Fear is a universal emotion that includes everything from the decision to fight or flee to the insidious mounting of stress. It can also cause us to “freeze”, which is not an indicator of indecision in the face of fear, but stems rather from an ancestral skill used to respond to a stalker or predator. A fearful stimulus primes the body with adrenaline and prompts the fastest physical reaction possible. When the brain is triggered in fear, the autonomic system and stress hormones are activated. The amygdala gets immediate input from the thalamus and acts to start up the internal readiness and reaction system. This bypasses the cortex and any consideration of the context and such. It is just responding. In fact, the feared stimulus and the programmed response to it are indelibly etched into the amygdala, as its job is to alert the animal to dangerous, novel, and interesting situations and to direct its response.

The physical and mental responses to fear were so important to the survival of primitive man that they remain very powerful and longlasting. Unfortunately, this adaptive response is not always appropriate in today’s world. Our civilization has evolved away from the need to overrespond, but we still do. Regularly overresponding to life’s minor troubles can lead to high blood pressure, heart disease, migraines, and ulcers. Other malfunctions of the fear system are shown in disorders such as panic and phobias. Once we learn to be afraid of something, our brains become programmed to remember that stimulus in the same way, so that it’s hard to get rid of our conditioned fears.

The startle response is a good example of an adaptive fear mechanism that can sometimes get out of control. A loud, sudden noise will elicit a startle response from most people. As this type of noise is often associated with danger, it is important to be immediately alert and have the adrenaline pumping. However, if a stimulus like a loud noise is repeatedly paired with a dangerous situation, some people will develop an overactive startle response. This is often the case in PTSD. People with this disorder, war veterans or victims of abuse, startle easily and often. They suffer from physical ailments more frequently than the general population, and have an increased incidence of cancer, which is associated with a lowered immune response and raised levels of cortisol. Many of the physical and psychological symptoms associated with PTSD can be traced to the frequent, sometimes constant state of startle and hyperalertness that afflicts these individuals.

Jackie, a victim of early child abuse, was afraid of everything, from new situations to her own shadow. She was not agoraphobic or afraid of going out into the world, but nevertheless stayed at home. She always overresponded to new situations, seeing them essentially as threats, bringing with them the possibility of her being hit again.

The most poignant example of PTSD is seen in women who have been raped and cannot allow themselves to enjoy sex again. Such a woman is often indelibly programmed to be vigilant and fearful. She may consciously want to engage in sex with her mate but has an inner resistance to it. Clearly, this can cause real trouble in valued relationships.

The amygdala is the area of the brain most involved in fear. Stimuli have a direct pathway through the sensory filter of the thalamus to the amygdala, which can then mobilize the body through its brainstem connections. If you see a snake, or anything that looks like a snake, in the corner of a shadowy garage, the amygdala is immediately triggered and you react before cognizing the image. The image triggers the optic nerve to send a signal into the brain. On its way to the cortex, the signal takes a short route to the amygdala, which shouts “Emergency!” to the rest of your body, triggering a cascade of reactions: your heart rate soars, your blood pressure increases, and your senses become heightened as your body prepares to take action.

With enough time or experience, reason can stop the action. There is another, slower pathway for fear, where the information about a fearful stimulus goes from the thalamus to the frontal cortex and then to the amygdala. This occurs when you realize that the “snake” is really an old coiled garage-door spring. The response to the second pathway overrules the indication of the first. Now all systems reverse. Your blood pressure comes down and your heart rate returns to normal. The lower brain, the amygdala and the rest of the limbic system, is inhibited by the upper brain. You then begin to “think” about what just happened rather than just respond.

The two pathways can be seen as the low road and high road of fearful responses to danger. The path straight through the thalamic projections to the amygdala (the low road) is rough and crude but fast. The pathway using the cortex (the high road) gives a more accurate assessment and can be expected to lead to a more considered response, but it takes longer.

Fear responses to sudden, potentially life-threatening stimuli such as explosive noises or the attack of an animal are automatic in most people. But many other fear responses are learned. Most of us have marveled, for example, at how young children seem to have no fear of heights. We also have to teach them to look both ways before crossing the street, for fear that a car might hit them. New MRI studies also show that teenage brains may not have fully developed the reasoning pathways to adequately assess fear, which may contribute to teens’ difficulty in dealing with emotions. Neuropsychologist Deborah Yurgelun-Todd of McLean Hospital flashed forty faces showing expressions of fear to sixteen adolescents age eleven to seventeen. The younger teens reacted with heightened activity in the amygdala but only a modicum of activity in the frontal lobe. The older teens had greater activation in the frontal lobe. In previous tests, adults showed greater activity in the frontal lobe and less in the amygdala than adolescents. Apparently, there is a gradual shift of emotional and cognitive processing from the instinctive to the cognitive regions as the adolescent brain learns and grows. While this growth of wisdom or activation of the frontal cortex can help teens learn how to stay calm in stressful situations, it can also cause them to learn from parents or friends fears they didn’t have, or need to have, such as an undue fear of heights or of social situations.

As the snake example shows, fear involves contextual conditioning. A garage corner is dark, cool, and dirty, making it much more likely to be the place to find a snake than a corner of the living room. Context is a collection of many stimuli and is dependent on accurate memory of situations. The hippocampus is the brain area responsible for assessing this function. It receives processed information from the cortex that has already been associated with the context of the situation and the fearful stimulus, bringing the whole picture into perspective.

Contextual conditioning can be used in reverse to treat panic disorders and phobias such as fear of snakes, dogs, or heights. The technique, which is called “flooding,” involves a step-by-step process of gradually experiencing more and more of the feared stimulus so that the patient can learn that snakes or dogs or heights are not invariably dangerous. First the patient is asked to visualize the least fearful aspect of the experience, the snake’s interesting skin design, the dog’s cuteness, the great view from the bridge, and then to practice relaxation or meditation, which gradually lessens the anxious firing of the brain’s neurons and relaxes the tense muscles of the stomach and legs, relieving the fear input from the body. Note that both the brain and the body symptoms must be dealt with, again supporting the theory that emotions are sustained by varied systems throughout the body. Eventually the patient works up to actually experiencing the feared stimulus: holding the snake, petting the dog, standing on the bridge.

Hans Sieburg, a psychiatrist at the University of California at San Diego, has developed a virtual-reality treatment for acrophobia that he calls City Project. Patients wear high-tech goggles that provide a realistic, three-dimensional image of what it looks like to be standing on the top of a skyscraper, and while wearing them are calmed with music and reassurance. With practice in repeat sessions, they realize that they are not going to fall. Their bodies stop swaying at the sight of the ground far below. The off-balance feeling subsides. They learn with their bodies that they are not going to fall, and thus they conquer the irrational fear. They train their cortex to re-evaluate the situation and quickly respond to inhibit their amygdala.

The flooding process is straight cognitive behavioral training; it is rearranging the circuits in the brain, reducing all the neural connections that have long supported the thesis that height equals falling while strengthening the circuits that convey “safe.” By gradually rewiring, the patient begins to refocus on the fact that he’s not going to fall off the building. Separating the low (bodily) and high (cognitive) roads in this way seems to be the key to successful treatment.


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