Intelligence: from genetics to "wires" and "processor" of the human brain

2024 Author: Seth Attwood | [email protected]. Last modified: 2023-12-16 15:55

Why are some people smarter than others? Since time immemorial, scientists have been trying to figure out what to do to keep the head clear. Referring to a number of scientific studies, Spektrum discusses the components of intelligence - from genetics to the "wires" and "processor" of the human brain.

Why are some people smarter than others? Since time immemorial, scientists have been trying to figure out what needs to be done in order for the head to think well. But now it's at least clear: the list of components of intelligence is longer than expected.

In October 2018, Wenzel Grüs showed something incredible to millions of TV viewers: a student from the small German town of Lastrut hit a soccer ball with his head more than fifty times in a row, never dropping or picking it up with his hands. But the fact that the audience of the Russian TV show "Amazing People" awarded him with enthusiastic applause was explained not only by the young man's athletic dexterity. The fact is that, playing the ball, he in between times raised the number 67 to the fifth power, having received a ten-digit result in just 60 seconds.

Wenzel, who is 17 today, has a unique mathematical gift: he multiplies, divides, and extracts roots from twelve-digit numbers without a pen, paper or other aids. At the last world championship in oral counting, he took third place. As he himself says, it takes him from 50 to 60 minutes to solve especially difficult mathematical problems: for example, when he needs to factor a twenty-digit number into prime factors. How does he do it? Probably, his short-term memory plays the main role here.

It is clear that Wenzel's brain is somewhat superior to the thinking organ of his normally gifted peers. At least when it comes to numbers. But why, in general, do some people have greater mental capacity than others? This question was still on the mind of British nature researcher Francis Galton 150 years ago. At the same time, he drew attention to the fact that often differences in intelligence are associated with the origin of a person. In his work Hereditary Genius, he concludes that human intelligence can be inherited.

Multi-Ingredient Cocktail

As it turned out later, this thesis of his was correct - at least in part. American psychologists Thomas Bouchard and Matthew McGue analyzed more than 100 published studies of the similarity of intelligence among members of the same family. In some works, identical twins have been described, separated immediately after birth. Despite this, on intelligence tests, they showed almost the same results. The twins who grew up together were even more similar in terms of mental abilities. Probably, the environment also had an important influence on them.

Today, scientists believe that 50-60% of intelligence is inherited. In other words, the difference in IQ between two people is a good half due to the structure of their DNA received from their parents.

In search of genes for intelligence

However, the search for the hereditary materials specifically responsible for this has so far led to little. True, sometimes they found some elements that at first glance were related to intelligence. But upon closer inspection, this relationship turned out to be false. A paradoxical situation arose: on the one hand, countless studies proved a high hereditary component of intelligence. On the other hand, no one could tell which genes were specifically responsible for this.

Recently, the picture has changed somewhat, primarily due to technological progress. The construction plan of each individual is contained in his DNA - a kind of giant encyclopedia, consisting of approximately 3 billion letters. Unfortunately, it is written in a language that we hardly know. Although we can read the letters, the meaning of the texts of this encyclopedia remains hidden from us. Even if scientists succeed in sequencing the entire DNA of a person, they do not know which parts of it are responsible for his mental abilities.

Intelligence and IQ

The word intellect comes from the Latin noun intellectus, which can be translated as "perception", "understanding", "understanding", "reason" or "mind". Psychologists understand intelligence as a general mental ability that encompasses various competencies: for example, the ability to solve problems, understand complex ideas, think abstractly, and learn from experience.

Intelligence is usually not limited to one subject, such as mathematics. Someone who is good in one area often excels in others. Talent clearly limited to one subject are rare. Therefore, many scientists proceed from the fact that there is a general factor of intelligence, the so-called factor G.

Anyone who is going to study intelligence needs a method to measure it objectively. The first intelligence test was developed by French psychologists Alfred Binet and Théodore Simon. They used it for the first time in 1904 to assess the intellectual abilities of schoolchildren. On the basis of the tasks developed for this purpose, they created the so-called "Binet-Simon scale of mental development." With its help, they determined the age of the child's intellectual development. It corresponded to a number on a scale of problems that the child could completely solve.

In 1912, the German psychologist William Stern proposed a new method in which the age of intellectual development was divided by the chronological age, and the resulting value was called the intelligence quotient (IQ). And although the name has survived to this day, today IQ no longer describes age ratios. Instead, IQ gives an idea of how the level of intelligence of an individual correlates with the level of intelligence of the average person.

People differ from each other, and accordingly their sets of DNA differ. However, individuals with high IQs must match at least those parts of DNA that are associated with intelligence. Scientists today proceed from this fundamental thesis. By comparing the DNA of hundreds of thousands of test subjects in millions of parts, scientists can identify the hereditary regions that contribute to the formation of higher intellectual abilities.

