Neural pruning: what is it, characteristics and associated diseases

As is known, our brain is made up of neural or synaptic networks that make it possible to constantly process information.

These networks are made up of millions of neurons that are interconnected. And in turn, these connections have a significantly higher number during the first years of life than during our adult stage. Therefore, our brain undergoes what is known as neuronal pruning in order to discard those synaptic connections that we do not use.

Thanks to neural pruning our brain becomes more efficient and responds better to the demands of the environment.

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What is neural pruning?

When we are born we have a greater number of neural connections than the rest of our lives, being able to have a 5 times greater number of connections synaptic than are necessary, despite the fact that a baby's brain size is smaller and grows as the baby develops. individual.

Neural pruning, also known as synaptic pruning, consists of a process of elimination of synaptic connections that the brain does not use during the stage of development that takes place in childhood and, especially, in adolescence

. So, thanks to this process, useful brain connections are refined, making it easier for the brain to function more efficiently and better adapt to the environment.

Next, the process through which neural or synaptic pruning passes during childhood and adolescence will be briefly commented.

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Stages of this process in the nervous system

The development of the human brain during childhood and adolescence undergoes various changes, such as the increase of its size up to approximately 5 times its size and neural pruning, as we will explain to continuation.

Various investigations in this regard have been to verify that during the first years of life people have a much higher number of synaptic and neural connections than in adulthood.

That is why it is considered that this neuronal overproduction ensures that during these stages where learning is essential (p. g., learning to walk, speak, write, etc.) adequate synaptic connections are established to consolidate these learning, discarding through neural or synaptic pruning those synaptic connections that have not been used.

Synaptogenesis or synaptic formation

From the embryonic stage, new neurons and synaptic connections between them begin to form, which is known as synaptogenesis. This process occurs at a frenetic pace until 2 years of age of people approximately, so that a baby has a number of neurons and synaptic connections much higher than she will need.

It is considered that this overproduction of neurons and synaptic connections during the first years of life allows the brain to have the maximum possible capacity to adapt to the environment and, consequently, form multiple synaptic connections to consolidate what has been learned.

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Beginning of neural pruning

Given the excess of neurons and synaptic connections, from the age of 3, the neural or synaptic pruning process begins, in which the neural connections that are not used begin to be destroyed at the same time that those that are useful are seen strengthened and myelinated so that you can process information more efficiently and at a faster speed. higher. Thanks to this process of refining the synaptic connections, they acquire a higher degree of specialization.

However, during childhood synaptogenesis continues to increase, although to a lesser extent than during childhood. first two years of life, until reaching adolescence, which is when neuronal pruning develops to a great extent. scale.

Neural pruning in adolescence

It is estimated that during adolescence is when the greatest neuronal pruning occurs, so that it is lost close to half of the synaptic or neural connections in some brain regions, being considerably less in other Secondly, there is a marked increase with respect to childhood in myelin production, which facilitates this increase in the speed of the flow of information through synaptic connections.

There is research that claims that neural pruning helps when people reach adolescence there is a "rewiring" of synaptic connections in patterns similar to those they have in the stage adult. In this way, synaptic connections learn to function with greater synchronization, so the brain efficiency is increased and also the brain will need to consume less energy to function correctly.

To put it simply, let's imagine that the neural or synaptic connections constitute a road map or GPS. Well, when in our first years of life our synaptic connections are highly superior to those that we will need during our adult stage and that is why during our growth and learning process those routes that we use with frequency, while those that we do not use are destroyed and thus shortcuts are formed to transmit information through our circuit neuronal. In this way our brain becomes more efficient.

However, it should also be noted that not only does a neural pruning of those synaptic connections that are not used. Since brain plasticity has been shown to occur throughout life and, even more so, during these early years, where innumerable knowledge is acquired, there is also a synaptogenesis or formation of connections synaptic.

For example, when we acquire new knowledge (p. g., name of the capitals of all the countries of a continent) or we are learning a new skill (p. e.g., playing the piano) new synaptic connections are produced in order to consolidate the new learning in our brainAs well as reinforcing the connections that already exist when deepening the knowledge of an already known topic or improving a previously acquired skill.

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Detrimental factors for proper neural pruning

As we have seen, the neural pruning process allows human beings to adapt their synaptic connections to the demands of the environment, so that the connections that are not used are discarded, as well as those that are most they use.

However, neural pruning does not always take place efficiently, since there are a number of factors that impair this process.

Lack of stimulation

The neural pruning process has a strong influence from the environment, so that during the first years of life it is essential that babies and children receive sufficient stimulation from adults in order to acquire new learning, as well as to consolidate those already acquired.

In this sense, children who during these first years of life have a poor stimulation, will suffer a neuronal pruning greater than normal. This poor stimulation also affects a lower development of the temporal cortex (responsible for emotions, language and memory).

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Traumas at an early age

It has been found that when a child suffers some kind of trauma, the neural pruning of his brain is hampered, so that its network of synaptic connections is excessively dense.

When synaptic networks are excessively dense, as if there is a deficit of synapses, the development of social behavior is severely affected, and may influence the development of conduct disorders.

This hypothesis was corroborated by a study from King College London that found through brain scans that children who displayed traits of cruelty had exaggeratedly dense neural connections in some areas of the brain (the anterior cingulate cortex and the orbitofrontal cortex, with a function important in empathy and emotional control), unlike the children who did not present these traits nor did they possess a brain area with excess synapse.

Notably there are studies that have found a relationship between alcohol and drug use during adolescence with poor neural pruning. A close relationship has also been found between faulty neural pruning and the development of schizophrenia, as will be explained in more detail below.

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Relationship between neural pruning and schizophrenia

A recent study at Harvard University, led by Steve McCarroll, found indications that there might be a relationship between neural pruning and schizophrenia, as when neural pruning does not occur correctly in adolescence, this could favor the development of schizophrenia.

The researchers of this study found that the C4 gene on chromosome six, apart from being related to the immune system, is also responsible for modulating pruning neuronal, finding that when there is a number of synaptic connections much higher than necessary or these excess connections are wrong, the development of the schizophrenia.

Said gene 4 encodes the proteins that are responsible for marking the synaptic connections that must be pruned. In the study, they found a variant of the C4 gene that increased the number of protein syntheses, so that if there were too many this could trigger drastic neural or synaptic pruning triggering schizophrenia.

It should be noted that this finding could demonstrate one of the causes of this disease, since schizophrenia is not caused by just one cause, since it is known that the influence of the environment in which the person grows is also very important, among other factors.