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Biology 202
2002 Third Paper
On Serendip

Phobias and the Brain

Miranda White

You are in an airport waiting for your plane to arrive. You've never flown before, and are more terrified than you can ever remember being. Everyone has told you the supposedly comforting statistics - "millions of planes take off each day and there's only a handful of crashes," "flying is safer than driving." You know rationally that there is no reason to be so scared, but regardless your heart is racing, your palms are sweating, and you're light-headed. Simply the thought of being up in the air, out of control, makes you feel faint. Finally the flight attendant announces that your plane has arrived. But as all the other passengers line up to get onboard, you grab your luggage and walk straight out of the airport, with every step feeling more and more relieved. What is this feeling of anxiousness? Why can't you get rid of it even though you consciously know that it is irrational? What is it caused by? How can it be prevented or lessened?

What you experienced in the airport is a phobia. A phobia is the sensation of extreme fear "when it is not justified by the presence of any real danger or threat, or by any rational cause, and when it is accompanied by a systematic avoidance of the situations that lead to it." (1) A phobia is brought on by a specific stimulus or situation, for example, insects, heights, crowds, or the dentist. Presentation with the fear-inducing stimulus causes a severe anxiety response with very apparent and specific physical manifestations, such as a rapid heartbeat, shortness of breath, trembling, and sweating. Most individuals suffering from phobias are able to recognize that their fear is fundamentally irrational, yet nonetheless go through great lengths to avoid any contact with the given stimulus. (2) Somewhere between 5.1% and 12.5% of Americans have experienced some sort of phobia. (3) Women are two to three times as likely to have phobias than men. There are three basic kinds of phobias: agoraphobia (fear of situations in which escape may be difficult), social phobia, and specific phobias. The DSM-IV has separated phobic stimuli into four basic categories: animal, situational, blood injury, and nature-environment. (3)

Though the experience of phobias is relatively common and their physical characteristics are generally well understood, there is no real consensus on the neurobiological basis of phobias. Instead, there are currently several different models and theories that work to try to understand how and why phobias occur in the human brain. Most hypotheses regarding phobias take a different approach, from biological to psychoanalytic to evolutionary. Is there one model that seems "less wrong" or more satisfying in our efforts to understand the biology of phobias? Using the various models, how do phobias seem to come about? How does thinking about phobias add to our understanding of the brain and behavior?

The classical conditioning model was one of the first theories used to describe phobias. Many years ago, scientists observed that one could willingly elicit a fear response in an animal or human through systematic teaching. For example, if every time a rat is presented with a low buzzing noise, it is electrically shocked, eventually, when it hears the noise alone (with no shock), it will exhibit symptoms of fear. (3) Scientists used to think that people were similarly conditioned to fear the phobic stimulus. In other words, individuals at some point in their lives experienced a negative event with their phobia and so learned to fear it. Though ostensibly a good explanation for the exaggerated fear response exhibited in phobic individuals, with closer scrutiny, this theory proves to be problematic.

Most people do not recall having an initial negative interaction or trauma associated with their phobia. Similarly, there are many cases in which patients have, without a doubt, never come in contact with their phobic stimulus. For example, many people who have flying phobias have never actually been on a plane. In fact, almost half of all phobic people have never had a painful experience with the object of their fear. (4)) In addition, a very small number of stimuli comprise the majority of phobias. In the same way, not all individuals who are presented with a fear-inducing stimulus develop phobias. (3))

Others believe that phobias exist because of evolutionary development to avoid danger in order to improve survival. There are several stimuli that are shared by the most phobic people (heights, insects, crowds, etc.) These phobias, with a couple of exceptions, relate more closely to pre-technological societies. Thus, some scientists, such as Martin Seligman, believe that people are inherently "prepared" to fear certain objects. ((5))) In other words, our phobias relate closely to the perils of our ancestors, as through natural selection, those who feared the dangerous stimulus survived while those who didn't, died off. Prepared fears appear to be very easily conditioned. Some scientists, such as LeDoux, believe that preparedness and the ease of conditioning are the result of certain preexisting neurological connections that exist evolutionarily. These connections are turned on with relative ease.

