Depression affects the mind, but this doesn't mean "it's all in your head." Depression is a medical illness linked to changes in the biochemistry of the brain.

• But depression is highly treatable in the vast majority of cases. Up to 90% of depressed people respond positively to treatment. Sometimes psychotherapy or counseling is all that is needed, but there is also a wide array of effective antidepressant medications and alternatives available.

Clinical depression is an umbrella term used to describe the most common forms of depression, which include:

• Major depression, also known as melancholia or unipolar depression, can last up to a year if not treated. A person experiencing an episode of major depression will experience some physical problems, such as headaches or digestive upset, in addition to emotional difficulties.
• Bipolar disorder, once called manic depression, causes mood swings that soar to unusual elation, and then plummet to depression. A person with severe bipolar disorder may also see or hear things that are not there and experience paranoia (a feeling that they are in danger).
• Dysthymia is a chronic (ongoing), low-grade depression. It often begins in childhood or adolescence and may last for many years in adulthood if not treated. It is a less severe form of clinical depression, but at times it can be almost as disabling as major depression.
• Seasonal affective disorder (SAD) is a form of depression thought to be triggered by a decrease in exposure to sunlight. In the Northern Hemisphere, the condition usually occurs in late fall and winter, when daylight hours are short, and it is more common in geographical areas that have four clearly defined seasons.

Perhaps nowhere is the connection between mind, body, wellness, and illness more striking than in depression. It is now believed that human emotions, including sadness, elation, and anxiousness, are governed to some extent by chemical reactions in the brain. That is only the beginning. Scientists have only recently begun to unravel the complex interplay between factors that contribute to depression. Illness, heredity, psychological traits, and social environment are all believed to play a role.

WHAT CAUSES DEPRESSION

The precise cause of depression is not known, but evidence points to several factors, including:

• Heredity
• Biochemical Makeup
• Psychologial Makeup
• Streeful Life Events
• Fluctuating Hormone Levels
• Other Factors such as general medical conditions and certain medications 

Heredity:

Depression does "run in families." People with a close relative who has had major depression or bipolar disorder are twice as likely to develop depression themselves.

Biochemical Makeup:

Every human being has a unique biochemical makeup. Whether or not a person will experience depression (or other neurological disorders) depends largely on the amount of certain brain chemicals and how they interact in the central nervous system (CNS).

A person's biochemistry is an intricate balancing act. Think of a choreographed ballet with a troupe of dancers performing at once. If one or more of the dancers are out of step, the whole production is thrown off balance. So it is with an individual's biochemistry.

The brain is the "master" control center that governs our lives in every conceivable way. Just as messages from the brain (in the form of electrical impulses) control our movements, other messages control our emotions.

Neurons, or nerve cells, are the most basic units in the brain. Neurons are separated by gaps called synapses.

Chemical substances called neurotransmitters carry messages or signals across these gaps to various nerve cells.

If there is a deficiency or an imbalance in certain neurotransmitters, a variety of disorders can result.

The neurotransmitters serotonin, dopamine, and norepinephrine are the chemical messengers believed to be responsible for moods and emotions. Serotonin, in particular, has been implicated in depression. It is believed that a deficiency in the brain of the chemical messenger serotonin - or a disruption in the way it is able to perform its actions as a chemical messenger - has a profound negative effect on mood and emotions.

Psychological Makeup:

In every way, depression is a growing problem. Rates of depression have steadily climbed over the last 50 years and are significantly higher in those born after 1945 than in those born before. In addition, the average age of onset of a first depressive episode is steadily decreasing--it is now mid-20s whereas it once was mid-30s. Cross-cultural data show that the United States has a higher rate of depression than almost any other country, and that as Asian countries Westernize their rates of depression increase correspondingly.

The data make it abundantly clear that these changes are not the product of individual biochemistry or of family genetics but of pathology within our culture. There are many depressogenic factors operating in our culture. Information overload is one. Since 1945 we have accumulated at least as much information as we had throughout history until then. The more information there is, the more we end up essentially skimming the surface. This leads to a style of thinking in which we see only the big picture and miss the depth of detail. As a result, when we are faced with difficult problems, we do not recognize the many small steps that solutions typically require; things feel overwhelming and insurmountable, leading us to give up before we even start.

Our growing reliance on technology also contributes to depression. One of technology's main values is speed. But speed has warped our perspective of time so that we expect things to happen at ever-faster rates. Embracing speed as a cultural value has advantages when you're dealing with things that can actually be done quickly, such as electronic mail, but it is a profound disadvantage when applied to other domains of life, like building a relationship. You can't instantly learn to be a good judge of other people's character or instantly build good relationships with your colleagues at your new job. But people want a good relationship, and they want it now, without having a clue what the steps are and how long it takes to achieve each one. They expect instant intimacy and fool themselves into thinking they've achieved it by sleeping with somebody before they know who the person is.

