1. Etiology of Depression - Biology

2. Genetics Genetic factors may predispose people to depression Nurnberger + Gershon (1982) reviewed twin study results found the higher concordance rate between MZ twins than for DZ twins However this only means they are more likely to develop depression compared to people in the same circumstances without genetic predisposition Correlation does equal causation Caspi et al (2003) said that the results indicated that genetic factors moderate responses to environmental factors, and they also warm that speculations about clinical implications of these findings is premature

3. Neurotransmission depression may be caused by a deficiency in neurobiological systems such as neurotransmitters and hormones catecholamine hypothesis (Joseph Schildkraut 1965) suggest depression is associated with low levels of noradrenaline theory was developed into the “serotonin hypothesis”, the idea that serotonin is the neurotransmitter responsible Janowsky et al (1972) results showed that a depressed mood could be artificially induced by certain drugs Delgado + Moreno (2000) found patients with MDD had an imbalance of several neurotransmitters, including noradrenalin, serotonin, dopamine, and acetylcholine

4. Neurotransmission cont. However this could indicate that having depression caused these imbalances not vice versa – Burns (2003) says that he has never seen any convincing evidence that depression results from a deficiency of brain serotonin Lacasse + Leo (2005) argue that contemporary neuroscience has failed to provide evidence that depression is cause by simple neurotransmitter deficiency. According to them, modern neuroscience has instead demonstrated that the brain is very complex and poorly understood

5. Hormones cortisol hypothesis says that stress can predispose an individual to psychological as well as physical disorders cortisol is a major hormone of the stress system possible like between long-term stress and depression indicated by the fact that patients with MDD have high levels of cortisol supported by findings from studies on victims of childe abuse however the relationship between stress and depression is not yet well understood people develop depression without previously being stressed, and people who have experienced terrible stress do not necessarily develop depression