Biochemical changesan integral part of depressionmay be triggered by various factors. Whatever the cause, these changes disturb the transfer of information between nerve cells in the brain and the body's ability to manage stress as well as overall mood. Although individual responses vary, researchers suspect that biochemical changes ultimately give rise to the overwhelming sadness and other characteristic feelings suffered by most people with depression.
Mood disorders are believed to originate in specific structures in the brain, primarily an area known as the limbic systemthe brain's emotional center. Among other responsibilities, this region (which includes the hippocampus, the basal ganglia, and the pre-frontal cortex, helps to regulate a person's sense of well-being, appetite, aggression, and sex drive.
Researchers have also identified the limbic system as the origin of imbalances in neurotransmitterschemical messengers in the brainand hormones. In addition, brain imaging scans reveal a decreased metabolic rate in the caudate nuclei and frontal lobes of depressed patients (this rate returns to normal with recovery). The implication of these findings, however, is not fully understood.