The Source of All Fears

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Biology 202

2006 First Web Paper

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The Source of All Fears

Trinh Truong

What are fears but voices airy?
Whispering harm where harm is not.
And deluding the unwary
Till the fatal bolt is shot! Williams Wordsworth

Contrary to what Wordworth believes biologists might argue that fears are more than empty threats deluding us until our deaths. Fear serves as a purpose to caution us about the consequences of our actions as well as events in our surroundings. When we feel the presence of fear we know to be more alert, to look out and think more carefully about participating in dangerous activities. From spiders and snakes to heights and flying on planes, there is something that makes our breath a little shorter, our hearts beat faster, our palms sweaty and limbs go weak; something that makes us fearful. But sometimes these fears grow out of control and hinder us from conducting daily functions. For some people this happens more often than others, which presents the question: Why are fears better managed or conquered in some people than in others? To examine this question we must first look for the source of fear in the brain.

The part of the brain that manfactures and processes the feeling of fear is believed to be in the connections between nerves in the amygdala, a small almond structure positioned at the tip of the hippocampus. (3) Along with its important role in producing fear, it is also associated with memory learning and aggression. Research has shown that this region of the brain does not necessarily produce the response to fear but rather mediate in learning the association between a memory of harm or pain with another stimulus and sends signals to other region that will then produce the effects of fear. (1) For example, even when the amygdala is injured in rats, they will still show a fear response such as increased heart rate and breath, and release of stress hormones when they experience a shock that is associated with light. However, this fear response is not produced when the rat is only exposed to the stimulus of light associated with the shock. In a rat with a functioning amygdala, the fear response is evident simply from the light stimulus alone because the rat has learned fear from making an association between the pain of the shock and light. Still, a person could make an association between pain or harm and a stimulus but this is not necessarily fear learning itself. When people with damaged amygdala were used as subjects in the same experiment of shock and light, they were aware and able to make the connection between the appearance of light and the pain of the shock, but they did not exhibit any expressions or symptoms of fear at the exposure to the shock. The loss of their amygdala disabled them from learning fear. (1)

Just as there is a place in our brains to learn fear there is another that calms or learns to no longer be afraid of a stimulus that has once evoked fear. Research has been able to identify the prefrontal cortex as the region where fear is calmed in the brain once it is stimulated. (2) In the experiments that led to this discovery rats, conditioned to identify a tone with a shock, were presented with the tone without the shock, causing them to freeze. However, after many repeated tones without shock, the rats no longer freeze. As the rats learn to not be afraid of the stimulus the measured activity of neurons at their prefrontal cortex increased and activity at their amygdala decreased. (2) In rats with damaged prefrontal cortex the new "safety memory" is learned on the day of the experiment but never stored causing it to continually be freeze at the sound of the tone the next day. This indicated that the activity in the prefrontal cortex is able to inhibit activity in amygdala, enabling the rat to learn new memories that will inhibit their fears. The fear memory continues to be stored in the amygdala but it is prevented from inducing symptoms of fears. (4) Although there are no similar tests conducted in humans, it is believed that those with anxiety disorders have less activity in this region of their brains, in which case the amygdala's "fear memories" will overpower their prefrontal cortex "safety memories." (2) Brain-imaging has shown that in humans with posttraumatic stress disorder the prefrontal cortex is unusually smaller and less active than in normal people. (4)

Based on researches of the amygdala and the prefrontal cortex, it is safe to say that the differences in fearfulness between people lie the organization of these regions of their brain. Still we can go a little further and tracing causes of fear beyond both of these regions of the brain, and it comes down to our genes and their differences. Scientists believe that they have stumbled upon the fear gene "stathmin." which is found in high levels in the amygdala and believed to control our ability to remember and identify stimulus of fear. Mice that have been genetically engineered to be stripped of the stathmin gene have a reduced anxiety to fear stimulating situations that normal mice would respond to with fear. Although the mice lacking the gene were not less sensitive to pain than normal mice they were less sensitive to a fear stimulus linked to pain, because there was no fear memory of the stimulus and pain in their brain. (5)

Examining the sources of fear more thoroughly will perhaps enable us to develop techniques that might control our fears and help those with fear related disorders. I think there are several general approaches we can take. First of all, we can manipulate the amygdala and subdue its effects and ability to connect fear to stimulus by interferring with the neurochemical signaling among its neurons. Another option could be the prefrontal cortex, in which we will enhance its ability to inhibit the amygdala and create and store "safety memory." A third, but more controversial option would be the manipulation of our genes. However, there is a possibility that gene could produces multiple effects on the brain that we still unknown to us, and affecting it could produce unanticipated detrimental effects in other regions other than the amgydala. Although significant in understanding our fears, genetic engineering is probably not the best approach to controlling them at the moment.

These fact that a fear gene exists then suggests that we all come into this world with a predisposition for a certain level of fear. The notion that some people over-respond and some under-respond to certain situations seems to lie greatly on their genes differences. For me this new understanding of fear certainly shakes my perception about personality, character and society's conception of virtues. For example, if courage is the resistance of fear as Mark Twain says, then perhaps courage is simply a product of our genetic make up. Should society then praise someone for being courageous when it was simply pure luck that this person was born with genes that controls certain regions of his/her brain better than another? Also, should cowardice be considered shameful when it is a possibility that the person who is attributed with this trait has little control over his fear? This causes me to then question what other personality traits might simply be manifestations of genetics and to what extend people can change who they are and their personalities. Furthermore perhaps all personal traits can be traced to some genetic sequence encoded in our genes, which then organizes the neurons in a certain manner that produce a certain degree of that trait. Just as we can manipulate the chemical interactions in our body and brain to better our health and prolong our lives, we might be able to manipulate our genes to produce desirable personality traits. Whether we want to or not has yet to be disputed.

WWW Sources

1)Fear Conditioning: How the Brain Learns about Danger
2)Doctors: Front of brain control fears
3)Amygdala:Body's Alarm System
4)Fear Not:Scientists are how people can unlearn fear
5) >Scientists Face Fear Gene

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