The most convincing evidence in support of the evolutionary model of phobias is provided by fear conditioning experiments using rhesus monkeys. Wild rhesus monkeys fear snakes while domestic rhesus, unless conditioned, do not. In the experiment, domestic rhesus monkeys are shown a video in which peers respond fearfully to both snakes (fear-relevant stimuli) and flowers (neutral stimuli). When exposed to the two stimuli, the monkeys all exhibited a fear response to snakes but not to flowers. (6) Thus it seems that there is a pre-existing pathway that causes the fear of snakes to be easily turned on by simple conditioning. Interestingly, if this hypothesis holds true, we must have an altered concept of phobias and phobic individuals. Phobias are clinically defined as irrational fears. Yet, evolutionarily, they appear to be extremely realistic, having their roots in very real dangers. Nonetheless, all evidence regarding the evolutionary preparedness hypothesis remains largely speculative.

Many people have turned to the brain in order to understand the biological circuitry behind phobias. The amygdala, an almond shaped nuclear complex that is located in the dorsomedial portion of the temporal lobe, has been proved to be intricately tied in with the brain's perceptions of fear. A portion of the amygdala known as the lateral nucleus is particularly responsible for fear responses. The amygdala receives afferent projections from such areas as the olfactory system, the hypothalamus, the cerebral cortex, and the brain stem. It projects efferent signals to the dorsal thalamus, the cerebral cortex, and brain stem. (7)) There are many more circuits leading from the amygdala to the prefrontal cortex than the other way around, causing us to have so little control over our fears.
LeDoux proposed a hypothesis regarding fear conditioning and the brain that has been well accepted by the science community. There are two separate neurological pathways that account for the ability of animals to be conditioned to fear objects. The two circuits, both activated by a conditioned stimulus, have different functions and destinations in the brain. One pathway leads from the sensory thalamus to the amygdala and the other pathway goes through the sensory cortex. The former provides rapid, imprecise information in order to ensure a quick response if necessary. It allows for the formation of emotional memories in the amygdala. (3)) The latter pathway (from the sensory cortex) takes more time, but generates a more detailed understanding and representation to the amygdala. This pathway permits the brain to liken one situation to a previous encounter in order to respond most effectively. This circuit is tied with the hippocampus in order to form clear fear-related memories. Thus, in theory, the two pathways should work together to create the most accurate and rapid response to danger. (8))

But what goes wrong in the pathways of phobic individuals? Why do their brains seem to react to harmless situations as if they were lethal? Is this phenomenon explicable using this model? Changes in the processing abilities of the amygdala may have a profound effect on the processing of fear. "Lesions of the amygdalar central nucleus interfere with every measure of controlled fear, including physiological and behavioral responses." (9)) There is evidence that amygdala and hypothalamic damage may be the cause of phobias. For example, phobic children are born with a decrease in the activation of the neurons in their amygdala and hypothalamus. Abnormalities in the hippocampus and the medial prefrontal cortexes may also be the cause of phobias. Damage to the hippocampus has a strong effect on memory, and thus could cause an individual to incorrectly remember a fearful event. The medial prefrontal cortex is associated with the phenomenon of extinction, the weakening of a fear response to a conditioned stimulus over time. Thus, damage to this region could allow for the persistence of a fear response for years after an initial encounter with the stimulus (even when the individual is repeatedly shown that the stimulus is in fact harmless).

