Clinical depression is very common. More than nine million Americans are diagnosed with clinical depression at some point in their lives. More and more people are suffering from clinical depression because they are not seeking treatment. They may think depression is a personal weakness or try to cope with their symptoms alone. On the other hand, some people are easy to admit their symptoms and seek help. Such a gap may explain differences in reported cases of depression between men and women, which indicate that more than twice as many women as men are clinically depressed. Based on the number of reported cases of depression, 25% of women and 10% of men will experience one or more episodes of clinical depression during their lifetime. The biological basis of clinical depression originates in the brain. Your brain is made up of a complex network of nerve cells, called neurons, and brain chemicals, called neurotransmitters. Neurotransmitters transmit messages from one neuron to another. Two of these neurotransmitters are not produced in sufficient quantities in the brain of a depressed person. Due to this lack, too few messages are transmitted between neurons and symptoms of depression appear. In clinical depression, chemicals in the brain are out of balance. New technology allows researchers to take photos of the brain that show brain activity levels. These imaging techniques like fMRI and PET actually create images of how active different parts of the brain are. Some studies using these types of techniques have suggested that the activation patterns in the brains of depressed people are different from those of others. These tests can help doctors and researchers learn more about depression and other mental illnesses. Because this research is relatively new, it is not yet used to diagnose clinical depression. Strong evidence suggests that clinical depression is hereditary. Yet just because a person has family members with clinical depression does not mean they will develop it. Likewise, you can have it even if no other member of your family has had it. People with high levels of stress are much more likely to develop depression than those who do not. Although most people go through a period of "depression" after a particularly stressful event such as a divorce or the death of a loved one, sometimes extremely difficult stresses can trigger depressive episodes in some people susceptible to the illness...