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12. What is the neurobiology of anxiety?

The 20th century was a watershed in neurobiology; in particular, the years 1990 to 2000 were the “decade of the brain.” To understand the neurobiology of anxiety comprehensively would require an intensive familiarity with neurochemistry and neuroanatomy.

The reader might enjoy taking a look at Joseph LeDoux’s The Emotional Brain, in which a wonderful illustration of the emotional circuitry of the brain becomes intimately connected to the way we perceive fear. LeDoux details the different inputs, conscious and unconscious, from an immediate sensory input (sight and smell) to higher thinking (“this is a stick, not a snake”) and examines their creation, neuroanatomically, of our emotional and bodily flight-or-fight response.

Several basic things show up time and again in today’s research, all of which make our work very exciting and gratifying in 2005.We know certain areas of the brain axis are highly involved in the creation of anxiety. In particular, a region called the amygdala responds to potentially dangerous stimuli by chemically arousing the body to respond immediately.

When danger is perceived to be close at hand, the amygdala’s connections to the rest of the body bypass any areas of higher thought, which make our bodies respond in a fight-or flight way.

This circuitry (called the limbic system, as in liminal, or threshold between emotion and thought), in turn, makes the memory of the particular trauma or perceived trauma indelible and codes the input of this memory on file for use in future dangerous situation assessments.

We know that chronic stress is associated with an increase in cortisol, which can result in the creation of illness or have all kinds of deleterious long-term effects on the body, making the expense of long-term anxiety quite costly to the body (in extreme panic, cortisol can flood the body and create a shock similar to surgical shock, or sudden death).

Panic disorder and posttraumatic stress disorders are the best studied in the neurobiological realm; however, many exciting areas remain for future discovery with respect to imaging and understanding the roles of all of the different neurotransmitters which the brain uses in its regulation of anxiety.

Major neurotransmitters that receive frequent mention include cortisol, epinephrine, norepinephrine, -aminobutyric acid (GABA), and serotonin. It is just as important to remember that literally hundreds of unidentified neurotransmitters make up the complexity of our thinking and feelings, as well as their connections to the rest of the body. While we may know something about the actions of any given neurotransmitter, it is still too early to know how those interactions may cascade or interface downstream with the entire “soup” of our brain chemistry.

Rick’s comments:

In the answer to one question, it is mentioned that one successful style of dealing with anxiety is humor. I’ve performed and written some comedy, so this seems to apply. I bring this up a question later because my first reaction to LeDoux’s example of higher thinking (“this is a stick, not a snake”) was: “wasn’t that the mistake that Yul Brenner made in the movie The Ten Commandments?” When I am doing something that causes me anxiety (writing, for instance) I am more likely to think in humorous or offbeat ways. When, as a youngster, some friends and I walked on a frozen lake, which terrified me, I was actually coming up with one joke after another to hide my fear. (The next time you see someone standing on a frozen lake doing a comedy routine, it’s probably me.) Now that’s neurobiology!

Terms:

Neurochemistry - the study of the mechanisms and chemical components of the nervous system, including brain structure and neurotransmitter function.

Amygdala - a part of the limbic system of the brain that is involved with learning, coordination of sensory input, and emotions.

Limbic system - the part of the brain that controls emotional responses and experiences.

Stress- a general term to describe any event or situation that raises a person’s anxiety.

Cortisol - a hormone secreted by the adrenal gland in response to stressful situations, including anxiety, fear, excitement and physical stress.

Imaging - the process of looking at parts of the human body that cannot be seen from the outside. Examples include x-rays, CAT scans and MRIs.

Neurotransmitter - a chemical Messenger in the nervous system that carries a message from one neuron to the next. Examples include serotonin and norepinephrine.

Norepinephrine - a neurotransmitter (chemical) that helps regulate mood and other physical symptoms of anxiety.

GABA - Gamma-aminobutyric acid.

A neurotransmitter in the central nervous system that is primarily involved in inhibiting impulses.

Serotonin - a neurotransmitter (chemical) in the central nervous system that is involved in many different activities, including motor function, mood regulation, and perception.

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