Searching the Brain for the Roots of Fear

You are taking a walk in the woods ― pleasant, invigorating, the sun shining through the leaves. Suddenly, a rattlesnake appears at your feet. You experience something at that moment. You freeze, your heart rate shoots up and you begin to sweat ― a quick, automatic sequence of physical reactions. That reaction is fear.

A week later, you are taking the same walk again. Sunshine, pleasure, but no rattlesnake.  Still, you are worried that you will encounter one. The experience of walking through the woods is fraught with worry. You are anxious.

This simple distinction between anxiety and fear is an important one in the task of defining and treating of anxiety disorders, which affect many millions of people and account for more visits to mental health professionals each year than any of the other broad categories of psychiatric disorders.

Scientists generally define fear as a negative emotional state triggered by the presence of a stimulus (the snake) that has the potential to cause harm, and anxiety as a negative emotional state in which the threat is not present but anticipated. We sometimes confuse the two: When someone says he is afraid he will fail an exam or get caught stealing or cheating, he should, by the definitions above, be saying he is anxious instead.

But the truth is, the line between fear and anxiety can get pretty thin and fuzzy. If you saw the abovementioned snake at a particular rock on the path of your walk, and are now at that spot, the rock may stand in for the snake and elicit fear, even though the snake itself is nowhere to be found.  In modern life, many fear states are like this — they are brought on by things, signposts or signals that stand for harm rather than things that are truly harmful.  After the Sept. 11 attacks, for instance, many New Yorkers felt uneasy at the sound of low flying airplanes.

How do things come to symbolize threats?  Remember Pavlov’s dog?  When the bell rang the dog salivated because the bell had previously been rung as the dog was being fed (actually, it wasn’t a bell, but no matter).  The dog’s brain formed an association between the sound and the food, and the sound came to elicit salivation in preparation for the imminent food. As the snake and Sept. 11 examples above illustrate, the same thing happens in dangerous situations.

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We actually know a tremendous amount about what goes on in the brain when stimuli present during danger become memory triggers for the danger.  To make a complicated story very simple (though not inaccurate) a region in the brain called the amygdala connects the two events, forming an unconscious memory of the association.  When the neutral stimulus (the rock or the sound of an airplane) later occurs, it automatically activates the amygdala like the original danger did, eliciting fear, and also triggers worry — anxiety.  The automatic nature of the activation process reflects the fact that the amygdala does its work outside of conscious awareness.  We respond to danger, then only afterward realize danger is present.

Every animal (including insects and worms, as well as animals more like us) is born with the ability to detect and respond to certain kinds of danger, and to learn about things associated with danger.  In short, the capacity to fear (in the sense of detecting and responding to danger) is pretty universal among animals.  But anxiety ― an experience of uncertainty ― is a different matter. It depends on the ability to anticipate, a capacity that is also present in some other animals, but that is especially well developed in humans.  We can project ourselves into the future like no other creature.

While anxiety is defined by uncertainty, human anxiety is greatly amplified by our ability to imagine the future, and our place in it, even a future that is physically impossible.  With imagination we can ruminate over that yet to be experienced, possibly impossible scenario. We use this creative capacity to great advantage when we envision how to make our lives better, but we can just as easily put it to work in less productive ways — worrying excessively about the outcome of things. Some concern about outcomes is essential to success in meeting life’s challenges and opportunities. But at some point, most of us probably worry more than we need to.  This raises the questions: How much fear and worry is too much? How do we know when we have skipped the line from normal fear and anxiety to a disorder?

Fear and anxiety are in the brain because they helped our ancestors and theirs cope with life’s challenges. But when these states interfere with our ability to survive and thrive, one has an anxiety disorder. These include phobias, panic disorder, post-traumatic stress syndrome, generalized anxiety disorder, among other conditions. While fear plays a key role in some anxiety disorders (phobia, post-traumatic stress), it takes a back seat in others (generalized anxiety).

Pathological fear and anxiety are due to alterations of the brain systems that normally control fear and anxiety (structures such as the amygdala).  A tremendous amount has been learned about the normal system from studies of other animals. This gives us a good shot at understanding the pathological forms, and developing ways to treat and maybe even prevent them. Indeed, recent research in animal models are giving us new clues about how to treat problems of fear and anxiety in humans, both pharmacologically and behaviorally, and helping us figure out how we can pull people back once they’ve crossed the blurry line.

BONUS TRACK

It’s been proposed that the poet Emily Dickinson suffered from severe anxiety.  In her series of poems, “Part 1, Life, XCVIII,” she writes: “While I was fearing it came, But came with less of the fear, Because that fearing it so long, Had almost made it dear.”  I took her lyrics from this poem and used them as the basis for a rock song about anxiety.  It’s called “Fearing,” and is appears on the second CD by my band, The Amygdaloids. Our songs, which are mostly original works, are about mind and brain and mental disorders.  Here is a music video of “Fearing” that includes two mini lectures on the pathological states such as those suffered by Dickinson.

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Joseph LeDoux is a Henry and Lucy Moses Professor of Science, and professor of neural science and psychology at New York University. He is also the director of the Emotional Brain Institute. He is the author of many articles in scholarly journals, and the books “The Emotional Brain: The Mysterious Underpinnings of Emotional Life” and “Synaptic Self: How Our Brains Become Who We Are.”