Neuronal pruning: what is it, characteristics and associated diseases?

These are the stages and characteristics of neuronal pruning, key to understanding the brain.

As is well known, our brain is composed of neuronal or synaptic networks that make it possible to constantly process information.

These networks are composed 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 adulthood. Therefore, our brain undergoes what is known as neuronal pruning in order to discard those synaptic connections that we do not use.

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

What is neuronal pruning?

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

Neuronal pruning, also known as synaptic pruning, consists of a process of eliminating synaptic process of eliminating synaptic connections that the brain does not use during the developmental stage that takes place in infancy and, above all, in adolescence.. Thus, thanks to this process, the brain connections that are useful are refined, making the brain's functioning more efficient and better adapted to the environment.

The process of neuronal or synaptic pruning during childhood and adolescence will be briefly discussed below.

Stages of this process in the nervous system.

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

Several researches on this subject have been able to prove that during the first years of life people have a much higher number of synaptic and neuronal connections than in adulthood..

This is why it is considered that this neuronal overproduction ensures that during these stages where learning is fundamental (e.g., learning to walk, speak, write, etc.) the appropriate synaptic connections are established to consolidate such learning, discarding through neuronal 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, known as synaptogenesis. This process occurs at a frenetic pace until about 2 years of age, so that new neurons and synaptic connections between them begin to form. This process occurs at a frenetic rate until about 2 years of age, so that a baby has far more neurons and synaptic connections than it will ever need.

This overproduction of neurons and synaptic connections during the first years of life is considered to allow the brain to have the maximum possible capacity to adapt to the environment and, consequently, to form multiple synaptic connections to consolidate what it has learned.

Beginning of neuronal pruning.

Given the excess of neurons and synaptic connections, the process of neuronal or synaptic pruning begins at the age of 3 years.In this process, the neuronal connections that are not used begin to be destroyed while those that are useful are strengthened and myelinated so that you can process information more efficiently and at a higher speed. Thanks to this process of refinement of the synaptic connections, these acquire a higher degree of specialization.

Nevertheless, during childhood synaptogenesis continues to increase, although to a lesser extent than during the first two years of life, until adolescence, when large-scale neuronal pruning develops.

Neuronal pruning in adolescence

It is estimated that during adolescence is when the greatest neuronal pruning occurs, so that about half of the synaptic or neuronal connections are lost in some regions of the brain, being considerably less in others. On the other hand, there is a notable increase in myelin production with respect to infancy, which facilitates this increase in the speed of information flow through synaptic connections.which facilitates this increase in the speed of information flow through synaptic connections.

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

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

However, it should also be noted that not only a neuronal pruning of those synaptic connections that are not used is produced.. 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 synaptogenesis or the formation of synaptic connections.

For example, when we acquire new knowledge (e.g., names of the capitals of all the countries of a continent) or are learning a new skill (e.g., playing the piano) new synaptic connections are produced in order to consolidate the new learning in our brain, as well as to reinforce the existing ones.The connections that we already have are also reinforced when we deepen our knowledge of an already known subject or when we improve a previously acquired skill.

Factors detrimental to proper neuronal pruning.

As we have been able to verify, the process of neuronal pruning allows human beings to adapt their synaptic connections to the demands of the environment, so that the connections that are not used are discarded, while those that are most used are reinforced.

However, neuronal pruning does not always occur efficiently, since there are a number of factors that impair this process.

Lack of stimulation

The process of neuronal pruning is strongly influenced by the environment, so that it is during the first years of life it is essential that infants and children receive sufficient stimulation from adults in order to acquire new learning skills. to acquire new learning, as well as to consolidate what they have already acquired.

In this sense, children who are poorly stimulated during these first years of life will suffer a greater than normal neuronal pruning. This poor stimulation also has repercussions on a lower development of the temporal cortex (in charge of emotions, language and memory).

Trauma at early ages

It has been found that when a child suffers a trauma of any kind, the neuronal pruning of his brain is hindered, so that his synaptic network is excessively crowded.The synaptic network of connections is excessively dense.

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

This hypothesis was corroborated by a study at King's College London, which found through brain scans that children who showed cruelty traits had exaggeratedly dense neuronal connections in some areas of the brain (the anterior cingulate cortex and the orbitofrontal cortex, with an important function in empathy and emotional control), unlike children who did not show such traits and did not have any brain area with excess synapses.

It should be noted that studies have found a link between alcohol and drug use during adolescence and impaired neuronal pruning.. A close relationship has also been found between defective neuronal pruning and the development of schizophrenia, as will be explained in more detail below.

• Related article, "What is trauma and how does it influence our lives?"

Relationship between neural pruning and schizophrenia.

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

The researchers in this study found that the C4 gene on chromosome six, in addition to being related to the immune system, is also responsible for modulating neuronal pruning, finding that when there are far more synaptic connections than necessary or these excess connections are erroneous, the development of schizophrenia could arise.

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

It should be noted that this finding could demonstrate one of the causes of this disease, given that schizophrenia does not originate from a single cause.It is known that the influence of the environment in which the person grows up is also very important, among other factors.