Childhood Adversity and Brain Development
Thus, childhood adversity can atrophy and blunt the functioning of the hippocampus and frontal cortex. But it’s the opposite in the amygdala— lots of adversity and the amygdala becomes larger and hyperreactive. One consequence is increased risk of anxiety disorders; when coupled with the poor frontocortical development, it explains problems with emotion and behavior regulation, especially impulse control.
Sapolsky, Robert M.. Behave: The Biology of Humans at Our Best and Worst (p. 251). Penguin Publishing Group. Kindle Edition.The worst stressor seems to be an abusive mother, or being separated from the mother at an early age, but all sorts of other adversity (poverty, lead poisoning, etc.) seem to have similar results.