Biological explanations of depression PSYCHOPATHOLOGY Biological explanations of depression

Genetic factors

Concordance rates 46% MZ twins 20% DZ twins (McGuffin et al. 1996)

Diathesis-stress model Genetic predisposition Environmental triggers Kendler et al. (1995) – Virginia twin study Women genetically predisposed (twin has the disorder) more likely to develop depression if they have negative life events than women who were not genetically predisposed.

Biochemical factors Neurotransmitter activity Chemical messengers in the nervous system Associated with reward and punishment Help to regulate the hypothalamus Involved in sleep, appetite, sexuality and physical movement Key areas affected in depression

Noradrenaline (Norepinephrine) Low levels of Noradrenaline implicated in depression Support for this idea comes from the use of drugs which affect Noradrenaline levels Reserpine is a drug given for high blood pressure. Reserpine depletes levels of Noradrenaline Depression is an unwanted side-effect of Reserpine.

Further support Antidepressant drugs such as tricyclics and Monamine Oxidase Inhibitors increase amounts of Noradrenaline and Serotonin in the synapses. They have been found to be effective in relieving the symptoms of depression.

However Selective Serotonin Reuptake Inhibitors (SSRIs) such as Prozac have negligible effects on Noradrenaline. SSRIs are effective. This suggests that serotonin has a role in depression rather than Noradrenaline.

Complex picture It is not a simple situation. Neurotransmitters have a complex relationship with each other and links with different aspects of human behaviour, e.g. Noradrenaline – energy, serotonin – rumination on grief, despair and guilt, Dopamine - pleasure

Further complexities Drug treatments have effects on the brain other than just on neurotransmitters. It is not certain that it is the change in neurotransmitter levels that brings about the effectiveness of the drug.

Another problem Drugs alter neurotransmitter levels immediately. However, mood symptoms are not relieved for several weeks. This is another indication of the difficulty of trying to attribute depression to neurotransmitters.

Cause or effect? The change in levels of neurotransmitters could be a result of depression rather than a cause of it.

Neuroendocrine factors Cortisol is a stress hormone. The hypothalamus regulates cortisol levels. When Noradrenaline levels are low the hypothalamus loses this ability. High levels of cortisol are often found in depressed people. However, high levels of cortisol are not specific to depression (they are also found in people with anxiety disorders). It is not clear whether raised levels of cortisol are an effect or a cause of depression.

Neuroanatomy The frontal cortex Especially the anterior cingulate Comes up with sad abstract thoughts And gets the limbic system involved.

Summary The biological approach to explaining depression suggests that it is a disease in the same way that diabetes is a disease. However, this is a reductionist approach. It is too simplistic to ignore psychological factors.