Posts tagged: norepinephrine

Losing It

Losing it.  All of us lose “it” at some point.  The “it” appears to be the control exerted by the prefrontal cortex of the brain.  The prefrontal cortex serves many functions, and one of the most important is the inhibition of impulses.  The most common impulses to inhibit are sexual and aggressive urges; though they are not mutually exclusive.  The research of Amy Arnsten at Yale has shown that acute stress releases chemicals that reduces the influence of the prefrontal cortex over these impulses.  Not only is prefrontal control weakened, but more primitive areas of the brain emerge to pick up the slack.

In response to the stress confronting the brain, the less evolved brainstem releases two primary neurotransmitters called dopamine and norepinephrine.  Dr. Arnsten discovered that these neurotransmitters actually diminish the communication between the prefrontal area and other regions of the brain.  Once the regulatory network is down, the base of the brain sends a chemical message to the adrenal glands adjacent to the kidneys, and the adrenal releases a hormone that influences the brain in turn.  Norepinephrine and the adrenal hormone cortisol promotes emotional areas of the brain to be fearful and prepare for possible danger.

Chronic unrelenting stress may actually reduce connections between nerve cells in the inhibitory prefrontal area.  Conversely, nerve connections in the more primitive emotional areas of the brain may expand.  There is some evidence to suggest that shrinkage of neural connections in the prefrontal cortex may play a role in depression, addiction and anxiety disorders.  The neurotransmitter dopamine has been long implicated in addiction, due to its strong influence on habit forming areas of the brain.  It appears that a relatively brief exposure to stress has little lasting affect on brain structure.  The longer stress is experienced, the greater the chance the more primitive emotional brain areas will dominate one’s behavior.
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This feedback loop of the brain may play a role in post-traumatic stress disorder.  The habit forming areas of the brain allow us to quickly acquire skills and behaviors that ensure success in novel environments; for example, a war zone.  The prefrontal cortex allows us to formulate plans and inhibit fearful impulses that would reduce effective functioning.  Once the threat is removed, the dangers already experienced may overwhelm the prefrontal cortex’s ability to inhibit the emotional excitement.  Over time, the dopamine, cortisol and norepinephrine may weaken the prefrontal control to the point that the fearful impulses are rarely blocked.  The unfortunate person may re-experience highly emotional scenes in an uncontrolled and repetitive fashion.  This person would experience substantial stress in a peaceful environment, since the brain continues to assault them with feelings and images that inspire fear and avoidance.

It is still a mystery why some people manage chronic stress well, and others-not so much.  It is conjectured that some lucky people have an enhanced ability to digest the dopamine and epinephrine excreted during stress. They would possess an innate biological resistance to stress.  On the other hand, psychological research has revealed that people with a long record of mastering challenging situations are better able to tolerate stress.  People who are often defeated and overwhelmed by events are more liable to suffer with chronic stress and depression.  A person’s perception of control is a key element in the subjective experience of stress.  To what degree the subjective sense of control is a product of training or brain chemistry is anyone’s guess.  As with most psychological phenomenon, it is likely that both elements play an important role.  Effective behavioral training increases a sense of personal control; decreasing the excretion of stress chemicals.  Inheriting favorable brain chemistry may reduce the biological strength of the stress response.  Nature and nurture.  Can’t get away from it.