A number of similar studies have been published in recent years. Thanks to these analyzes, the picture becomes increasingly clear: special mental abilities depend not only on hereditary data, but on thousands of different genes. And each of them makes only a tiny contribution to the phenomenon of intelligence, sometimes only a few hundredths of a percent. “It is now believed that two-thirds of all human variable genes are directly or indirectly associated with brain development and thus potentially with intelligence,” emphasizes Lars Penke, professor of biological personality psychology at Georg August University in Göttingen.

Seven Sealed Mystery

But there is still one big problem: today there are 2,000 known places (loci) in the structure of DNA that are associated with intelligence. But in many cases it is not yet clear what exactly these loci are responsible for. To solve this puzzle, intelligence researchers observe which cells are more likely than others to respond to new information. This may mean that these cells are in some way connected with thinking abilities.

At the same time, scientists are constantly faced with a certain group of neurons - the so-called pyramidal cells. They grow in the cerebral cortex, that is, in that outer shell of the brain and cerebellum, which experts call the cortex. It contains mainly nerve cells that give it its characteristic gray color, which is why it is called "gray matter".

Perhaps pyramidal cells play a key role in the formation of intelligence. This is indicated, in any case, by the results of studies carried out by the neurobiologist Natalia Goryunova, professor at the Free University of Amsterdam.

Recently, Goryunova published the results of a study that attracted everyone's attention: she compared pyramidal cells in subjects with different intellectual abilities. Tissue samples were taken mainly from material obtained during operations on patients with epilepsy. In severe cases, neurosurgeons try to remove the focus of dangerous seizures. In doing so, they always remove parts of healthy brain material. It was this material that Goryunova studied.

She first tested how the pyramidal cells contained in it react to electrical impulses. She then cut each sample into thinnest slices, photographed them under a microscope and assembled them again on the computer into a three-dimensional image. Thus, she, for example, established the length of dendrites - branched outgrowths of cells, with the help of which they pick up electrical signals. “At the same time, we established a connection with the IQ of the patients,” explains Goryunova. "The longer and more branchy the dendrites were, the smarter the individual was."

The researcher explained this very simply: long, branched dendrites can make more contacts with other cells, that is, they receive more information that they can process. Added to this is another factor: “Due to the strong branching, they can simultaneously process different information in different branches,” emphasizes Goryunova. Due to this parallel processing, cells have great computational potential. “They work faster and more productively,” Goryunova concludes.

Only part of the truth

No matter how convincing this thesis may seem, it cannot be considered fully proven, as the researcher herself frankly admits. The fact is that the tissue samples she examined were taken mainly from one very limited area in the temporal lobes. Most epileptic seizures occur there, and therefore, as a rule, surgery for epilepsy is performed in this area. “We cannot yet say how things are in other parts of the brain,” Goryunova admits. "But new, yet unpublished research results from our group show, for example, that the relationship between dendrite length and intelligence is stronger in the left side of the brain than in the right."

It is still impossible to draw any general conclusions from the research results of the Amsterdam scientists. Moreover, there is evidence that speaks of the exact opposite. They were obtained by Erhan Genç, a biopsychologist from Bochum. In 2018, he and his colleagues also investigated how the structure of gray matter differs between very smart and less intelligent people. At the same time, he came to the conclusion that the strong branching of dendrites is more harmful than conducive to thinking ability.

True, Gench did not examine individual pyramidal cells, but placed his subjects in a brain scanner. In principle, magnetic resonance imaging is not suitable for examining the finest fiber structures - the resolution of the images, as a rule, turns out to be insufficient. But the Bochum scientists used a special method to see the direction of diffusion of tissue fluid.

Dendrites become barriers to fluid. By analyzing diffusion, it is possible to determine in which direction the dendrites are located, how branched they are, and how close they are to each other. Result: in smarter people, the dendrites of individual nerve cells are not so dense and do not tend to disintegrate into thin "wires". This observation is diametrically opposed to the conclusions made by the neuroscientist Natalia Goryunova.

But don't pyramidal cells need a variety of external information to perform their tasks in the brain? How is this consistent with the low degree of branching identified? Gench also considers the connection between cells to be important, but in his opinion, this connection should have a purpose. “If you want the tree to bear more fruit, cut off the extra branches,” he explains. - The same is the case with synaptic connections between neurons: when we are born, we have a lot of them. But in the course of our life we thin them out and leave only those that are important to us."

Presumably, it is thanks to this that we can process information more efficiently.

The "living calculator" Wenzel Grüs does the same, turning off everything around him when solving a problem. Processing background stimuli would be counterproductive to him at this point.

