There are many biological causes of clinical depression. The brain has been studied extensively to understand the chronology of brain function, the influence of neurotransmitters and hormones and other biological processes and also how central they are - to the development of depression.
The brain is a commander-in-chief of the human body. It controls the basic functions of our bodies, our movements, and our thoughts and emotions.
Researchers studying clinical depression tend to look at several aspects of brain function including the structures of the limbic system and the function of neurotransmitters within neurons.
’Limbic System’ is the area of the brain that governs activities such as emotions, physical and sexual drives, and the stress response.It's activities are significantly complex and any irregularity in any part of it, including how neurotransmitters function, could take a toll on an individual's mood and behavior.
'Hypothalamus' is a small structure located at the base of the brain, responsible for body temperature, sleep, appetite, sexual drive, stress reaction, and the regulation of other activities. It also controls the function of the pituitary gland which in turn regulates key hormones.
Neurotransmitters and Neurons: They are special chemicals called neurotransmitters carrying out many very important functions, like: helping transfer messages throughout structures of the brain's nerve cells. These nerve cells, called neurons.
Neurotransmitters have been found to be associated with clinical depression. They function within structures of the brain that regulate emotions, reactions to stress and the physical drives of sleep, appetite, and sexuality.
Theories about how neurotransmitters may be related to a person's mood have been based upon the effects that antidepressant medications can have relieving depression in some people. It is believed that these medications are effective because they regulate the amount of specific neurotransmitters in the brain.
However, whether that neurotransmitters play central role in the development or treatment of clinical depression is ambiguous. For instance, it has been shown that many people who are depressed have low levels of the neurotransmitter norepinephrine. The use of some antidepressants can increase the level of norepinephrine in the brain, and subsequently relieve depressive symptoms. One the other hand, it has also been shown that some other people who are depressed have high levels of norepinephrine. This same scenario may be true for other neurotransmitters.
The reason why the effects of neurotransmitters are not clear-cut has to do with the fact that antidepressant medications do not work in the same pattern for every individual. If there were a direct causal link between the level of a neurotransmitter in the brain and depression, then we would expect a much higher rate of success with medication. Further, although antidepressant medications can change the level of a neurotransmitter in the brain immediately, it normally takes a few weeks for a person with depression to feel better.
The effects of neurotransmitters is very difficult to study as they are present in very small quantities and are only available in certain locations within the brain, and they disappear very quickly once they are used. Because they are removed so fast, they cannot be measure directly. Researchers can only measure what is left over after their use in the brain. The substances that remain are called metabolites and they can be found in blood, urine, and cerebrospinal fluid. By measuring these metabolites, researchers can gain an understanding of the effects of changes in neurotransmitters in the brain.
It is unknown whether changes in levels of neurotransmitters cause the development of depression or depression causes changes in neurotransmitters. It may happen both ways.
Researchers believe that our behavior can alter our brain chemistry and that brain chemistry can affect behavior. For instance, if a person experiences numerous stressors or traumas this may cause his or her brain chemistry to be affected, leading to clinical depression. On the other hand, that same person may learn how to change depressed thoughts and behavior and cope with stressful events. Doing this may also change brain chemistry and relieve depression.
(The content has been summarised, using content from the site below)
http://www.allaboutdepression.com/cau_02.html
Prof Jyotsna Sawhney is a Management Faculty & keeps involved in Researches On Corporate Situations (specially: Indian), article writing, Management training, in her domain areas: Corporate Communication & Marketing.
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