The effects of early adversity on brain development

Early adversity related to child maltreatment influences the child's brain development. Researchers have studied these effects and their consequences.

Childhood and adolescence are crucial periods for brain development. It is during this period that the maturation of neuronal networks occurs, which allows the individual to develop cognitive  functions, emotional responses, representation of the world, and social behaviors. "This period of maturation is marked by great brain plasticity, a period during which the structural and functional organization of neuronal circuits is particularly influenced by experiences and the environment." explains Arnaud Tanti, associate researcher in integrative neurosciences at the Institut National de la Santé et de la Recherche Médicale (INSERM, French National Institute for Health and Medical Research).

Physical, psychological or sexual abuse or neglect during this period of life can therefore have significant effects on brain development. These effects can promote the emergence of psychological or psychiatric disorders such as depression. Thus, victims of child abuse are more likely to attempt suicide. Studies have been conducted on postmortem brain samples of people who committed suicide and who were victims of child abuse. Mr Tanti had the opportunity to work on these brain tissues from such subjects which have allowed to better understand the changes that can occur in the brain of a child exposed to early stress.

What is early stress ?

According to the World Health Organization (WHO), "stress is a state of mental worry or tension caused by a difficult situation. It is a natural human response to meet the challenges and threats we face in our lives". Stress has both physiological (on the body) and psychological (on the mind) effects. While mild stress is normal in daily life, and allows us to better deal with certain situations, a prolonged state of stress or an intense stress can be harmful physically and mentally. Harmful stress can generate anxiety and irritability ; disrupt sleep, eating, concentration and the ability to relax ; or cause body pains such as migraines or stomach aches.

The National Scientific Council on Child Development (Harvard University, USA) distinguishes three types of psychological stress : positive stress, a "natural" stress that allows the child to learn ; tolerable stress, which is more intense but can be overcome with the help of parents or guardians ; and toxic stress, a stress that lasts a long time and is abnormal. It is this last type of stress that can be generated in cases of physical, psychological, sexual abuse or neglect occuring during childhood, and which can be described as early stress/early adversity.

The effects of early stress on brain development

Studies of the brains of people who have been abused during childhood have identified several alterations in several areas of the brain. First, there is an increase in the volume and activity of the amygdala, suggesting an increased reactivity to stress. Second, there are changes in cortical and white matter activity, particularly in the prefrontal cortex, which plays a role in emotional control and cognition. In addition, stress leads to the production of cortisol, a hormone that helps manage stress. This hormone will alter the functioning of the brain to allow the individual to react to the stressful situation he/she is facing. In case of excessive production of cortisol in the brain, the individual's memory capacity, immune responses and response to stress, emotion and memory are impacted. Early stress, by its recurrence and/or its prolongation, will therefore result in an excessive production of cortisol, which will negatively impact the functioning of brain cells and harm the maturation process. There are also changes in brain structure and gene expression that affect sensitivity and response to stress, mood regulation, neurotransmission, neuronal plasticity, and neuroinflammation. Finally, early stress affects the myelination process. This process, which allows nerve fibers to be covered with a myelin sheath to facilitate the transmission of nerve signals, plays a very important role in communication between different regions of the brain.

To explain such effects on brain development, Mr Tanti points to the adaptive capacity of the human brain : "If child maltreatment, and stress in general, during this period of development has such persistent effects on victims, it is probably because first of all this adaptive capacity of the brain will perhaps direct the learning of behavior patterns that are more adapted to these toxic or aversive environments.". This adaptation of the brain during childhood therefore responds to adversity, to cope with it for a time, until the individual's limits are reached. However, this is detrimental to the individual who may suffer from a lack of adaptability and flexibility when faced with situations without adversity. In the most extreme cases, the individual may have integrated certain socially problematic behaviors (flight and withdrawal or aggression). The effects of early stress on brain development can therefore be irreversible and have a lifelong impact on the child.

Impacts on the victims and how to help them

Numerous studies have shown that exposure to abuse or neglect increases the likelihood of developing psychiatric disorders such as anxiety or depression. It also triggers and even worsens psychiatric illnesses such as bipolarity or schizophrenia. The changes that take place in the development of the brain of an individual confronted with early stress could thus play a role in the appearance of psychopathologies. For example, alterations in myelin in the cingulate cortex may contribute to behavioral dysregulation and the emergence of interpersonal difficulties, which contribute to the risk of depression and suicide. However, this hypothesis still needs to be substantiated as similar alterations are also present in individuals who have developed resilience.

There are many consequences of early stress, many inter-individual variations and many types of treatment. Furthermore, it is important to try to treat the harmful effects of early stress as soon as possible, ideally during childhood and at the latest during adolescence, so that we can still take advantage of the child's brain plasticity to treat him/her. To restore plasticity and learning capacity, recent studies also suggest the possibility of acting on the extracellular matrix - an assembly of macromolecules that allows cells to adhere and organize themselves into tissue - which plays an important role in brain plasticity and the maturation of neuronal circuits. This matrix could indeed be influenced by early stress, which would prematurely impair brain plasticity during childhood. "This could be an interesting lever, by acting on this extracellular matrix, to try to reopen windows of plasticity and facilitate adapted cognitive and emotional relearning, or perhaps promote resilience." explains Arnaud Tanti.

Gauthier Pichevin