[Neurobiological inscriptions of psychological trauma during early childhood].

Neurodevelopment is a highly complex process, influenced by a wide range of interacting genetic and environmental factors. Recent developments in fetal, neonatal and infant behavioural genetics and brain imaging methods have allowed for more detailed investigation of the effects of early adverse environment on the developing brain. This review aims to provide background for neurobiological understanding of how the prolonged exposure to stress or trauma during early childhood affects subsequent cognitive, emotional and social development. Initially, a brief overview of brain development is provided - focusing, in particular, on the limbic system structures, which are closely linked to emotional experiences and reactions, learning and memory. Emphasis is placed on the concept of neural plasticity, which is the biological base of memory and learning - the two most important mechanisms through which the environment affects the behavior. Moreover, the concept of sensitive periods, that is to say periods of "vulnerability" or "opportunity" during which particular experiences affect brain growth, functional organization and maturation, is discussed. Brief overview of the neuroendocrine stress response system and the long-term effects of prolonged exposure to stress hormones on early brain development clarify further why children are more vulnerable than adults to the effects of stress. The section dealing with the memory, which is closely linked to the limbic system, attempts to discuss how early exposure to chronic stress or psychological trauma, through neurobiological effects and the process of learning, can lead to dysfunctional behaviors, which in its extreme form can be mental disorders. The two types of memory are discussed: (a) the implicit (nondeclarative), which develops during the prelingual stage of child's development and refers to unconscious memories of previous experiences, and (b) the explicit (declarative) memory, which is closely linked to language development and refers to memories that can be consciously recalled. Given that prenatal or postnatal early experiences can alter the course of brain development, the exposure to maltreatment, whether it takes the form of physical, sexual or emotional abuse, or the kind of extreme neglect and deprivation during the early years of life, is related to alterations in brain structure and function, which in turn contributes to development of chronic post-traumatic disorder (PTSD), anxiety, mood and attachment disorders, memory and learning problems, and other psychopathological conditions. Finally, it is pointed out that a comprehensive and detailed diagnostic assessment of young children who are referred to the child and adolescent mental health services because of presenting with behavioural and emotional disturbances should be an established good clinical practice, given that a wrong diagnosis may have further deleterious effects on the child's psychosocial development. The need for neuropsychological assessment of children who have been exposed to early trauma or stress is thought to have important implications for the recognition and the neurobiological understanding of early trauma, which in turn allows for the development and implementation of appropriate interventions.