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The Neurobiology of Fear

How much of fear is inborn?

In the third book of the Harry Potter series, Remus Lupin, Harry's professor, tells him, “What you fear most of all is—fear. Very wise, Harry.” If he and Franklin Roosevelt, who said something similar before him, are to be believed, I'm a pretty darned wise person myself. Because I'm afraid of nothing more than passing on my fears to my daughter, who right now, at the age of nearly 2 years, seems to have hardly any fears at all.

Is it really possible that most of our fears are learned? Some amount of fear is required for our survival, but most of even those essential fears appear to set in only a little later in life, and by observation of fearful behaviors in adults. Scientists have found that two fears are inborn in humans—the fear of falling, and that of loud noises. Infants as young as 6 months old will hesitate and not crawl onto a surface that seems to look like a cliff edge. This early development of depth perception and avoidance of a "cliff" in humans and other animals could be an indication that the fear of heights is innate. As is the fear of loud noises. The "acoustic startle reflex" is an adaptive behavior in response to loud noises that helps protect animals from potential threats or attacks by causing a stiffening of the limbs and body wall for a short period of time, before the animal can go ahead and either fight or flee.

My daughter, let's call her Sam, has disliked the sudden noise of the pressure cooker whistle ever since she was born. She would startle, and cry, until we learned to cook more quietly when she was nearby or make sure she was far enough away. She still dislikes the sound of the blender, but is now old enough to know that it really isn't a threat. However, the startle reflex being what it is, she still cries a little when she hears the sound but is soon able to convince herself not to worry too much about it. She tries to smile through her tears when we tell her it's just the blender, and if that isn't the sweetest thing in the world, I don't know what is. But behind all this explicit sweetness and implicit fear, there's a ton going on in that tiny little brain of hers.

Nestled deep within the human brain is a tiny almond-shaped structure called the amygdala. Named after the Greek word for the nut it resembles, the amygdala seems to play an important role in coordinating the fear response.

Neural studies indicate that the unconscious evaluation of a stimulus (say, a fear-inducing one) begins before the stimulus is consciously processed. This is why, for example, our heart starts pounding faster when we hear a knock on the window in the middle of the night, and only later, once we have realized that the cause of the knocking was the branch of a tree, does the fear subside. This is also probably what's going on in Sam's brain when she "tells herself" the blender is not to be feared. The amygdala seems to be the part of the brain that intervenes between the regions concerned with the bodily expression of emotion and the areas of the brain that are concerned with conscious feeling.

As with all emotion, fear has an evolutionary basis. There seem to be some 'natural fears', such as the fear of spiders and snakes, which, although learned from cues by adults, humans seem predisposed to. Our ancestors needed to be afraid of picking up snakes or hurting them, and with time, features of our visual system that helped us detect snakes were selected and favored by evolution. It has been shown that the primate visual system responds selectively to mosaic patterns which are generally rare in nature, but common in snakes. Other fears that seem to be the result of natural selection are the fear of pointed objects and that of leopard spots.

Natural fears are fine, but what of the "unnatural" and unnecessary ones? I don't know how to swim, and thus have a little bit of an unhealthy fear of water. So when we took Sam for her first swim lesson, I was a bit concerned that my fear would show. Of course, I had absolutely no cause to fear anything, because the pool was only five feet deep! I just wanted to appear absolutely comfortable in the water so that Sam would see that and get comfortable herself. I found out soon enough that I didn't really need to worry about all that. She took to the water like a fish. All I had to do was not ruin her inborn love for water by demonstrating to her behaviors that would tell her that the water was to be disliked/feared.

The flip side to all of this, of course, is that some amount of fear (that babies might not have because of their lack of knowledge) is essential for survival. Sam doesn't know that water can be dangerous, that people could drown. She's not at an age where this can be explained to her. I thought that the baby swim lesson was excellently structured in such a way as to make the babies enjoy being in the water while introducing a few safety techniques as well. The swim instructor took care to make sure that only the necessary amount of fear was instilled in the babies, by making them sit safely on the ledge and waiting for their parents to tell them it was safe before entering the water by rolling over onto their little tummies and sliding in carefully. Let's not be so excited by the sight of water that we immediately jump in, babies!

