The optimal environment for infants and toddlers is one that is safe and predictable, with caregivers that are loving and accessible. In this environment, healthy development of the brain follows a particular sequence. First to develop are the lower regions of the brain, such as the amygdala and hippocampus. This part of the brain - also known as the reptilian brain - is dedicated to ensuring our survival, controlling functions such as our stress response. The upper regions of the brain are next to develop. This area of the brain is responsible for executive, cognitive functions, such as sensemaking or the exercising of moral judgement. Normal development of the upper regions of our brain - and, therefore, our entire physiology - requires normal development of the lower.
When the lower brain perceives a threat to survival, it floods the nervous system with danger-signaling hormones. If this happens too often, beyond a level that is normal, these hormones create immense stress, disrupting optimal sequential development of the brain. Therefore, the child that is raised in an unsafe, unpredictable environment with inconsistent caregivers, is in danger of suffering psychological and neurological disruption. At risk is any child exposed to neglect; abandonment or fear of abandonment; bullying by peers; abuse - psychological, physical, or sexual; to the witnessing of such abuse; or to any combination of the above. Exposure to such events can result in a wide variety of symptoms.