This paper reflects the research and thoughts of a student at the time the paper was written for a course at Bryn Mawr College. Like other materials on Serendip, it is not intended to be "authoritative" but rather to help others further develop their own explorations. Web links were active as of the time the paper was posted but are not updated.
Biology 202, Spring 2005
Third Web Papers
There are events in the world that are unpleasant to experience. When a person encounters such an occurrence, there are many ways in which their brain and I-function may interpret and respond to the instance. In a world filled with natural disasters, death, war, crime, and horrendous acts of both man and nature, what is it that makes a particular experience traumatic for a particular individual? Some people live through atrocities and are able to cope with the experience in a way that does not disrupt their ability to function normally in their daily lives and move on. However, there are those that develop post-traumatic stress disorder (PTSD.) These individuals become plagued with numerous symptoms, that include vivid flashback memories, intense nightmares, irritability, exaggerated startle responses, and avoidance of situations or stimuli that may trigger a memory of the event.(1) These symptoms may dissipate fairly soon after the traumatic experience, or they may persist for the remainder of an individual's life.(2)
So what is it that determines which individuals will develop PTSD and who will not given exposure to a traumatic event? That is to say, when an individual gets a traumatic input from the external world, what is it that determines the resulting behavior? The answer to this question is quite complicated, and it involves aspects of both the brain, on a neurobiological level, and the I-function. Neither of these alone can singularly account for the determination of whether or not an individual will develop PTSD, but together they can serve to make one more or less susceptible to the disorder.
On the brain's end of things, there is strong evidence that implicates the role of genetics in the ability to recover after enduring stressful situations. It has been shown that soldiers that have higher quantities of Neuropeptide Y in their prefrontal cortex are better able to perform under stressful conditions as well as to return to normal brain functioning after the stressful conditions have ended.(3) Also linked to the topic of neurobiology is the role of the gene that codes for the production of BDNF. IT has been found in studies with animals that those who lack BDNF are more susceptible to PTSD. Similarly, animals that were genetically engineered to overproduce BDNF were resistant to PTSD (which has positive implications for potential treatments.)(4)
Another biological factor in the likelihood of being affected by PTSD occurs from the individual differences in the hippocampus.(1) It has been shown through studies that individuals with a smaller hippocampus are more likely develop PTSD. The hippocampus is linked to memory processing, and has also been implicated in the re-experiencing of traumatic events that is common of those with symptoms of PTSD.(5) It is possible that the smaller the hippocampus of an individual is, the more susceptible a person is to having particular memories stuck in the replay position, which would then in turn cause them to be symptomatic, and to then develop PTSD.
One's personality, which directly results from the I-function, also plays a role in their amount of susceptibility to PTSD after experiencing a traumatic experience. People with personalities described as compulsive or asthenic (weak) are more prone to develop PTSD. Also, people who have dealt with depression or alcoholism in the past also seem to be more likely to develop PTSD.(2) Not surprisingly, there is also a correlation between PTSD and low self-esteem. It seems possible that those who have other difficulties dealing with aspects of their life, particularly a feeling of a loss of control or low self worth are more disposed to develop PTSD. Is it that the I-function can only handle so much negativity at a time, before reaching an overload situation which results in an overactive mind (i.e. nightmares, flashbacks, and avoidance of thoughts that may trigger such?)
Age seems to also be important when assessing one's susceptibility to PTSD. While the symptoms manifest themselves slightly differently in children, it has been shown that they, too, are vulnerable to the effects of PTSD after a traumatic experience. Like adults, Children may develop PTSD after the loss of a family member, abuse, molestation, natural disasters, and any other upsetting situation.(6) Something that is particularly interesting is that within war veterans, the younger soldiers who served in combat were more likely to develop PTSD than the older soldiers.(7) It seems to me that this could arise from either biological factors or the I-function. Because brain structures are related to PTSD, and the brain changes as people age, it is possible that the changing of structures with age decreases one's likelihood of developing PTSD. It also seems possible that because when people are older they have had more life experiences, their I-function is stronger, that is, they have a stronger sense of themselves. If someone has a better understanding of who they were before the traumatizing experience, they are more likely to be able to hold on to that personality without making the experience as much a part of them as if they had a lesser sense of self.
There are important aspects of any particular event that also make a person more or less likely to develop PTSD. For example, among Vietnam Veterans that were questioned, those that had served in high war zones were more likely to develop PTSD than those who did "Theater" work. This means that the intensity of the actual event correlates to the intensity of those experiences in the minds of the veterans. And the more intense events were more likely to result in PTSD. The length of the war zone exposure was another factor that served as a predictor of the likelihood of PTSD development.(7) For individuals that were physically attacked or abused, the severity, length of duration, and number of instances of attack were also predictors in the likelihood of a victim recovering from the trauma.(1)
What I find particularly interesting are the effects that a traumatic situation may have on the neurobiology of an individual. That is, the changes that occur in the brain extend beyond the microscopic level of changing individual neurons and synapses. The changes in the brain are so extensive that they are observable on at macroscopic level. It is very interesting that the environment, that is something outside of the brain or the mind that is completely uncontrollable, has the ability to so greatly impact the functioning of entire structures in the human brain.
