. The brain is a system, a whole, which in any given moment is processing information and solving concrete problems. This is how we should view it.

Parts of this interview have been edited and condensed for clarity and brevity.

Marek Kaczmarzyk; illustration by Cyryl Lechowicz
Marek Kaczmarzyk; illustration by Cyryl Lechowicz

Marek Kaczmarczyk:

Doctorate in Biological Sciences, Professor in the Department of Natural Sciences at the University of Silesia. A proponent of evolutionary teaching with the practical use of the influence of evolutionary mechanisms on the processes of learning and teaching. Author of several books, including Szkoła memów [School of Memes], Unikat [Unique Specimen], Biologia wyjątkowości [The Biology of Uniqueness], Szkoła neuronów [School of Neurons], O nastolatkach, kompromisach i wychowaniu, [On Teenagers, Compromise and Upbringing] Strefa napięć [Tension Zone] and Historia naturalna konfliktu z nastolatkiem [The Natural History of Conflict with Teenagers].


Translated from the Polish by Annie Jaroszewicz

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