Chemical Imbalance/Faulty Brain Wiring Electro-chemical disruption to monoamine neurotransmitters (serotonin, dopamine, norepinephrine, neuropeptides) or neural communication receptors of the limbic system, a part of the brain associated with the regulation of sleep, appetite, memory and emotional processes; low levels, particularly of norepinephrine and serotonin, appear to result in depression, whereas excess or imbalanced levels, particularly of dopamine, appear associated with mania. Neuro -imagery shows lower activity levels in the frontal lobes during depression, the part of the brain associated with higher cognitive processes, and high levels of activity in the amygdala, the part of the brain associated with fear, a possible correlation. Research suggests that with each subsequent period of mood disturbance 1) the period of time between each episode decreases, 2) the episodes occur more readily, and that 3) the experience is more debilitating. 3. Brain Atrophy CT and MRI scans have found atrophy or deterioration in the cerebral cortex and cerebellum in severe cases of unipolar depression and bipolar depression. Patients with left frontal stroke often manifest depressive symptomatology, whereas, patients with right frontal stroke often manifest manic symptomatology. Loss of brain volume (atrophy) in the frontal lobe, prefrontal cortex, and hippocampus, areas associated with emotions and important in the consolidation of information from short-term memory to long-term memory, has been implicated in the development of depression through suppression of the the BDNF (brain-derived neurotrophic factor) protein essential to neurogenesis and cell survival. BDNF modification of synaptic transmission, especially in the hippocampus and neo-cortex, may contribute to conditions such as epilepsy, chronic pain sensitization, and all mood related neuropsychiatric disorders. 4. Hormonal Imbalances Chronic activation (endocrinal default) in the hypothalamic-pituitary-adrenal (HPA) axis, the region that manages the body’s response to stress, has been associated with depression. When stressed, the hypothalamus produces corticotropin -releasing factor (CRF) and other substances that stimulate the pituitary gland to release stress hormones that send a flight-or-fight response. PET scans have also shown decreased metabolic activity in the frontal area of the cortex of people with severe depression. 5. Genetics Genetics are believed to predispose individuals toward or away (vulnerabilities/resiliencies) the development of depression or other mood disorders. Twin studies suggest 46 percent matching for identical twins, compared with 20 percent of fraternal twins. Brain Inflammation Activation or inflammation of Microglia, endogenous immune cells of the brain, by pathogens such as peripheral immune cells or toxins, leeched through the blood vessel walls, has been implicated in depression. Major stimulators of inflammation in our diet are gluten and sugar; depression is found in as many as 52 percent of gluten-sensitive individuals. Disease Model of Depression (neurobiology)