This is the fourth in our conversation on past trauma. Last week, we looked at the brain in a state of siege, which is what happens when we are raised in highly stressful environments, such as poverty and abuse. Through a series of complex biological processes, our brain cells get worn down to the point where they can no longer handle the next stressful event. Eventually, whole brain systems are compromised, resulting in the underperforming thinking parts of the brain failing to modulate the overwhelmed reactive parts of the brain.

The outcome is fairly predictable: Anxiety, depression, mania, psychosis, behavioral problems. Essentially, the biology of trauma and chronic stress is the biology of mental illness, of a battered brain no longer capable of coping with its environment. 

“Okay” says Tabby, responding to last week’s post, “that still doesn't explain why multiple siblings, within the same household, raised in the same environment do not ALL have ‘overly sensitized’ systems.”

Some siblings growing up in the same environment, she goes on to say, turn out just fine while others struggle. What gives?

In essence, what Tabby is asking is why some brains are more biologically resilient than others, why some individuals can “snap out of it” while others cave in. Let’s look at the resiliency/vulnerability issue from three different and overlapping perspectives: Genetics, epigenetics, and development. All three involve environment in the equation. 

Genetics

In 2002-2003, researchers from the NIMH and other centers published a series of eye-opening studies that - in response to stressful situations - linked certain gene variations to heightened responses in certain parts in the brain and in turn to emotions and behaviors such as fear and depression and aggressive behavior. For instance, one study - cited many times in my posts here on HealthCentral - found that those with the “short allele” to a certain gene had a far greater tendency to depression when exposed to a recent series of stressful events. (Caspi et al, "Influence of Life Stress on Depression: Moderation by a Polymorphism in the 5-HTT Gene," Science, July 18, 2003.)

The “short-allele” people, in essence, represented a population that was genetically vulnerable to mental stress and thus prone to depression. The “long-allele” people, by contrast, proved resilient. 

This makes obvious sense when we think of our various vulnerabilities and resiliencies regarding all manner of physical stresses, such as to pain, allergens, certain types of food, bacteria and viruses, and on and on and on. But wait, the picture gets more complicated ...

Epigenetics

The gene studies from ten years ago forcefully demonstrated that mental illness involves a complex dynamic between genes and our environment. Our genes may predispose us to depression or bipolar, for instance, but grow up in the right environment, free from trauma and abuse or resilient to stress, and perhaps these genes never get switched on.