... This leads researchers to believe that depression, which can be brought about by either genetic or environmental factors, is (at the biological level) a change in the chemical activity at the neuron's synapses [Miell, Phoenix and Thomas, 2002, p276]. Without an understanding of the nervous system and synaptic function this kind of treatment would not be possible and previously sufferers of this disease would have gone untreated. Depression is a good example of a mental illness that has been found to have an inherited susceptibility factor, but this is not exclusive or determinant [Anisman and Zacharko, 1982, citied in Miell, Phoenix and Thomas, 2002, p276]. If the 'prone to depression' gene is passed on, depression will not necessarily ever surface. Sometimes it will surface from no environmental factor whatsoever, and sometimes a trigger factor will start it. It is also possible in certain external circumstances to have depression without ...

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