One of the most notable changes occurs in the prefrontal cortex (PFC) of the brain in individuals with PTSD. There is a general decrease in the activity of the PFC. In particular, there is a decrease in the amount of benzodiazepine binding in the medial prefrontal cortex (mPFC). This results in an increase of activity in the amygdala, which plays a key role in the process of assessing situations to determine whether or not a fear response is warranted.(8) The change in the activity of the amygdala could account for the heightened sense of fear and hyper vigilance that occurs as a symptom of PTSD. Another change in brain activity that results from the changes to the PFC results from the loss of the ability of the PFC to serve as an inhibitor. The mPFC acts in a way to inhibit the dorsal raphe nucleus, which is the region of the brainstem that is primarily accountable for causing alarm in a situation in which it is necessary. The mPFC has the capability of executively deciding when a situation requires alarm, more specifically it determines if the situation is controllable or not. By losing the ability to inhibit the brainstem, the mPFC loses the ability to calm the individual by removing the sense of alarm, which could also contribute to the symptoms of PTSD.(9)
Something that I found particularly interesting is that when an individual experiences something horrendous and develops PTSD, their hippocampus actually gets smaller.(5) This means that not only are individuals with small hippocampuses more likely to acquire PTSD, but also that PTSD can cause the hippocampus to get smaller. Clearly there is a strong link between the two, and I think that more research on the specific interactions between the hippocampus and traumatic experiences ought to be completed.
Other neurobiological alterations that result from traumatic experiences in individuals with PTSD involve hormones and neurotransmitters, which have been shown in a variety of instances to alter behavior. Levels of cortisol, a hormone, are especially low in individuals with PTSD due to the abnormal activity of the HPA.(4, 5) This tends to have important health implications such as increased susceptibility to physical ailments (such as gastrointestinal problems and circulatory-related diseases.)(10) Levels of epinephrine and norephinephrine are unusually high in individuals with PTSD, which have been linked to changes in emotional state.(4, 5) As a result, the environmentally caused changes on the brain result in changes of the I-function.
There are other ways in which the I-function may become altered as a result of PTSD or the traumatic situation itself. During times of extreme crisis, a person may act in ways that they do not consider to be consistent with the idea that they hold of themselves. They may experience cognitive dissonance and have an altered sense of self because of their actions in one particularly extreme situation, one which is not a part of their daily lives or normal existence.(11) The I-function can also be greatly impacted in those individuals that experience a chronic condition of PTSD. Because the condition can persist for months, years, or even a lifetime,(2) an individual may experience a subsequent personality change as a result of the continued symptoms so that the sense of self includes the altered state.
Because the mind, brain, and body are all affected in an individual with PTSD, it is important to take each into consideration when treating a patient with this disorder. The two main approaches to treating patients currently consist of a variety of drug treatments as well as various cognitive-behavioral therapy techniques. Cognitive-behavioral therapy (CBT) can encourage one to think reflectively about their traumatic experiences and their resulting behaviors and emotions. Some specific therapy methods include teaching relaxation techniques or examination of one's morals and values. Therapy may be in a one-on-one situation, family therapy, or group therapy. This enables one to focus on their individual situation, their interactions with their family members as a result of their PTSD, or their working with others to realize that they are not alone in their circumstances respectively.(12) Notably interesting is that CBT is thought to improve function in the PFC(8), thus altering the brain in a way so as to counteract the effects of PTSD on the PFC. Prescribed medications have been found to alleviate particular symptoms in some individuals. Most of them work by increasing or decreasing levels of particular neurotransmitters in the brain (e.g. SSRIs.) There are medications that are especially effective for treating symptoms of depression, anxiety, and sleep disorders.(12) While I'm not sure of any studies with humans, it has also been noted that exercise in mice increases levels of neurotransmitters and relieves some of the symptoms of PTSD as well.(4) The National Center for PTSD has suggested that cognitive-behavioral therapy appears to be more effective than drug therapy(5), but it seems to me that a combination of both may be more effective. Medications can ease the troubles of the brain while therapy eases the troubles of the mind (and going for a run may help, too.)
Although there is knowledge that there are many ways in which the mind, brain, and external (traumatic) experiences interact, there is still much to be known about the details of the interactions. We know that there are genes that make a mind interpret an experience as too traumatic to handle. But what exactly is it about a given mind, (or even a given gene) that makes the mind work that way? Once we have more insight into the workings of the mind and the brain, that is once we know more than just mechanics of structures, we will have more insight into the causes and implications of post-traumatic stress disorder.