Genetics may also play a role in the formation of phobias. There is recent evidence that phobias might be linked to a mutation in chromosome 15. This defect may make people more susceptible to developing phobias. It is thought that phobic individuals are born with the mutation, but it doesn't manifest itself until later in life. (10)) Personality traits may also play a role in the formation of phobias. On the other hand, some believe that phobias are the result of one's culture. Some phobias are much more prevalent in some societies than others. For example, a person is much more likely to suffer from agoraphobia in the United States than in Mongolia. Similarly, only Japanese suffer from a phobia called taijin kyofusho, the fear of offending others through one's social incapability. (4))

There are various ways to go about treating phobias. One of the most effective cures is behavior therapy (otherwise known as exposure therapy.) In behavior therapy, a patient and therapist systematically confront the feared stimulus until the patient becomes desensitized to it. One type of exposure treatment is called flooding. Flooding is a therapeutic technique in which the phobic individual is exposed to their feared object or situation for an extended period of time. Eventually, the fear response will fade as the person sees the irrationality behind their phobia. Another method is called modeling, a technique in which a patient watches another person face their phobia and thus vicariously learns that their phobia is truly harmless. Many therapists also use relaxation and hypnosis to cure their patients of phobias. Relaxation training involves teaching the patient to be aware of the physical symptoms of their phobia (increased heart rate, muscle tension, etc.) and to, if possible, eliminate them. Another form of treatment is cognitive therapy, a technique in which people are taught to "think differently." Patients are made aware their fears are unrealistic, harmful, and meaningless. (11)

More recently biomedical drugs have been commonly used to control the panic and lessen the anxiety of phobias. Some medications are used to lessen the physical responses associated with phobias. Benzodiazepine anti-anxiety agents, such as Xanax and Valium, are used in short-term situations to treat phobias. Doctors also prescribe beta-blockers to diminish the performance-inhibiting fear response. Other common phobia treatment drugs include serotonin specific reuptake inhibitors (Prozac, Paxil, Zoloft) along with other antidepressants. (12)) Interestingly, in a study done on the brains of patients who underwent various forms of phobia treatments, both biomedical drugs and behavioral therapy alter brain functioning in the exact same way, as the two treatments caused a decreased blood flow in the amygdala and the hippocampus. (13))

In the future, scientists should try to gain more concrete, biological knowledge about the origins of phobias in order to produce the most effective treatment possible. Doctors should make use of imaging techniques, such as MRIs, CT scans, and PET, in order to better understand the brains of phobic patients and see if there are actual differences between phobic and non-phobic individuals. In addition, neurobiologists might conduct research to better understand the processes by which phobias come into existence, in particular the interaction of a vulnerable brain and a particular experience that coalesce into a phobia. By doing so, it may be possible to come up with forms of prevention, not just treatments.

Though these different models and treatments of phobias do not allow for a conclusive or single biological understanding, they do bring up some very important questions about the brain. Each model seems to indicate differing brain functions and pathways that cause phobias. Thus the question of what exactly makes a phobia happen remains unanswered. But it is quite possible that phobias exist in different people for different reasons. Therefore, perhaps is it most accurate to understand phobias through seeing a coexistence of all the different models. Phobias are very much related to the issue of brain and behavior. There seems to be a clear parallel between the pathways in the brain and a person's behavior. It is clear that phobias originate in the brain yet they resonate loudly in the body, strongly influencing one's behavior. But at the same time, in some treatments, for example flooding, alterations in patients' behavior cause clear changes in brain functioning. For me, this helps prove that the brain and behavior are one and the same.


1)Phobias: When Fear is a Disease

2)American Psychiatric Association, a comprehensive look at the different kinds of phobias

3) Fyer, Abbey J. Current Approaches to Etiology and Pathophysiology of Specific Phobia. Society of Biological Psychiatry, 1998.

4)The Phobia List Categories

5)Website that Deals With Preparedness

6)Evidence for Preparedness Theory

7)Anatomy of FearThe Biology Related to Fear and the Amygdala

8) Ledoux, Joseph. Fear and the Brain: Where Have We Been, and Where Are We Going? Society of Biological Psychiatry, 1998.

9)Personality Correlates to Memory Change

10)The Link Between Phobias and Genetics

11)A Page of Various Treatments for Phobias

12)General Information of Phobias

13) Fumas, Tomas Common Changes in Cerebral Blood Flow in Patients with Social Phobia Treated With Citalopram or Cognitive-Behavior Therapy. Arch General Psychiatry. Vol. 59, 2002.

14)Terms relating to phobias

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