Biological Roots of Anxiety

This article reviews some of the biological roots of anxiety, as well as the consequences of chronic stress on health. Most people with anxiety describe uncomfortable physical symptoms that go along with their worries. They may experience heart palpitations, nausea, dizziness, sweats, or muscle tension. Those symptoms are evidence that anxiety is truly a disorder of both the mind and the body.

The anxious brain

The brain takes in information about the world through sight, taste, smell, sound, and touch. Constantly scanning the world for meaning, the brain integrates information from the past with the present and plans what actions to take. For most people, most of the time, the brain does a pretty good job. But for those with chronic anxiety, something goes awry.

Billions of nerve cells (neurons) reside in the brain. They’re organized into a variety of complex structures or circuits. Some of these structures are particularly involved in producing feelings of anxiety, fear, and stress. These brain structures communicate with one another by sending chemical messengers, known as neurotransmitters, back and forth among them.

In the following sections, we explain how the brain interprets information and what role the brain’s chemicals play in making you anxious.

How the brain’s circuits connect

Think of the brain as having many interconnected circuits. One circuit involves both the limbic system and the frontal lobes. To keep it simple, the limbic system is a primitive region of the brain and is responsible for immediate reflexive responses to threat. The thalamus and the amygdala form part of the limbic system. The frontal lobes, which handle judgment and reasoning, respond more slowly and thoughtfully.

When the brain perceives something as being dangerous, it immediately registers in the brain’s control center known as the thalamus. The thalamus rapidly sends a signal directly to the amygdala, which activates reflexive fear responses. Those responses prepare the body to fight or flee. The thalamus also delivers a warning signal through the frontal lobes. The frontal lobes, where rational thought occurs, take a little more time and use reason and logic to determine the veracity of the incoming threat. That’s why when you perceive something as being scary, your body immediately responds with a rapid heartbeat, tension, and dread. If and when the rational frontal lobes figure out that the scary thing actually doesn’t pose a significant threat, you calm down. That’s the way the brain is supposed to work.

For example, around the Fourth of July you hear loud popping sounds. Your limbic system may initially interpret those as gunshots, but your frontal lobes take a few seconds longer and conclude that the sounds are likely to be firecrackers. However, dogs, who don’t understand calendars or have well-developed frontal lobes, remain fearful.

In anxiety disorders, either the limbic system or the frontal lobes (or both) may fail to function properly. Thus, the limbic system may trigger fear responses too easily and too often, or the frontal lobes may fail to use logic to quell fears set off by the limbic system. When the brain signals danger, the body responds by getting ready for action. The next section explains the chemical aspects of fear.

Neurotransmitters

Neurotransmitters help nerve cells communicate feelings, fears, emotions, thoughts, and actions through an intricate orchestration. Four major neurotransmitter systems and some of their functions include

• The noradrenergic system, which produces norepinephrine and epinephrine. It also stimulates organs required in the fight-or-flight response (see the following section).
• The cholinergic system, which activates the noradrenergic neurotransmitters and facilitates formation of memories.
• The dopaminergic system, which is involved in movement and is also related to feelings of pleasure and reward. Dopamine disruptions cause problems with attention, motivation, and alertness, and appear to be quite important in the development of fear responses.
• The serotonergic system, which is related to moods, anxiety, and aggression.

As these neurotransmitters pulse through your brain, the brain circuitry involved in fear and anxiety lights up. Your body then responds with a full-system alert known as the fight-or-flight response.

Preparing to fight or flee

When danger presents itself, you reflexively prepare to stand and fight or run like you’ve never run before. Your body mobilizes for peril in complex and fantastic ways. This figure gives you the picture.

Your body responds to threats by preparing for action in three different ways: physically, mentally, and behaviorally.

• Physically: The brain sends signals through your nervous system to go on high alert. It tells the adrenal glands to rev up production of adrenaline and noradrenaline. These hormones stimulate the body in various ways. Your heart pounds faster and you start breathing more rapidly, sending increased oxygen to your lungs while blood flows to the large muscles, preparing them to fight or flee from danger.

Digestion slows to preserve energy for meeting the challenge, and pupils dilate to improve vision. Blood flow decreases to hands and feet to minimize blood loss if injured and keep up the blood supply to the large muscles. Sweating increases to keep the body cool, and it makes you slippery so aggressors can’t grab hold of you. All your muscles tense to spring into action.

• Mentally: You automatically scan your surroundings intensely. Your attention focuses on the threat at hand. In fact, you can’t attend to much of anything else.
• Behaviorally: You’re now ready to run or fight. You need that preparation in the face of danger. When you have to take on a bear, a lion, or a warrior, you’d better have all your resources on high alert.

Granted, in today’s world, you’re not very likely to encounter lions and bears. Unfortunately, your body reacts too easily with the same preparation to fight traffic, meet deadlines, speak in public, and cope with other everyday worries.

When human beings have nothing to fight or run from, all that energy has to be released in other ways. So you may feel the urge to fidget by moving your feet and hands. You may feel like jumping out of your skin. Or you may impulsively rant or rave with those around you.

Most experts believe that experiencing these physical effects of anxiety on a frequent, chronic basis doesn’t do you any good. Various studies have suggested that chronic anxiety and stress contribute to a variety of physical problems, such as abnormal heart rhythms, high blood pressure, irritable bowel syndrome, asthma, ulcers, stomach upset, acid reflux, chronic muscle spasms, tremors, chronic back pain, tension headaches, a depressed immune system, and even hair loss. The following figure illustrates the toll of chronic anxiety on the body.

Before you get too anxious about your anxiety, please realize that chronic anxiety contributes to many of these problems, but we don’t know for sure that it’s a major cause of all of them. Nevertheless, enough studies have suggested that anxiety or stress can make these disorders worse to warrant taking chronic anxiety seriously. In other words, be concerned, but don’t panic.

When people perceive danger, their most common response is to fight or flee. However, sometimes there is another reaction — freezing. This response is common in animals but less understood in humans. The well-known phrase “like a deer caught in the headlights” is an example of a freeze response. During this state, heart rate actually decreases, and the body becomes immobilized.

Usually, this freezing state is brief and can immediately change to fight or flight. This phenomenon explains why some people freeze during an emergency or find themselves unable to respond in a threatening situation. However, not as much is known about the human freeze response, and more research is needed to explain the nuances of why and when this occurs.