The brain is divided into three parts, of which the limbic system governs emotions, the cortices control rational thinking, plus a bunch of stuff in the middle and down below.
When we perceive a threat, the more primitive and quicker processing limbic system assumes executive control of the brain while the more sophisticated and slower processing cortical regions essentially go off-line.
The limbic system is also involved in a range of emotions such as what we feel when we're in love and lust.
Think of it this way: The limbic system was designed to extricate ourselves from danger long enough to experience the pleasure of a mate and thus ensure our genetic future. But what happens if our limbic system works too well? What if we perceive the entire world around us as a threat? Or, to the contrary, what if we become addicted to pleasure or novelty?
The Hariri-Caspi studies cited in Part I point to a genetic smoking gun regarding a tiny region of the limbic system called the amygdala. The amygdala is involved in fear and arousal. Think of the amygdala as a smoke alarm. For many of us, our smoke alarm works way too well. For no apparent reason, our smoke alarm sends signals to the rest of the brain.
Thus, in the produce aisle reaching for a head of lettuce, suddenly we feel the same panic as a distant ancestor of ours felt over a the presence of a tiger at the water hole.
Or, over tea and scones with people we enjoy, our brain starts acting is if we were backed into a dark alley with Jeffrey Dahmer in a bad mood.
Normally, the cortices and intermediate regions of the brain can override the limbic system and reassert control. But perhaps the signaling is coming on too strong from the limbic system. Or perhaps the signaling is too weak from the cortices. Suddenly our brain can't cope.
We may react in a variety of ways, depending on how the rest of our brain is wired. We may explode. We may say inappropriate things to people we very much care about for no apparent reason.
We may become avoidant. We freeze, unable to communicate, seeking a hasty exit.
We may feel we have to release the pressure by drinking, becoming sexually promiscuous, or violent.
We may become depressed or manic or even psychotic.
Usually, once the perceived threat has passed, we can count on our brains to reset back to normal. Scientists refer to this as homeostasis. You may have come across the term in relation to the environment. Complex systems have a way of self-organizing and maintaining a state of equilibrium.
But if we have some kind of genetic vulnerability, something different may happen. We may reach a state of allostatic overload. Our brain fails to shift back to equilibrium. Instead, we experience free-fall as our 100 billion neurons brace themselves for a hard landing. Suddenly, a good deal of the world may seem threatening most of the time.
In short, we are living in a constant state of stress. We are living in our emotions. The thinking parts of the brain are in thrall to the non-thinking parts of the brain. This applies whether we see ourselves in danger or in love. The cortical regions aren't getting through. We can't turn off the limbic system. We can't think.
In a pleasure situation, neurotransmitters such as dopamine are pumping full force, along with feel-good hormones.
In a stress situation, the dopamine is still going, but it is stoking our awareness and arousal to the point of paranoia. Meanwhile adrenaline and stress hormones are flooding the system. Our adrenaline and stress hormones prime us for fight or flight, but we have nowhere to go.
The hippocampus is also located in the limbic regions. The hippocampus has a lot to do with traumatic memory. Thus, in a stressful situation, the amygdala is likely to pull a deeply-imprinted memory from the hippocampus. Then the alarm goes off. This is why a combat veteran for no apparent reason may over-react to the sound of a car engine backfiring or why a rape victim may feel extremely uncomfortable at the sight of a face in the crowd.
The hippocampus is of particular interest due to the fact that new cell growth occurs there. Conversely, we have strong evidence of cell deterioration there and in other regions of the brain due to the effects of stress.
Basically, cells can't handle the load, Husseini Manji MD, head of the Mood and Anxiety Disorders unit at the NIMH, tells various audiences at psychiatric conferences. They atrophy and may die, thus undermining entire neuronal networks. In their weakened state, cells fail to communicate, with devastating consequences.
Robert Sapolsky of Stanford preaches a similar message. In their compromised state, he says, damaged neurons are sitting ducks for the next stressful event. We seemingly can't win.
Seven or eight years ago, Dr Manji discovered that lithium may actually assist in neuronal regeneration and growth in the hippocampus. Around the same time, Ronald Duman, PhD of Yale came up with similar findings regarding antidepressants and exercise.
These and other findings tell us that our brain systems are not permanently welded into place. Rather, the brain is plastic and in a state of constantly re-sculpting itself. It is laying down new roadwork all the time. In short, we may be genetically vulnerable, but we are not helpless.
Scientists such as Dr Manji give us reason to be optimistic about new drugs aimed at more precise targets, but that is in the way distant future. The take-home message for us in the here and now is that the brain science informs our recovery. We don't have to understand the brain science. It is enough that we simply appreciate that modern scientific discovery is validating ancient recovery practices and principles. In this context, we are talking of mindfulness coupled with stress-management. Be encouraged.