To appreciate that, what happens to lab rats if, when they were pups, they were intermittently separated from their mothers for a while? Rats that experienced such “maternal separation” early in life are, as adults, a mess. They are more anxious, show more of a glucocorticoid response to mild stress, don’t learn as well, are easier to addict to alcohol or cocaine. It is a model for how one type of early-life adversity in humans produces dysfunctional adults, and people know tons about how each of those changes comes about in the brain.[6]
