Neuronal pruning: what it is, features and associated diseases

As we know, our brain is made up of neural or synaptic networks that allow information to be processed continuously.

These networks are made up of millions of interconnected neurons. And at the same time, these connections have a significantly higher number during the first years of life than during our adulthood. As a result, our brain suffers from what is called neuronal pruning in order to reject synaptic connections that we are not using.

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

    What is neuronal pruning?

    At birth, we have more neural connections than the rest of our lives, and we can have 5 times as many synaptic connections as we need, even though a baby’s brain is larger. small and that it grows as the individual develops.

    Neuronal pruning, also known as synaptic pruning, consists of a process of clearing synaptic connections that the brain does not use during the developmental stage that takes place in childhood and, especially, adolescence. Thus, through this process, useful brain connections are refined, allowing the brain to function more efficiently and adapt better to the environment.

    The process by which neuronal or synaptic pruning takes place 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 increasing its size to about 5 times the size and neuronal pruning, as we will explain below.

      Several investigations on this subject have consisted in verifying that during the first years of life, people have a much higher number of synaptic and neural connections than in adulthood.

      This is why it is considered that this neuronal overproduction ensures that during these stages where learning is fundamental (for example, learning to walk, speak, write, etc.) the appropriate synaptic connections are established to consolidate these learnings, rejecting by way neuronal or synaptic. prune 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 takes place at a breakneck pace until the age of 2 about people, so a baby has a lot more neurons and synaptic connections than he needs.

      This overproduction of neurons and synaptic connections during the first years of life is believed to allow the brain to have the maximum capacity to adapt to the environment and, therefore, to form multiple synaptic connections to consolidate this that was learned. .

        Beginning of neuronal pruning

        Given the excess of neurons and synaptic connections, from the age of 3 begins the process of neuronal or synaptic pruning, in which unused neural connections start to be destroyed while useful ones are strengthened and myelinated so that you can process information more efficiently and quickly. Through this process of refining 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 adolescence, when large-scale neuronal pruning develops.

        Neuronal pruning in adolescence

        It is estimated that the greatest neuronal pruning occurs during adolescence, so that about half of synaptic or neural connections are lost in some areas of the brain, being quite inferior in others. On another side, there is a marked increase in infant myelin production, which facilitates this increase in the speed of information flow through synaptic connections.

        Research indicates that neuronal pruning helps, when people reach adolescence, to “rewire” synaptic connections in patterns similar to those they have as adults. In this way, the synaptic connections learn to function with greater synchronization, so that the efficiency of the brain is increased and the brain will also have to consume less energy to function properly.

        To put it simply, we will imagine that neuronal or synaptic connections constitute a roadmap or a gps. Well, when in our early years of life our synaptic connections are much higher than what we need in adulthood and that is why in our process of growing and learning these paths that we use often are strengthened, while those we do not use are destroyed. and so shortcuts are formed to transmit information through our neural circuit. In this way, our brain becomes more efficient.

        However, it should also be noted that not only neuronal pruning of those synaptic connections that are not being used occurs. Because brain plasticity has been shown to occur throughout life, and even more so in those early years when countless knowledge is gained, synaptogenesis or the formation of synaptic connections also occurs.

        For example, when we acquire new knowledge (for example, the name of the capitals of all the countries of a continent) or learn a new skill (for example, to play the piano) new synaptic connections are established to consolidate new learning in our brainas well as to strengthen the links which already exist by deepening the knowledge of a subject already known or by improving a competence already acquired.

          Adverse factors for proper neuronal pruning

          As we have seen, the neural pruning process allows humans to tailor synaptic connections to the demands of the environment, so that unused connections are discarded, as well as those that are used more are strengthened.

          However, neuronal pruning does not always occur effectively, as a number of factors hinder this process.

          Lack of stimulation

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

          In this sense, children who during these first years of life have low stimulation, will undergo neuronal pruning above normal. This poor stimulation also results in less development of the temporal cortex (responsible for emotions, language and memory).

            Trauma at an early age

            It was found that when a child suffers from some kind of trauma, the neuronal pruning of his brain is obstructed, so that its network of synaptic connections is excessively thick.

            When the synaptic networks are too thick, as if there was a synaptic deficit, the development of social behavior is severely affected and may influence the development of dissocial behavioral disorders.

            This hypothesis was corroborated by a study from King’s College London which found by brain scans that children who exhibited traits of cruelty had excessively thick neural connections in certain areas of the brain (anterior cingulate cortex and orbitofrontal cortex, with a important function in empathy and emotional control), unlike children who lacked these traits and had no brain areas with excess synapse.

            It should be noted that there are studies that have found a relationship between consumption alcohol and drugs during adolescence with poor 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.

              Relationship between neuronal pruning and schizophrenia

              A recent study at Harvard University, led by Steve McCarroll, found evidence that there may be a relationship between neuronal pruning and schizophrenia, such as when neuronal pruning does not occur properly in adolescence, it could promote the development of schizophrenia.

              The researchers in this study found that the C4 gene on chromosome six, in addition to being linked to the immune system, is also responsible for modulating neuronal pruning, finding that when there is a much higher number of synaptic connections than necessary or those remaining connections are wrong, the development of schizophrenia could occur.

              This gene 4 codes for the proteins 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 syntheses, so if there were too many of them, it could trigger drastic neuronal or synaptic pruning triggering schizophrenia.

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

              Bibliographical references

              • Lozano, A. and Ostrosky, F. (2011). Development of executive functions and the prefrontal cortex. Journal of Neuropsychology, Neuropsychiatry and Neuroscience, 11 (1), p. 159-170.
              • Markowitsch, HJ and Staniloui, A. (2014). Neurophysiology of (anti) social behavior. Mind and Brain, 69, p. 60-65.
              • Nelson, CA, Furtado, EA, Fox, NA & Zeanah, CH (2011). The sensitive years. Mind and Brain, 46, p. 9-17.
              • Sekar, A. et al. (2016). Risk of schizophrenia due to a complex variation of the component of complement 4. Nature, 530, p. 177-183.
              • Spear, LP (2012). Adolescent neurodevelopment. Journal of Adolescent Health, 52, pages S7-S13.
              • Rohlfs, P. (2016). Development of the human nervous system. General perspective of the prenatal stage until 2013. International Journal of Psychology, 1 (15), p. 1-50.
              • Triglia, A., Regader, B. and García-Allen, J. (2016). Psychologically speaking. Barcelona: Paidós.

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