Early exposure to trauma — extremely fearful events — and high levels of stress affect the developing brain, particularly in those areas involved in emotions and learning. The amygdala and the hippocampus are two brain structures involved in fear and traumatic stress.
The amygdala detects whether a stimulus (person or event) is threatening and the hippocampus, the center of short-term memory, links the fear response to the context in which the threatening stimulus or event occurred. These two brain structures also play an important role in the release of stress hormones such as cortisol and adrenalin influencing the capacity of the prefrontal cortex for regulating thought, emotions, and actions, as well as keeping information readily accessible during active learning.
In response to overwhelming stress in young children:
These quite concerning consequences of overwhelming stress must be considered in a larger developmental context — including aspects of the child and the availability of supportive adults.
(National Scientific Council on the Developing Child, 2005, 2007, 2010)