For many decades, a bitter argument has been raging in the psychiatric community between those who feel that the causes of depression are genetic and biological illness and those who feel that they are psychological and social. Fortunately, an increasing number of clinicians are subscribing to the “fertile ground” theory, which says that “depression is a genetic disorder of the mind-body-spirit which occurs when predisposing factors combine with environmental stressors.
In other words, for clinical depression to occur, two factors are usually present:
- Biochemical or physical predisposition (which provides the fertile ground)
- A triggering stressor, which brings on the actual episode. (There are times, however, when an episode can mysteriously begin “out of the blue.”)
Predisposing Factors
A predisposition to clinical depression can be caused by a variety of genetic, biochemical, and environmental factor:
- Family history. Depression, like heart disease, runs in families. If one parent has suffered from depression there is a 25 percent chance that a child will develop the illness; if both parents are depressed, the risk rises to 75 percent.
- Biological imbalances. These include imbalances in the brain’s neurotransmitters as well as hormonal imbalances (such as low thyroid).
- Early childhood trauma. These include abandonment, abuse, neglect, birth trauma, death of a parent, and divorce. Such trauma permanently alters the nervous system as seen by the fact that the best predictor of depression in adulthood is the death of a child’s parent before the age of eleven.
- Our basic temperament. The work of Harvard psychologist Jemome Kagan with infants clearly demonstrates that we are born with a “temperamental bias.” In his research with infants, Kagan has identified two types of children:
- The inhibited, high reactive child: This child is shy, reserved, anxious, cries easily, and tends to withdraw in novel social situations. He or she may become quiet, hold a parent’s hand, or retreat altogether.
- The uninhibited, low reactive child: This child is outgoing, open with strangers, and at ease in new social situations. Rather than cling to the mother or hide, he or she will openly explore the novel environment. This child is described as spontaneous, playful and quick to laugh or smile.
Kagan believes that these babies were simply born with different brain chemistry. *Neuroscientist Richard Davidson has confirmed Kagan’s research by demonstrating in his laboratory that the low reactive children have pronounced activation in a region of the brain called the left prefrontal cortex and less activity in the amygdala (the brain’s fear mechanism). Conversely, Davidson has found that depressed, unhappy people have more activity in the right prefrontal cortex of their brains (not the left), and have especially overactive amygdalas.
Environmental Triggers
Now that we have looked at the genetic/biochemical causes of depression, let’s turn our attention to the environmental ones. Environmental factors include.
- Loss and separation. Death of a loved one, divorce, marital separation, or any interpersonal conflict are major triggers for depression.
- Financial stresses such as a loss of a job or being in debt.
- Physical illnesses. Any chronic illness such as heart disease, cancer, AIDS, multiple sclerosis, Parkinson’s, etc., can trigger symptoms of depression.
- Infections. For example, streptococcal bacteria—those that cause strep throat—also attack the basal ganglia in the brain, and have been implicated in obsessive-compulsive disorder, anorexia nervosa and Tourette’s syndrome. Other pathogens, such as T Pallidum (the syphilis-causing bacteria) and the human immunodeficiency virus have been known to cause anxiety, delirium, psychoses, and suicidal impulses.
- Adverse reactions to prescription drugs.
- Social isolation. Many studies show identify isolation as a contributing risk factor for depression. For example, a British study showing that single parents were more likely to become depressed than married ones.
- Environmental toxins.
- Moving or changing employment.
- Substance abuse. Drug and alcohol use can clearly elicit the symptoms of depression.
Biology Is Not Destiny
The fertile ground theory tells us that although environmental factors play an important role in mood disorders, people do not suffer from serious episodes of depression and anxiety without a biochemical predisposition. Does this mean that we are doomed by our genes and temperament? Not necessarily, says Jemome Kagan:
For example, if a “high reactive” infant is raised in a good environment by great parents, is good in school, and has lots of friends, then this child will not end up unhappy, but relatively happy. It’s just that he’s got to fight the bias. Remember, if you’re born with a gene that says you’re going to be 6 foot 9, then your biased to be a great basketball player. But there are some short men who are great basketball players. They overcame their bias. And that’s true for everything in life.*
Other neuroscientists concur with Kagan. Joseph Ledoux, the scientists at New York University who has done pioneering work on anxiety and the brain, says,
“The brain has plasticity, the ability to rewire itself in response to environmental stimuli and any kind of learning.”
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