Depression

While diagnosing depression can prove tricky, depression does have clear biochemical roots that affect nerve cells in the brain. Severely depressed people have unusually low levels of several brain chemicals: the neurotransmitters serotonin, dopamine, and norepinephrine. Neurotransmitters carry messages from one nerve cell to another. The unusual levels of these chemicals may be inherited, which may explain why depression tends to run in families. Although researchers have yet to discover a depression gene, many suspect a genetic connection.

Deep emotional losses can also trigger the biochemical changes that cause depression. Profound trauma in early childhood—the death of a loved one, a bitter divorce, physical or sexual abuse, or other very disturbing experiences—can cause depression later in life. Just as frequently, though, the brain chemistry of depressed individuals changes for no apparent reason. People who are well adjusted and well loved can also become seriously depressed.