Everyone experiences depression at some time in their lives. On holidays like today, the number of people feeling depressed skyrockets. For most of them, their spirits will return when the holidays are over. For some people, however, depression is a constant factor in their daily existence. It can deprive them of the enjoyment of life and can even lead to suicide. Over the years, I've known several people who were close to me who had this terrible affliction. As a scientist, I've often wondered what causes it and how to cure it. Before it can be cured, however, it's necessary to understand what depression really is.

It's fashionable these days to say depression is a chemical imbalance. Of course, at some level this is true. Chemical imbalances, such as those that occur in seasonal affective disorder, can cause feelings of depression; and drugs that counteract the chemical imbalance can help mitigate the symptoms. But a chemical imbalance of neurotransmitters is no more a cause of real depression than an imbalance of arachidonic acid metabolites is the cause of a headache. Taking aspirin may block the cyclooxygenase enzyme that creates the signaling molecules, but it's not "curing" the headache--only making it impossible to feel it.

And what about other emotions? Anger and happiness may also be described as a chemical imbalance, but this doesn't explain them and it ignores the psychological meaning of the emotion. This deprives us of an understanding of how the chemical imbalance forms in the first place.

Depression is usually characterized as an emotional state, with overpowering feelings of sadness, helplessness, and worthlessness. The victim withdraws from former activities and appears to act passively. But whether the victim realizes it or not, there is nothing passive about depression. Inside the person's mind there are powerful feelings of aggression and hatred. After all, what could be a more convincing expression of violent aggression and vicious hatred than the act of killing oneself?

Indeed, aggression and depression have often been linked in the research literature [refs]. Although it's hard to prove this scientifically, I am convinced that depression is aggression turned inward against oneself. All emotions are the body's way of getting you to do something. Depression is no exception. The affective component of emotions is a powerful clue about what the brain wants you to do. In the case of anger or sexual desire, the course of action is more or less obvious. In the case of depression, the course of action is not so clear. I hypothesize that depression is the brain's way of getting you to do something in your life that is painful.

Before explaining this, it's necessary to explain the relationship of depression to learned helplessness. Some of my colleagues are studying learned helplessness in rats as a model for depression. The animals are placed in a small swimming pool. This doesn't hurt them, because they are natural swimmers. But they'd rather be in their cage where it's dry. For half of the animals, a platform is provided that allows the animal to escape the water. The other half have no escape from the water until the experimenter takes them out. These rats learn that it's pointless to struggle so they stop searching for a way out, and after several sessions they fail to utilize an escape platform even when one is provided. This is called learned helplessness.

One might think that laboratory rats would automatically be depressed. After all, they are in a sterile cage with little personal freedom or privacy. But rats are very practical creatures. Judging from their behavior, rats appear to think they have it pretty good. They have free food, other rats to sleep on, doctors in lab coats waiting on them hand and foot, and they can go for a dip in the pool once a day. It's depressingly tough to get the rats depressed under these conditions.

The remarkable thing about learned helplessness is that drugs that act as antidepressants disrupt learned helplessness. This makes learned helplessness a very useful tool for screening potential new antidepressants.

However, learned helplessness is probably not true depression, in the sense that we humans think of it. The rats aren't depressed. They don't sit around reading No Exit or books by Franz Kafka about people turning into cockroaches, or lie around in their cages wearing black polo shirts and discussing the meaninglessness and futility of their existence. But maybe they should, because just as it prevents them from trying to escape the swimming pool, learned helplessness prevents people from using the coping strategies that are available to most people to escape depression.

A depressed person who stays depressed may do so because their coping strategies don't work, or the person is afraid or unable to make the necessary changes in their environment. As a result, the situation that causes the depression doesn't change and the condition gets worse.

Although this theory is still very primitive, it suggests that antidepressant medication is not sufficient for curing depression. The patient is not depressed without a good reason. To escape, the patient must also make a radical change in his or her life.