Growing up in poverty or experiencing any adversity, such as abuse or neglect, during early childhood can put a person at risk for poor health, including mental disorders, later in life. Although the underlying mechanisms are poorly understood, some studies have shown that adverse early childhood experience leaves persisting (and possibly irreversible) traces in brain structure.
As neuroscientists who are investigating sensitive periods of human brain development, we agree: safe and nurturing environments are a prerequisite for healthy brain development and lifelong well-being. Thus, preventing early childhood adversity undoubtedly leads to healthier lives.
Poverty and adversity can cause changes in brain development. Harms can come from exposure to violence or toxins or a lack of nutrition, caregiving, perceptual and cognitive stimulation or language interaction. Neuroscientists have demonstrated that these factors crucially influence human brain development.
We don’t know whether these changes are reversed by more favorable circumstances later in life, however. Investigating this question in humans is extremely difficult. For one, multiple biological and psychological factors through which poverty and adversity affect brain development are hard to disentangle. That’s because they often occur together: a neglected child often experiences a lack of caregiving simultaneously with malnutrition and exposure to physical violence. Secondly, a clear beginning and end of an adverse experience is hard to define. Finally, it is almost impossible to fully reverse harsh environments in natural settings because most of the time it is impossible to move children out of their families or communities.
In a recently published study in Cerebral Cortex, we and our colleagues investigated the reversibility of altered brain structure in individuals who had recovered their sight after suffering from congenital blindness. Visual deprivation can be considered an extreme form of aberrant early childhood experience, and congenital blindness is known to cause a reduction in brain surface area similar to other types of aberrant childhood experience.
In this German-Indian collaboration, we used noninvasive magnetic resonance imaging (MRI) to examine the structure of the cerebral cortex, the folded outer layer of the brain that hosts billions of nerve cells and oversees perception, action and higher-level thinking. Our study investigated 21 children and adults—aged six to 36 at the time of the study—who had been born blind because of dense bilateral cataracts and who had gained sight through cataract removal surgery only months or even years later. Cataracts are the most common treatable cause of blindness worldwide. In Western countries, neonates born with cataracts typically receive surgery shortly after birth. In many resource-poor countries, however, cases regularly remain untreated for several years. Individuals with reversed cataracts constitute a unique human model for assessing the reversibility of impaired brain structure after aberrant childhood experience because the reason for their blindness can be fully eliminated at a clearly defined time point in life. Previous research has suggested that despite sight restoration surgery, individuals treated late for congenital blindness typically do not recover full visual capabilities but remain visually impaired throughout life.
In our recent study, individuals with reversed congenital cataracts were identified by the LV Prasad Eye Institute in Hyderabad, India. On average, they had been blind for seven years and had undergone cataract removal surgery 11 years prior to the study. We compared this group with three others: individuals with permanent congenital blindness; sight-recovery individuals who had vision at birth and only later developed cataracts; and sighted controls. From the brain scans, we created a three-dimensional model of each participant’s brain and used it to measure the surface area and thickness of the visual cerebral cortex.
We looked at the visual parts of the cerebral cortex to understand how early experiences shape the brain during development. In typical brain development, the cortical surface area expands until puberty, whereas cortical thickness increases during the first two years of life and decreases thereafter. This initial increase in cortical thickness is considered to reflect an explosion of synapses, that is, connections between neurons, while the subsequent thinning is thought to reflect a pruning away of unused connections. Structural changes are essential for the refinement and maturation of neural circuits.
In our study, we observed that individuals with reversed congenital cataracts had a smaller visual cortical surface area and a higher thickness than what is found in sighted individuals of their respective age. Despite many years of having their vision restored, these sight-recovery individuals had a visual cortex that more closely resembled the corresponding visual areas of individuals with permanent blindness. Similar changes were not detected in individuals with reversed cataracts that emerged later in childhood. Importantly, the degree of structural impairment predicted how well the patients learned to see.
These results suggest that impaired brain structure caused by aberrant early childhood experience will not fully recover after restoring typical experience later in life. Unlike the local effects of blindness on visual brain regions, the effects of poverty and adversity have often been found to be more widespread across the brain, likely because of the combined impact of the multiple biological and psychological hazards. Thus, based on our recent findings, it can be expected that experiencing harsh environments early in life results in irreversible structural changes in multiple regions of the brain, which might explain why these individuals are more susceptible to ill health, including mental disorders.
The new findings underscore the critical role of preventive measures in promoting healthy brain development in children. Ensuring access to safe environments, affordable health care, healthy food and appropriate education gives children the opportunity to develop and stay physically and mentally healthy.
This is an opinion and analysis article, and the views expressed by the author or authors are not necessarily those of Scientific American.