Brain maturation with time

If we think about geniuses, one characteristic that is usually highlighted is their precocity. Mozart was able to play the piano at the age of 4, Einstein wrote his famous theory of special relativity when he was 26, and a 19-year-old Mark Zuckerberg came up with the multimillionaire idea of Facebook. Does this mean that intelligence peaks at a young age? Do all our abilities deteriorate as we grow older? Let’s start our journey by following how the brain changes across life.

When babies are born, most of their organs are already formed and functional, however, there is one that remains as a “work in progress”: the brain. During the first years of an infant, each neuron forms more than one million connections per second. Those contacts are what make our brain function. Early childhood is a period for neurons to explore and make as many connections as possible, yet, we cannot maintain all of them.

Connections that are used more often become stronger, while the ones that are not employed are eventually eliminated. In this manner, communication becomes more efficient. This is a key point because brain cells have to constantly talk to each other. Different brain regions are responsible for distinct abilities. Our survival depends on them interchanging information quickly.

For instance, seeing a lion in the wild activates a brain structure that detects threats, this region communicates with other areas that control motor functions and tell you: fly, you fool! As you can imagine, the faster this happens, the better chances of escaping you have. But this is not only important in life or death situations. Our thoughts, plans, problem-solving, or learning capacities also depend on the effective communication of neurons.

Something so precious has to be protected, the connections that remain are reinforced thanks to the so-called myelin. Myelin is an insulating layer that wraps around neuronal projections as an insulator around a cable. With this molecule, neurons are more resistant and their electrical signals travel quicker. Myelin appears gradually as kids grow enhancing brain function.

To perceive its effect, scientists have developed tests in which they measure the time you take to respond. Imagine that you see an object from a weird perspective, for example, a spoon positioned like the one in the image. To recognize it, our brain has to use different areas. The more myelin we have, the faster those regions communicate, taking less time to respond. 

Extracted from Baird et al., 2005

Both myelination and neuronal connections increase brain volume until around age 40, then it slowly shrinks as tissue starts to degenerate. However, not every part of the brain changes at the same time. The areas that take more time to mature, are the ones that deteriorate first.

The biggest losses already start in our 30s and occur in the prefrontal cortex –important for attention, planning, reasoning, problem solving– and the hippocampus –implicated in learning, memory, and navigation-. But how are these changes translated into our intelligence? Is there no hope for us after our twenties?

Brain structures by ages

Evolution of cognitive functions 

As we get older, we certainly feel that our capacities decrease. However, if you were to undergo major surgery, who would you choose to perform it: a medical student fresh out of college –with a super myelinated brain– or a surgeon with years of experience behind the knife?

Exactly, our answer here tells us that it is not as simple as saying that younger people are smarter. Recent studies suggest that not only is there no peak for our intelligence, but there is no life period at which all our capacities are at their best. Short-term memory for family stories, for instance, begins to decline already by the end of high school, abstract reasoning reaches its top performance in early adulthood and starts to deteriorate after our 30s. What is more, vocabulary and general information do not reach their full potential until past our 40th birthday.

How is that possible? You might wonder. Well, our intelligence is not homogeneous, it can be divided into two different types. The first one is called fluid intelligence and represents our capacity to solve novel problems. This is the one that actually diminishes with time, explaining why it is difficult for older people to learn how to use a new piece of technology such as a smartphone. This type of intelligence is also required for abstract reasoning, hence, puzzles and mathematical problems become more and more challenging as we age. 

In contrast, we find crystallized intelligence, which is the accumulation of knowledge and skills over a lifetime. This second kind of intelligence requires experience, so it increases as we grow older. It includes history knowledge –or/and Star Wars facts, depending on the person– but also implies the ability to interact with our environment. If we have faced a problem many times, we will become very good at solving it.

IQ tests preferentially evaluate fluid intelligence, leading to the idea that young people are smarter. Yet, if we evaluate the performances of 18-27 versus 60-80 year-old people in everyday problems –such as work-related issues or family conflicts– senior citizens beat Gen Z up.

The same happens when we talk about domain-specific expertise. Middle-aged surgeons have confronted different types of problems throughout their practice, accumulating a wide range of tools for visualizing and implementing solutions to the more common complications. In the words of one of the authors of the study “knowledge does not compensate for a declining adult intelligence; it is intelligence!”. But what is this concept of compensation?

Compensation in the aging brain

The brain is not a static organ, it can adapt to changes to maintain our capacities. And this becomes crucial when we talk about aging. In a way, we can see the brain as a system that is able to “fight back” age-related deterioration. A clear example is found when we think about following a route. Visualize the path from your house to the supermarket. No matter if you are 20 or 60, you could do it with your eyes closed.

Nevertheless, if they start construction works and close the street you normally go through, the young and the elderly will react differently. A 20-year-old brain has a map of the surroundings and will picture an alternative path quickly. The person in his 60s, however, has automatized the sequence of movements “I go to the left until the end of the street, then I turn right…”. Hence, it would be harder for the senior citizen to reach the supermarket, as we have ruined her/his cognitive strategy. 

Why different strategies for the same objective? The representation of a map depends on the hippocampus –as we said at the beginning, one of the structures more affected by age– whereas the automatization of movements relies on another brain region that suffers less remodeling.

Changing the brain area to the one that remains in better shape allows us to reach the supermarket despite hippocampal degeneration. Importantly, we do not detect differences unless the road changes, so even though the hippocampal strategy is more flexible, the independent one will work in the most common scenarios. 

To make things clear, the brain is constantly transforming, reaching consecutive peaks for different cognitive skills across life. Even when certain regions start to deteriorate, their functions can be compensated to perform everyday activities. It is true that young people are more prepared for a changing environment, which makes sense, for a kid everything is new and there is so much to learn! As we grow older, energy seems to focus on taking advantage of experience and acquiring expertise.

Fear no more

The good news is that synapse and myelination are influenced by experience. This means that circuits are reinforced by repeated use. Independently of the educational background, mentally stimulating activities, such as reading, writing, or doing crosswords help to reverse cognitive decline.

Moreover, if you like listening to music it’s your lucky day! Researchers have found that this hobby may sharpen the brain’s ability to anticipate events and stay focused. Finally, it does not come as a surprise that social interaction positively influences cognition, just try to picture all the required elements: face recognition, attention, memory…The message is: stay mentally active!

The brain is a plastic organ that never stops changing, contrary to what was usually thought, that transformation is not just deterioration with time. After all, remember that Cervantes published “El Quijote” when he was 58, Darwin’s “On the origin of species” was released when he was 50, and Reagan first came onto the political stage at age 53. Intellectual achievements are not restricted to young people!