Neuronal Pruning: What It Is, Characteristics And Associated Diseases
As is known, our brain is made up of neuronal 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 adulthood. For this reason, 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.
When we are born we have a greater number of neuronal connections than the rest of our lives, and we can have 5 times the number of synaptic connections than are necessary, despite the fact that the size of a baby’s brain is smaller and grows as it grows. the individual is developing.
Neuronal pruning, also known as synaptic pruning, consists of a process of eliminating synaptic connections that the brain does not use during the stage of development that occurs in childhood and, above all, in adolescence So, thanks to this process, the brain connections that are useful are refined, which makes it easier for the brain to function more efficiently and better adapt to the environment.
The process by which neuronal or synaptic pruning occurs 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 various changes, such as an increase in its size to approximately 5 times its size and neuronal pruning, as we will explain below.
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 neuronal connections than in adulthood
That is why it is considered that this neuronal overproduction makes it possible to ensure that during these stages where learning is essential (e.g., learning to walk, speak, write, etc.) the appropriate synaptic connections are established to consolidate said learning, discarding through neuronal or synaptic pruning those synaptic connections that have not been used.
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 much higher number of neurons and synaptic connections than it 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.
Beginning of neural pruning
Given the excess of neurons and synaptic connections, From the age of 3, the process of neuronal or synaptic pruning begins, in which the neural 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 synaptic connections, they acquire a greater degree of specialization.
However, during childhood synaptogenesis continues to increase, although to a lesser extent than during the first two years of life, until reaching adolescence, which is when large-scale neuronal pruning develops.
Neural 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 much lower in others. On the other hand, There is a notable increase in myelin production compared to childhood which facilitates this increase in the speed of information flow through synaptic connections.
There is research that states that neuronal pruning helps ensure that when people reach adolescence, a “rewiring” of synaptic connections occurs in patterns similar to those they have in adulthood. In this way, synaptic connections learn to function with greater synchronization, so brain efficiency is increased and the brain will also need to consume less energy to function correctly.
To put it simply, let’s imagine that neuronal or synaptic connections constitute a road map or GPS. Well, when in our first years of life our synaptic connections are greatly 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 frequently are strengthened, while Those that we do not use are destroyed and thus shortcuts are formed to transmit information through our neural circuit. In this way our brain becomes more efficient.
However, it is also worth noting that Not only does neuronal pruning occur in those synaptic connections that are not used Since brain plasticity has been shown to occur throughout life and, even more so, during these first years, where innumerable knowledge is acquired, synaptogenesis or the formation of synaptic connections also occurs.
For example, when we acquire new knowledge (e.g., name the capitals of all the countries on a continent) or are learning a new skill (e.g., play the piano) New synaptic connections are produced in order to consolidate new learning in our brain as well as the connections that you already have are reinforced when you deepen your knowledge of an already known topic or improve a previously acquired skill.
Detrimental factors for correct neuronal pruning
As we have seen, 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, as well as those that are used the most are reinforced.
However, neuronal pruning does not always occur efficiently, given that there are a series of factors that harm this process.
Lack of stimulation
The neuronal pruning process has a strong influence of the environment, so 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 what has already been acquired.
In this sense, children who have poor stimulation during these first years of life will suffer greater than normal neuronal pruning. This poor stimulation also results in less development of the temporal cortex (in charge of emotions, language and memory).
Trauma at an early age
It has been found that When a child suffers any trauma of any kind, the neuronal pruning of his or her brain is hindered so that its network of synaptic connections is excessively dense.
When the synaptic networks are excessively dense, as if there is a deficit of synapses, The development of social behavior is seriously affected, and may influence the development of dissocial behavior disorders
This hypothesis was corroborated by a study from King College London that found through brain scans that children who showed cruelty traits had exaggeratedly dense neural 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 present these traits nor did they have any brain area with excess synapses.
Notably There are studies that have found a relationship between alcohol and drug consumption during adolescence with deficient neuronal pruning A close relationship between defective neuronal pruning and the development of schizophrenia has also been found, as will be explained in more detail below.
Related article: “What is trauma and how does it influence our lives?”
Relationship between neuronal pruning and schizophrenia
A recent study at Harvard University, led by Steve McCarroll, found indications that there could be a relationship between neuronal pruning and schizophrenia, since When neuronal 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 neuronal pruning, finding that when there is a number of synaptic connections much higher than necessary or these excess connections are wrong, the development of schizophrenia could arise.
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 synthesis, so that if there were too many this could trigger drastic neuronal 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 a single cause since it is known that the influence of the environment in which the person grows is also very important, among other factors.
