Biology 202

2006 First Web Paper

On Serendip

We all have felt depressed at one time or another in our lives. However, there are individuals that experience this very same feeling over much longer periods of time. Clinical and major depression is characterized by an array of symptoms that primarily deal with a change in one's behavior. If Emily Dickinson's theory of brain being analogous to behavior is in fact true, this would mean that a change in the brain would trigger individuals to behave in the manner they do. However, this notion is not necessarily supported by what some believe to be causes of depression. In that, the behavior of a depressed individual may solely have to do with environmental factors that don't necessarily change the brains composition or circuits. Most studies and evidence I have come across show this is not the case and that the brain does indeed equal behavior in the case of depression.

Major depression is growing in all different age groups, crossing all borders of different backgrounds and ethnicities. Even the president of the United States is on anti-depressants. (2)
At the rate of increase, it will be the 2nd most disabling condition in the world by 2020, behind heart disease. (1).

Being clinically depressed is quite different from just feeling down. It is considered an actual disease. Many different depressive episodes exist and can last for months, and even years. This state of mind can interfere with your social and work and overall functioning. It is usually characterized by at least five of the following symptoms that represent a change in lifestyle, and thus behavior: having a depressed mood most of the day, almost everyday, a decreased interest or pleasure out of all, or almost all, activities, a significant weight loss or weight gain –or just an increase or decrease in appetite nearly everyday, insomnia or sleeping too much, fatigue or loss of energy nearly everyday, feelings of worthlessness or excessive or inappropriate guilt, diminished ability to think or concentrate, or indecisiveness, and recurrent thoughts of death, suicidal idealation or an actual suicide attempt. (1)

The actual basis of depression is unknown but it may be attributed to and influenced by genetic, environmental and neurobiological factors. Perhaps, the biggest debate on what causes depression is based on a debate on whether neurochemical imbalances or environmental influences such as unfortunate events, certain life experiences or negative thinking cause depression.

Many brain chemicals, neurochemicals (such as nonrepinephrine) and hormones have been linked to the development of depression. Monoamine depletion is most often the disturbance that is commonly detected in depressed individuals. Serotonin, norepinephrine, and dopamine have been identified as the main trigger causing components in depression with serotonin and norepinephrine being evidenced as the more prevalent of the bunch. "Among the findings linking impoverished synaptic norepinephrine levels to depression is the discovery in may studies that indirect markers of norepinephrine levels in the brain-levels of its metabolites, or by-products, in more accessible material are often low in depressed individuals. In addition, postmortem studies have revealed increased densities of certain norepinephrine receptors in the cortex of depressed suicide victims" (3)

Deficiencies in the serotonin 5-HT system are observed in depressed individuals as well. These depletions may interact with and may be responsible for falls in norepinephrine levels mentioned above. Serotonin secretion may also account for the emotional, appetite, libido, and sleep disturbances associated with depression. (3)

Hormonal abnormalities may also characterize the depressed brain especially those caused by the release of an excessive amount of stress hormones. The most significant irregularity lies in the hypothalamic-pituitary-adrenal (HPA) axis, the system that manages the body's response to stress. When a threat to physical or psychological well-being is detected, the hypothalamus increases production of corticotropin-releasing factor (CRF), which, in turn, induces the pituitary to secrete adrenocorticotropic hormone (ACTH). ACTH then instructs the adrenal glands to release cortisol. Thus, chronic activation of the HPA axis may result in illness and depression. (3)

Some attribute these neurochemical abnormalities to be caused by genetic factors providing support for the theory that brain does indeed equal behavior. As your genes may carry information to cause your brain to alter your behavior. It has been found that depression and manic-depression frequently run in families. Thus, close blood relatives (children, siblings and parents) of patients with severe depressive or bipolar disorder are much more likely to suffer from those or related conditions than are members of the general population. This observation was largely made by studies of identical twins and fraternal twins support an inherited component. For example, if one identical twin suffers from depression or manic-depressive disorder, the other twin has a 70 percent chance of also having the illness. (4).

Then there is the notion that ego-damaging experiences and self-deprecating thoughts cause depression. The mind, however, does not exist without the brain. A considerable amount of evidence though, indicates that regardless of the initial triggers, the final common pathways to depression involve biochemical changes in the brain. It is these changes that are giving rise to the characteristics of depression. (5).

In conclusion, it seems as though depression is caused by a variety of different factors, all of which ultimately induce the same biochemical pathways to produce the effects and onset of depression. There doesn't seem to be one main absolute cause. However, it does seem that all the causes seem to be in accordance with the fact that brain does equal behavior, in that they all seem to induce certain brain activity and the onset of similar biochemical pathways that cause changes in the brain, causing depression. Depression is most likely onset by a combination of the causes mentioned previously and may vary from individual from individual. It is almost analogous with something like heart disease, although one may be predisposed to it, it doesn't mean you will necessarily get it and others may not predisposed to it, but experience it solely because of environmental factors. Similar observations can be observed with depressive episodes, by the fact that there are individuals that exist , that encounter depressive episodes with no history of stress or trauma, thus making the imbalance of neurochemicals or abnormalities in hormone production questionable, yet still display similar brain circuit patterns as depressed individuals. (5). Genetic factors may play a role in this case. However, it can also be argued that genetics isn't the sole cause, perhaps certain people may be predisposed to experiencing depressive episodes but one can't assume by the sole fact that depression runs in families that there is a strong genetic basis, as depressed parents may induce the onset of depression in their kids. Then there are examples that because the emotional needs of an individual are not being met based on ones environmental influences, depression occurs. An example supporting this is observed by the contrast of traditional communities. They tend to naturally meet many basic needs for emotional support. In the traditional Amish society in the US major depression is almost unknown, as it is in the equally traditional Kaluli tribe of New Guinea. In these societies individual concerns are group concerns and vise-versa. (1). Thus, depression can be caused by a combination of factors, such as a combination of individual being pre-disposed to depression and experiencing unfortunate life events simultaneously, or it may be primarily be caused by one or two factors. Lastly, one of the most significant things that most people may miss in the argument of what causes depression is the fact that there is substantial evidence that environmental factors are indeed affecting the chemical pathways of our brain, thus altering one's behavior. (5). So, essentially it may be possible to say that there are two generalized major causes of depression, genetic influences and environmental factors, which cause neurochemical or biological changes producing the symptoms of depression.

References:
1) Depression Learning Path
2) Bush Taking Anti Depressants to control mood swings, amusing article although not sure how legit all of it is.
3) The Neurobiology of Depression
4) Depression
5) Depression Center


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