Neuroplasticity: How does the brain adapt to adverse situations?

Tuesday, 04 de February de 2020

Until recently it was believed that the brain was a fixed and immutable organ, being unable to generate new connections and cells [3]. However, it is known through current research that the nervous system (NS) has the ability to change its morphology and physiology according to the internal and external stimuli that it undergoes on a daily basis. This process is called neuroplasticity or neuronal plasticity [1, 3, 4].

Neuroplasticity can be defined as the capacity that the SN has to adapt to the adversities of the environment in which it presents itself [1, 3]. Therefore, it promotes biological, biochemical, physiological and morphological changes in nerve cells, especially in neurons, in order to adapt to stimuli [1, 3]. It can present itself in several ways: regenerative, axonic, synaptic, somatic and dendritic. This phenomenon occurs in physiological and pathological conditions, allowing the formation of new neural networks and circuits.

According to Ramón y Cajal (1913), “in adults, the nervous paths are something fixed, finalized and immutable. Everything can die, nothing can be regenerated ”[1, 3]. Don Santiago Ramón y Cajal was one of the first researchers to study the possibility of NS being shaped by the environment. His descriptions yielded a book, whose theme “Estudios sobre la degeneración y regeneración del sistema nervioso”, published in 1913 in the city of Madrid, Spain, describes descriptions of uncertainties, questions and future expectations regarding the most important system of the human body. In this book, Cajal suggested that NS was fixed and immutable, however neuroplasticity was possible, but it would be demonstrated only in future generations.

It was only in 1909 that the term neuroplasticity was used for the first time by Minea [6] to attribute the capacity in which nerve cells have to adapt to the environment in which they find themselves. Until that moment there was nothing proven, but 60 years after Ramón y Cajal's postulates were published, and Jhon Eclans in 1973, was able to find convincing evidence about such descriptions.

Neuroplasticity is present in both cases, during pathological processes and injuries in the NS, as well as, it is part of the normal physiology of our body from ontogeny (embryology) to adulthood and death [5]. In most cases, we attribute neuroplasticity to the NS adaptation process in the event of trauma [1, 2, 4]. In lesions, neuroplasticity appears in an attempt to promote tissue repair or regeneration, with the purpose of reestablishing the normal functions of neurons, for example, we can mention lesions in the NS, such as spinal cord injury and sciatic nerve injury. In this case, we call it regenerative neuroplasticity, which can be axonic, dendritic or somatic [5].

However, it must be understood that neuroplasticity is an intrinsic physiological process of the human being, in which the brain adapts to external and internal conditions, being fundamental to the neurochemical process of learning and memory [5, 3], as they are they do by forming new brain connections.

Neuroplasticity has maximum activity during the critical period [5]. During this phase, NS is more plastic and more susceptible to changes in the external environment. The critical period occurs in the development of NS during the embryonic phase. After birth, brain plastic activity decreases considerably, but never ceases to exist. This implies that even the elderly have reduced neuronal plasticity. This factor also explains why children find it easier to learn than adults and the elderly. They have greater neuronal plasticity. Their synapses and connections are made more quickly and in case of injury in the NS tend to regenerate more easily.

The extracellular environment microenvironment also influences the nerve regeneration process [2]. Studies show that the microenvironment can contribute to morphological plasticity, which is characterized by changes in the dendritic tree, formation of new neural circuits due to changes in the path of nerve fibers, changes in the number of synapses and changes in dendritic spines [5].

The neuronal region in which it is affected also influences regenerative neuroplasticity. Extensions such as axons and dendrites are easier to be restored and recovered, however, if the injury is at the somatic level, that is, in the neuron cell body, regeneration becomes impossible leading to neuronal death [5].

Therefore, contrary to what scientists believed in the past, NS is not fixed and immutable. It has a capacity for regeneration, some regions are easier to regenerate than others, this occurs due to the presence or absence of stimulating and inhibiting factors. Additionally, neuroplasticity is also attributed to contact with stimuli. Reading habit, practicing physical activities, healthy eating, learning other languages, learning musical instruments, are factors that stimulate synaptogenesis and neurogenesis (neuroplasticity in general) allowing this individual to have a faster learning ability and ability [1,2 , 5.6]. However, if a person is not in the habit of reading or getting to know new skills and activities, their nervous connections tend to atrophy, thus causing greater difficulty in learning.

It is worth mentioning that permanent structural and physiological changes generated from constant exposure to external stimuli can promote behavioral and psychological changes. Therefore, constant exposure of individuals to stress and chronic anxiety conditions, can generate behavioral changes [1] that lead to depressive conditions. Therefore, we call behavioral plasticity [5].

References:

Eberhard Fuchs, E.; Flügge, G. Adult Neuroplasticity: More Than 40 Years of Research. Neural Plasticity, 2014.

Knvul Sheikh. How the Brain Can Rewire Itself After Half of It Is Removed. 2019

https://www.nytimes.com/2019/11/19/health/brain-removal-hemispherectomies-scans.html

Kania, B. F.; Wrońska, D.; Zięba, D. Introduction to Neural Plasticity Mechanism. Journal of Behavioral and Brain Science, 2017

https://www.scirp.org/pdf/JBBS_2017020615374293.pdf

Sobrinho, J. B. R. Neuroplasticidade e a Recuperação da Função após lesões Cerebrais. Acta Fisiátrica 2(3): 27-30, 1995.

Lent, R. 100 bilhões de neurônios. Conceitos Fundamentais de Neurociências. Atheneu, 2001.

Yochim, R.; Woodhead, E. Psychology of Aging: A Biopsychosocial Perspective. Springer Publishing Company, 2017.

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Autor:

Tamara Nunes

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