In a Toxic Environment a Brain Develops to Survive Not to Thrive

Genes provide the blueprint for early brain development, but environmental factors determine a brain’s strengths and weaknesses.

During the first few years of life, there are two major influences on the development of the brain: genes and environment. While genes provide the basic wiring of the brain, it is the environment in which a child develops that influences the direction in which the brain develops.

At the center of this developmental process is the formation of networks, or synapses, connecting specialized nerve cells known as neurons. At birth, the brain already possesses all of the neurons it will ever have. But during the next few years, the brain is developing synapses between these neurons.  More synapses are formed during this time of life than any other time. This is because the brain is feverishly processing information and gauging which areas of development are more important, based on environmental inputs.

Put simply, brain development is a process of adapting to a particular environment. Connections between neurons are formed to best respond to environmental stimuli. More developed connections, in turn, make for more efficient communication between neurons, and more advanced development within a particular sector of the brain. While the development of synapses is guided by a child’s genes, patterns of development reflect a child’s environment. In other words, the brain’s genetic blueprint unfolds in response to environmental influences.

For these reasons, early childhood experiences have life-long effects. Even within the womb, the brain and body are developing in response to their mother’s environment. When expectant mothers are dealing with stress, violence, and anxiety, the stress chemicals released by their bodies wash over their developing child as well.These developments pose life-long risks since toxic early environments can inhibit the proper function of some organs or delay cognitive, social and emotional development.

When young children develop in toxic environments, their brains naturally prioritize survival. The result is that parts of the brain associated with survival are prioritized, rather than areas of the brain that control higher order thinking and reasoning.The result is that injury is added to injury. A child born into a disadvantaged environment also will have a more difficult time learning.Recent studies show, for example, that young children exposed to high levels of domestic violence have IQs at age 5 that are up to 8 points lower than those of otherwise similar children.4

In short, for the developing brain to thrive, a child – and her family – must first be confident that they will survive.

For more information on baby brain development, please visit The Urban Child Institute here.


Gluckman PD, Hanson MA, Bateson P, et al. Towards a New Developmental Synthesis: Adaptive Developmental Plasticity and Human Disease. Lancet 2009;373:1654–7.

Groom, A., Elliot, Embleton, N., and Relton, CL. Review: Epigenetics and child health: basic principles. Arch Dis Child. Archdischild165712. Published Online First: 23 July 2010. DOI: 10.1136/adc.2009.165712.

Levendosky AA, Bogat GA, von Eye A. New Directions for Research on Intimate Partner Violence and Children. European Psychologist. 2007; 12(1): 1–5.

Koenen KC, Moffitt TE, Caspi A, et al. Domestic violence is associated with environmental suppression of IQ in young children. Development and Psychopathology. 2003; 15: 297–311.