How does stress shape our brain? Childhood is the critical period

Who has not experienced stress in their life, whether associated with work, studies or financial or family problems. Our body's response to stress is good: adaptive and totally necessary for our survival as a species. It keeps us on alert to be able to face everyday challenges.

But what happens when this state of alert is maintained for a long time? This is what we call chronic stress and it can have a very negative effect on our mental health.

In this context, it is worth asking: are we equally vulnerable to chronic stress at all stages of our lives? Does a trauma suffered in childhood have the same consequences as one suffered in adulthood or in senescence? The answer is no, and the key is in the plasticity of our brain.

The first two years of life, keys
During early childhood, the neural networks that intervene in the development of our emotions are configured. In this period, plasticity is very high. Specifically, the first two years of life are essential for adequate brain development and the acquisition of socio-affective skills.

In this phase, which we call the “critical period of plasticity,” the environment is very effective in producing long-term changes in our brain and, consequently, in our behavior. The closure of this period is crucial for the maturation and stabilization of neural circuits; once finished, the plasticity is very limited. We could use chewing gum as a simile: when you start chewing it, it is very moldable, but over time it becomes harder and more difficult to shape (limited plasticity, but not non-existent).

An enriching environment in childhood produces plastic changes in the brain that promote resilience; that is, the ability to overcome traumatic circumstances. On the contrary, childhood trauma, such as suffering abuse, is a risk factor for the development of a multitude of neuropsychiatric disorders and pathological behaviors, such as schizophrenia, anxiety-depressive disorders, violence or addiction. In fact, 45% of disorders that appear during childhood and 30% of those that emerge in adulthood are directly related to child abuse.

According to the World Health Organization, neglect – defined as the failure to meet a child's physical, medical, educational or emotional needs – is the most common type of abuse. Recent studies have shown that depending on the type of neglect suffered and depending on gender, the effects on the brain and behavior are different. Hence the importance of gender inclusion in research.

A delicate balance of connections
Synapses (the mechanism that neurons use to communicate) vary with age. These synapses are very fast and efficient; If there is a failure, the connection is not established well and neuronal alterations appear.

Broadly speaking, we can classify synapses as excitatory or inhibitory. The excitatory ones are generated mainly in the perinatal stage and early childhood, reducing during adolescence (the so-called synaptic pruning), while the inhibitory ones have an inverse time course. For this reason, a two-year-old boy or girl is not aware of the risk of crossing the road without looking for cars.

This is where the prefrontal cortex comes into play, a region located in the most anterior part of the brain and very important in decision making. At two years of age, this area has not yet matured and, therefore, there is no balanced balance between both types of synapses.

Could stress affect this imbalance and trigger the appearance of socio-affective alterations? Many studies demonstrate that imbalances in the excitation/inhibition balance are, indeed, relevant to explaining the appearance of numerous psychiatric diseases.

Now, knowing the cellular and molecular consequences of stress in the human brain is complicated. Therefore, the use of animal models is vital in this field of study.

Loneliness, the biggest cause of stress at older ages
If we look for scientific articles on the effects of stress in people over 60 years of age or in animal models of aging, we will see that there is little published.

Even so, social isolation is known to affect one in three older adults in Europe. It is the most common stressor at this stage of life and the one most related to depressive disorders, especially in women.

Social relationships are necessary to survive, but as we age we spend more time alone. Without going any further, after the covid-19 pandemic, the number of cases of depression increased in the elderly population. And as we know, many of these people were home alone during the pandemic.

Returning to the chewing gum simile, our brain becomes less moldable over time, although brain plasticity never ceases to exist. Therefore, during our childhood and adolescence we are more vulnerable to stress, which does not mean that it cannot affect our brain (a lot) during adulthood and old age. The appearance of psychiatric diseases or socio-affective alterations will depend on the moment in our life in which we suffer stress and the type of stressor that triggers it.

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Source: The Conversation. Authorship:

Aroa Mañas Ojeda
Student of the Biomedical Sciences and Health Doctoral Program at the NEST Research Group, Universitat Jaume I

Esther Castillo-Gómez
Professor of Human Anatomy and Embryology. Doctor in Neurosciences. Principal researcher of the NEST group. G23 CIBERSAM researcher. Department of Medicine, Universitat Jaume I