Indeed, people with rich intelligence show more focused brain activity than less gifted people when they have to solve a complex problem. In addition, their thinking organ requires less energy. These two observations led to the so-called neural hypothesis of intelligence efficiency, according to which it is not the intensity of the brain that is decisive, but the efficiency.

Too many cooks spoil the broth

Gench believes that his findings support this theory: “If you are dealing with a huge number of connections, where each can contribute to the solution of a problem, then it complicates the matter rather than helps him,” he says. According to him, it is the same as asking for advice even from those friends who do not understand TVs before buying a TV. Therefore, it makes sense to suppress interfering factors - this is the opinion of the neuroscientist from Bochum. Probably smart people do it better than others.

But how does this compare with the results of the Amsterdam group led by Natalia Goryunova? Erkhan Gench points out that the matter may be in different measurement techniques. Unlike the Dutch researcher, he did not examine individual cells under a microscope, but measured the movement of water molecules in tissues. He also points out that the degree of branching of pyramidal cells in different sectors of the brain may be different. "We are dealing with a mosaic that still lacks many pieces."

More similar research results are found elsewhere: the thickness of the gray matter layer is critical to intelligence - presumably because the bulky cortex contains more neurons, which means it has more "computational potential." To date, this connection is considered proven, and Natalia Goryunova once again confirmed it in her work. "Size matters" - this was established 180 years ago by the German anatomist Friedrich Tiedemann (Friedrich Tiedemann). “There is undeniably a link between brain size and intellectual energy,” he wrote in 1837. To measure the volume of the brain, he filled the skulls of deceased people with dry millet, but this connection is also confirmed by modern methods of measurement using brain scanners. According to various estimates, from 6 to 9% of the differences in IQ are associated with the difference in brain size. And yet the thickness of the cerebral cortex appears to be critical.

However, there is a lot of mystery here too. This applies equally to men and women, because in both sexes, smaller brains also correspond to smaller mental capacities. On the other hand, women have an average of 150 grams less brains than men, but they perform similarly to men on IQ tests.

“At the same time, the brain structures of men and women are different,” explains Lars Penke from the University of Göttingen. "Men have more gray matter, meaning their cerebral cortex is thicker, while women have more white matter." But it is also extremely important for our ability to solve problems. At the same time, at first glance, it does not play such a noticeable role as gray matter. The white matter is mainly composed of long nerve fibers. They can transmit electrical impulses over long distances, sometimes ten centimeters or more. This is possible because they are superbly isolated from their surroundings by a layer of fat-saturated substance - myelin. It is the myelin sheath and gives the fibers a white color. It prevents voltage loss due to short circuits and also speeds up the transfer of information.

Breaks in the "wires" in the brain

If pyramidal cells can be considered brain processors, then the white matter is like a computer bus: thanks to it, brain centers located at great distances from each other can communicate with each other and cooperate in solving problems. Despite this, white matter has long been underestimated by intelligence researchers.

The fact that this attitude has now changed is due, among other things, to Lars Penke. Several years ago, he found that white matter is in a worse state in people with reduced intelligence. In their brains, individual communication lines sometimes run chaotically, and not neatly and parallel to each other, the myelin sheath is not formed optimally, and from time to time even "wire breaks" occur. "If there are more such accidents, then this leads to a slowdown in information processing and ultimately to the fact that the individual on tests for intelligence shows worse results than others," explains the personality psychologist Penke. It is estimated that about 10% of the differences in IQ are due to the state of the white matter.

But back to the differences between the sexes: According to Penke, according to some studies, women are as successful at intellectual tasks as men, but they sometimes use other areas of the brain. The reasons can only be guessed at. In part, these deviations can be explained by the difference in the structure of the white matter - a communication channel between different centers of the brain. “Be that as it may, based on these data, we can clearly see that there is more than one and only opportunity to use the intellect,” emphasizes the researcher from Bochum. "Different combinations of factors can lead to the same level of intelligence."

Thus, a “smart head” is made up of many components, and their ratio can vary. Pyramidal cells are also important as efficient processors, and white matter as a system of fast communication and a well-functioning working memory. Added to this are optimal cerebral circulation, strong immunity, active energy metabolism, and so on. The more science learns about the phenomenon of intelligence, the clearer it becomes that it cannot be associated with only one component and even with one specific part of the brain.

But if everything works as it should, then the human brain is capable of doing amazing things. This can be seen in the example of South Korean nuclear physicist Kim Un Young, who, with an IQ of 210, is considered the smartest person on Earth. At the age of seven, he was solving complex integral equations on a Japanese television show. At the age of eight, he was invited to NASA in the United States, where he worked for ten years.

True, Kim himself warns against attaching too much importance to IQ. In a 2010 article in the Korea Herald, he wrote that highly intelligent people are not omnipotent. Like world records for athletes, high IQs are just one manifestation of human talent. "If there is a wide range of gifts, then mine is only part of them."