Effect of Early Life Stress on Behavior and Cognition
The human brain undergoes rapid development from late gestation to early childhood. The brain structures that are developing or undergoing age-related changes are more vulnerable to the effects of stress. Trauma at different time points in an individual’s life might be associated with different outcomes, depending on the brain structure that was affected at the time of exposure to adversity.
The hippocampus, the amygdala and the frontal lobes of the brain are responsible for development of cognitive and emotional functions. Repeated exposure to stress triggers the activation of the hypothalamus-pituitary-adrenal (HPA) axis, resulting in production of glucocorticoids by the adrenal gland. Glucocorticoids are essential for normal brain maturation and its receptors are expressed throughout the brain. Skewed levels of glucocorticoid impair maturation and survival of different brain cells. Hence, expression of glucocorticoids can have long lasting effects on the regions of the brain that regulate their release.
Exposure to stress when these regions of the brain undergo changes may result in long time cognitive and behavioral defects. The effects of stress at different periods of life interact and may manifest after an incubation period.
Maternal depression, intrauterine under-growth and low birth weight are indices of prenatal stress. Low socio-economic status, maltreatment, sexual abuse and war are considered adverse events causing postnatal stress.
Negative effects of stress in the prenatal period may manifest during childhood in the form of behavioral, neurological and cognitive disturbances. These developmental disorders include unsocial and inconsiderate behavior, attention deficit hyperactivity disorder (ADHD), sleep disturbances as well as psychiatric disorders like depressive symptoms, excessive amygdala functioning (fear reaction) and mood and anxiety disorders. However, quality postnatal care often moderates these negative effects.
The hippocampus continues to develop till the age of two years, and so it is extremely vulnerable to the effects of chronic stress. It has been clearly demonstrated that in children who were physically healthy at birth, severe abuse in the early years of life is associated with reduced brain volume. This reduction in volume decreases with increasing age of onset and increases with increased duration of the maltreatment. Children suffering from long hours of neglect are at higher risk of behavioral problems such as novelty-seeking, addictive behaviors and chronic depression later in life.
The frontal cortex undergoes major development during adolescence. Adolescents exposed to early postnatal stress are at a higher risk of developing depression. Also stress during adolescence may result in various psychopathologies such as anxiety and depression.
In adulthood and old age the brain regions that undergo the most rapid decline as a result of aging are highly vulnerable to the effects of stress hormones. Higher stress results in increased glucocorticoid levels. This in turn affects the frontal lobe and hippocampal volume negatively resulting in cognitive impairments.
This research reiterates the importance of rehabilitation of children affected by war, strife and abuse. Better monitoring of state care or orphanages is also needed. Moreover, we require stricter social policies aimed at protecting the most vulnerable section of the society — the children — in the family home from the long term deleterious effects of stress on brain, behavior and cognition.
Lupien, S., McEwen, B., Gunnar, M., & Heim, C. (2009). Effects of stress throughout the lifespan on the brain, behaviour and cognition Nature Reviews Neuroscience, 10 (6), 434-445 DOI: 10.1038/nrn2639
McGowan, P., Sasaki, A., D’Alessio, A., Dymov, S., Labonté, B., Szyf, M., Turecki, G., & Meaney, M. (2009). Epigenetic regulation of the glucocorticoid receptor in human brain associates with childhood abuse Nature Neuroscience, 12 (3), 342-348 DOI: 10.1038/nn.2270
Charmandari, E., Kino, T., Souvatzoglou, E., & Chrousos, G. (2003). Pediatric Stress: Hormonal Mediators and Human Development Hormone Research, 59 (4), 161-179 DOI: 10.1159/000069325