Depending on whose data you believe, Americans watch between four and seven hours of television per day. This has insidious effects on our culture, such as reducing our tolerance for frustration. Watching major problems occur and get resolved in 30 minutes, with two commercial breaks really does lead us to underestimate the complexity of things. We're willing to vote for Presidential candidates on the basis of eight-second sound bites. No wonder people got enormously frustrated when the Gulf War went into a second day.

It has became fashionable to call depression a disease, to medicalize it. And certainly neurotransmitters like serotonin and norepinephrine are involved in depression. But if you ask the more critical question--is biology the cause of depression?--the best data suggest that genes account for about one in five cases. The idea that a chemical imbalance causes depression, rather than reflects it, ignores the fact that the brain's biochemistry responds to our ways of thinking--in short, to life experience.

When therapists go looking for the cause of depression, they are wasting valuable time. Depression, scientists have learned, is an organized, patterned way of responding to events and experiences. For example, some people develop the tendency to take things personally, even when things are not personal. Or they tend to engage in ail-or-nothing thinking. Either way, the result is that they draw wrong conclusions about events and make the mistake of believing those conclusions rather than testing them. A person whose relationship has broken up tells himself, "No person will ever love me, I'll never fall in love again." And he doesn't, unless somebody comes along and challenges that false belief.

It has long been assumed that when depression runs in families the cause is defective genes. But parents also transmit their general patterns of perception and thinking to their children. Some children are programmed early in life to make grossly negative interpretations about themselves. They bring home an A-minus grade and their father says, "You're a lazy kid. You're grounded until you get an A." Just like that they learn that they're nothing without the A, that it's all or nothing.

Depression is helped most when we encourage people to be active on their own behalf, to challenge their own thinking, to find out whether the thoughts that hurt them are true or not. That's why psychotherapy outperforms medication in the long run. In studies comparing drug therapy to psychotherapy for depression, after about a month medications are ahead; they provide a reduction of symptoms more quickly and more reliably than therapy does. After a couple of months, antidepressants and psychotherapy are running neck and neck; at 12 weeks, therapy is actually slightly ahead. Clients feel better about themselves when they're taking action on their own behalf and learning the principles that will help insulate them from later episodes of depression. As a result, relapse occurs 50 percent more often among patients receiving medication alone than among those receiving both drugs and therapy.

Cognitive therapy, behavioral therapy, interpersonal therapy, and medication all work. But, no matter what, you do need a variety of skills in order to avoid depression. Here are some of them:

Perhaps the most important skill is the ability to recognize and tolerate ambiguity. In many situations in there is no single correct answer but a variety of possibilities. Life is inherently ambiguous; an experiential Rorschach. It is in response to ambiguity that we're most likely to make the negative interpretations that can lead to depression.

Critical thinking is crucial for overcoming depression. By this I mean the ability to examine the evidence and correctly assess the truth of your beliefs, to discriminate between things that you're responsible for and things that you're not. People tend to underestimate or overestimate the amount of control they actually have over situations. If they assume they're helpless when they're not, they don't even try. The ability to recognize what you are and are not responsible for is directly related to how much guilt you experience.

You need to discriminate between ways in which you are defined by your achievements and ways that you are not. Times when it's okay to get in touch with your feelings, and those when you'd better get out of touch with them. When it's okay to focus on the present, and when it's better to concentrate on the future.

Another crucial skill is the ability to clearly articulate goals. Wanting to be happy is not an unreasonable goal. But what exactly do you mean by happy? Whatever else therapists do, they must create learnable sequences for people to follow in achieving their goals. When someone tells me, "I want to be happy." I respond, "Great, let's create a flowchart for how to do that."

A highly important skill for warding off depression is learning to discriminate between what you feel versus what is objectively true. Good mental health requires you to juggle the interplay between what's going on within you and what is going on out there.

Finally, relationship skills are important for preventing depression. We've known for decades that relationships serve as buffers against illness and emotional disorders. The people who are at the greatest risk for depression are those who are most lonely. Demographically, single women face the highest risk; married men, the lowest. So it's crucial to know how to meet people, assess them, communicate with them, let them know you're interested in them. And once you're in a relationship, you need to take steps to keep it healthy, such as asserting personal boundaries and setting up the rules by which the relationship will operate.