How the Brain Triggers Depression
Alterations of chemicals in the brain are responsible for triggering depression. Researchers have worked hard to understand the complexity associated with hormones and neurotransmitters in the brain and how depression is triggered, made worse, and why in some individuals depression recurs or becomes chronic and severe. Stressful physical and emotional vents seem to trigger depression. Why some individuals respond to those events by experiencing depression has been the target of research and the focus of drug development and therapy for centuries.
Brain Chemicals
Scientists do not know what happens first in the brain to trigger depression. It may be that signals in the brain from neurotransmitters become impaired in response to stress and trauma, leading to depression. On the other hand, changing behavior can change signals in brain and alleviate depression. Either way, the most widely held belief by scientists is that alterations in neurotransmitters (chemicals that send electrical signals), serotonin, norepinephrine are the root cause of depression.
Hormones
Individuals with depression often have abnormal hormone levels. Again, scientists are not certain whether depression acts to alter hormone levels, or whether abnormalities in hormone levels cause depression. The stress hormone cortisol is elevated in half of individuals with depression. Cortisol levels decrease when depression is treated. Abnormal levels of thyroid hormone might also trigger depression.
Newer Research
Genes are thought to play a role in depression. Research conducted by scientists at Northwestern University suggests that neither imbalance of neurotransmitters in the brain or stress trigger depression. A study, conducted on four different genetically strains of rats, found no link between stress and depression genes. Depression researcher Eva Redei identified specific genes in depressed rats that are related to depression, located in the brain--specifically the hippocampus and amygdala, after exposing rats to stress for two weeks. Redei was unable to find any overlap between depression and stress genes. Redei says the notion that altered levels of neurotransmitters in the brain trigger depression is wrong. The purpose of the study was to find more effective drugs to treat depression. Studying rodents to find out whether stress is a trigger for depression is applicable to humans because of similarities in brain structure.
Events Known to Trigger Depression
Despite debate about what chemicals trigger depression in the brain, certain events are known to contribute to or induce depression. In addition to physical and emotional stress, seasonal affective disorder (SAD), insomnia, physical illness, such as multiple sclerosis, Parkinson's disease and dementia, and pain have been identified as triggers for depression.