The lack of knowledge can be a dangerous thing for a diametrically opposite reason in adults. Most of our fears are unnecessary, sometimes crippling, and usually baseless. In the British sitcom Downton Abbey, which is set in the early 20th century, one of the characters, an octogenarian set in her old ways, has her concerns about electricity. "I couldn't have electricity in the house, I wouldn't sleep a wink. All those vapors floating about," she says. She can be forgiven for this lack of knowledge, given that she lived in a pre-Google era. We no longer have that excuse (The internet of course, can be a minefield of misinformation, but that's a story for another day).

For a long time, after I read/watched something disturbing in the news, I would be a little afraid that something similar might happen to me. Not in an obvious way, but I'd startle more at noises, be a little more afraid of walking into a dark room, be afraid of going to crowded places, and so on. What happens in the brain when people are terrorized is that the conscious processing of fears is short-circuited in favor of the more autonomic fear response.

This only changed when I started taking a more statistical and logical approach to my fears. In addition to acknowledging the irrationality inherent in assuming that there's a strong correlation between something that happened in the news and my own life, I've started to ask myself a simple question—what's the likelihood of something that you're afraid of actually happening? More often than not, the answer is that the odds are infinitesimally small. Am I really going to spend my life being afraid of stuff that has very little chance of happening? What I'm doing while asking myself these questions is forcing the more "conscious" regions of the brain (parts of the cerebral cortex) to come into play.

Imaged sourced and modified from Wikimedia Commons.
Location within the human brain of the Amygdala and the Medial Prefrontal Cortex.
Source: Imaged sourced and modified from Wikimedia Commons.

In addition to arming ourselves with more knowledge about the things we fear, what is it that we can do to overcome them? (I'm assuming here that the person reading this does not have disorders related to fear such as anxiety or post-traumatic stress disorder, which require professional help).

Short of zapping our amygdalas, which seems a bit extreme, constant and scientific exposure to whatever it is that we fear seems to be what will do the trick. Rats conditioned to fear a sound that had earlier been paired repeatedly with a small electric shock had their fears reversed when the scientists played the sound repeatedly without pairing it with the electric shock. This "fear-extinction therapy" creates memories that are formed in the amygdala, but are later transferred to the higher processing centers of the brain (specifically, the medial prefrontal cortex or mPFC) for storage. These fear extinction memories in the mPFC are the ones that end up overriding the fear memories in the amygdala when fear-extinction therapy is successful. What's essentially happening is the brain telling itself, "I've been exposing myself to this fearful stimulus over and over again and nothing has happened to me, so maybe there's nothing to fear." Why waste essential neural resources on something that is not worth the time and effort?

My daughter will grow up soon enough and have a set of fears that's uniquely her own. If my husband and I equip her with the resources to be resilient and overcome her fears on her own, and teach her that fear is the only thing to be feared, we perhaps will have done our jobs.


Gibson, E. J., & Walk, R. D. (1960). The "visual cliff." Scientific American, 202, 67– 71.

John S. Yeomans, Paul W. Frankland (1995) The acoustic startle reflex: neurons and connections, Brain Research Reviews, Volume 21, Issue 3.

Snakes, Sunrises, and Shakespeare: How Evolution Shapes Our Loves and Fears by Gordon H. Orians, published by the University of Chicago Press, 2014

Kandel, E. R., Schwartz, J. H. 1., & Jessell, T. M. (2000). Principles of neural science (4th ed.). New York: McGraw-Hill, Health Professions Division.

Likhtik, E., Stujenske, J. M., Topiwala, M. A., Harris, A. Z., and Gordon, J. A. (2014). Prefrontal entrainment of amygdala activity signals safety in learned fear and innate anxiety. Nat. Neurosci. 17, 106–113. doi: 10.1038/nn.3582

More from Aditi Subramaniam, Ph.D.
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