The relationship between personality and depression is complicated. Certain personality traits could cause someone to be more at risk of depression, be a consequence of being depressed or be a psychological 'scar' from a previous episode of depression. Neuroticism - a proneness to anxiety, emotional instability and self-consciousness - and introversion have both been linked to depression but it is still unclear how much they are causes, and how much symptoms of it. Researchers in Finland compared 193 people with major depression to 388 people from the general population. They compared the participants' scores for neuroticism and depression at the start of the study and again after six and 18 months. They found that among the depressed participants neuroticism and introversion decreased as they recovered from their depression. Those people suffering from depression were more neurotic and introverted than the rest of the participants. The study also found that depressive episodes were unlikely to result in a personality 'scar' over the medium term.
Jylha, Pekka ... [et al] - Neuroticism, introversion, and major depressive disorder - traits, states or scars? Depression and Anxiety April 2009, 26(4), 325-334