Brain development is much more dependent on the environment than was previously believed
The infant brain appears to be very sensitive to the emotional, social and physical environment, (1) and these environments interact with genetic endowment in a much more profound way than has been appreciated in the past. (2) Genes are important, but early experiences can alter gene expression.
The science of neuro-development has been most clearly established for vision and hearing where sensitive periods have been demonstrated in which the developing brain responds optimally to stimuli.
If the brain is not stimulated, because for example the child is deaf or not spoken to, the areas of the brain dealing with language and, in the first case all auditory stimuli, do not develop. Language can be acquired at later ages but not readily and not with the clarity that it can be acquired during the sensitive periods.
Human relationships are fundamental to healthy development
Human relationships are very important to early development, and healthy development is heavily dependent on sensitive, attuned parenting. (2) The discovery of mirror neurons (3), neurons which respond to the sight of someone else performing an action or experiencing an emotion, as well as to the performance of the action or experience of the emotion, suggests a mechanism through which this could occur.
Together with detailed observational studies, the neuro-scientific evidence would suggest that the infant brain responds to the emotions of those caring for them in a similar way as to touch, sound and sight. In this way, cerebral neurons registering a perceived emotion would replicate and the number of connections they make with other neurons increase.
So, if infants are reared in homes were parents are anxious, hostile or depressed, the parts of the infant brain registering anxiety, hostility or depression will develop, and those registering positive emotions will develop less through lack of stimulation.
Subsequently, from around age three years, processing speed increases in neural pathways that are often used whereas pathways that are not used are pruned. In this way brain development can be thought of initially as a 'call and response' affair, becoming in the third and subsequent years of life more of a 'se it or lose it' affair.
Infant brains become patterned on those around them
Although development is a two way process with infants influencing their environment as well as the other way round, the infant brain seems to become patterned on the brains of those around them. Predispositions to depression, anxiety and fear or joy, curiosity and delight seem to get neurologically modelled into the brains of infants at an early age. One particular mechanism of importance is the neuro-endocrine response to stress.
The amount of stress experienced in very early life plays a part in setting the 'thermostat' on the stress response which then determines the way the individual responds to stressful life events and their propensity to mental health problems throughout life. (4) Self-regulation is a key developmental task, enabling individuals to handle normal everyday stresses throughout life (5) and this is primarily acquired from the way sensitive parents help babies and children respond to that stress.
Although many of these phenomena are subtle and some have been demonstrated most clearly in animal studies, leaving some room for questions about applicability to human development, non-invasive investigations and observational studies have produced corroborative findings in humans. In human babies and children who experience very limited human interaction, for example those reared in profoundly neglectful orphanages, gross anatomical differences can be shown by three years of age in the areas of the brain dealing with emotion.
Gerhardt S. Why Love Matters: how affection shapes a babies brain. Hove: Routledge, 2005.
National Research Council. From Neurons to Neighborhoods: The Science of Early Childhood Development. Washington, DC: The National Academies Press, 2000.
Center on Developing Child at Harvard University, 2007. A Science-based Framework for Early Childhood Policy: using evidence to improve outcome in learning, behavior, and health for vulnerable children.
Rizzolatti G, Sinigaglia C. Mirrors and the brain: how our minds share actions and emotions. Oxford: Oxford University Press, 2008.