Aetiologies of unipolar depression

Depression is most common mental disorder

Strong evidence that its caused by both psychological and physiological factors

Possible that they work together, and that some factors may create depression in the first place, whereas others maintain it

Research using twins show that there could be a genetic basis for this condition - twin studies use MZ twins sharing 100% of genes and DZ twins sharing 50%

Greater similarities between MZ wins than DZ - role of genes has been substantial 

McGuffin et al (1996) studied 177 probands with depression and their same sex twin - found concordance rate for MZ twins was 46% but just 20% for DZ - suggests depression has genetic component but must also be influenced by other things

When compared to other disorders, concordance rates for depression are relatively low - explained by comorbidity - when two or more mental illnesses occur together and prehaps have a common cause

People may inherit a vulnerability to many disorders rather than just depression and so we'd expect to see a higher concordance when looking at range of disorders in related people 

Kendler et al (1992) supported this, finding a higher incidence of mental disorders in twins when looking at depression and generalised this to anxiety as a whole 

Genetic factors thought to act as diatheses in a diathesis-stress relationship 

Genetic predisposition for depression needs to interact with environmental stressors to produce a depressive reaction

Kendler et al (1995) - women who were the co-twin of depressed sibling were more likely to become depressed than those without the vulnerability

Also found that the highest level of depression was found in group exposed to significant negative life events as well as being most genetically at risk - suggest both play a role 

If research correct and depression has genetic basis then researchers should be able to locate responsible genes 

One gene thoought to contribute is the one which is responsible for producing serotonin in brain

This gene comes in three forms, varying in the length of its two stands - believed the form with two short strands leads to insufficient serotonin levels causing depression

Kendler's work supported by Willhelm at al (2006) - negative life events were linked to depression but most importantly, those individuals who had short-short version of the serotonin gene were most vulnerable 

However, vulnerability created by gene was only made apparent when also experienced negative life events suggesting depression is caused by combination of both 

Second physiological explanation is that depression is caused by neurotransmitter dysfunction

1960s - proposed that depression comes from deficient of neurotransmitter noradrenaline 

Bunney and Davis (1965) - indirect markers of noradrenaline such as the by-products found in urine were often low in depressed inviduals - suggesting there wasn't as much noradrenaline 

Role of noradrenaline supported by the fact drugs which cause noradrenaline depletion induce depressive states 

Kraft et al (2005) treated patients with a noradrenaline reuptake inhibitor and they showed a significantly more positive response than those treated with placebo 

Supporting link between low synaptic setononin levels and depression

Cerebrospinal fluid in depression contraining reduced amount of serotonin by-products suggesting reduced levels in the brain itself

Introducing of prozac and other antidepressant drugs that block serotonin reuptake confirmed the association between serotonin and depression

Delgado et al (1990) gave depressied patients who were recieving antidepressant medication a special diet which reduced their levels of the precursors of serotonin - majority of patients experienced a return of depressive symptoms which disappeared again when diet returned to near normal

Some studies use patients whose depression is in remission - Ruhe et al (2007) gave them an amino acid mixture to eat that temporarily reduces levels of serotonin in the brain and they tended to experience brief relapse of symptoms - suggests low serotonin causes depression

Freud (1917) propsed that some cases of depression could be explained by genetic factors, but many cases were linked to childhood eperiences of loss or rejection which had been repressed

Individuals harbour negatvie feelings towards those they love - later in life, if someone is lost the repressed feelings resurgace but are turned inwards

Frued emphasised role of anger in mourning and depression and to him, depression was "anger turned against onself"

Studies found many people who suffer with illness describe their parents as "affectionless" supporting Frued's theory of "loss" through withdrawral of affection causing depression

Bifulco et al (1992) found evidence that children whose mothers die in early childhood were more likely to become depressed in later life - also found association could be explained by lack of care from parents and parent substitutes following loww, rather than loss itself 

Paykel and Cooper also suggested early loss accounts for only small amount of depression with just 10% of those who experience loss becoming depressed, suggesting other causes for depression

Beck (1967) believed that depressed individuals think as they do because they are biased towards negative interpretations of the world and have a negative schema

Could be caused by many favtors and activated whenever individual encounters a new situation that resembles original conditions in which the schema were learned 

Negative schema maintain what Beck calls the negative triad - pessimistic view of self, world and future which causes depression 

Beck's research supported by Hammen and Krantz (1976) who found depressed women make more errors in logic when asked to interpret written material than non-depressed - show fault in thinking  

However, as with many epxplanations, the fact that there is alink between negative thoughts and depression doesnt mean former causes latter

Seligman (1975) proposed depression may be learned when person tries but fails to control an unpleasant circumstance so develops sense of being unable to control their life - Learned helplessness impairs their performance in situations that could be controlled

Person prone to depression is thought to show a depressive attributional style - accepting they cant change how their life goes and accepting their depressive state

Although Seligman's initial research was based on study of animals, learned helplessness has been supported by human studies 

Miller and Seligman (1974) found that depressed students exposed to an uncontrollable event performed worst of all on similar cognitive tasks - findings sugges tthat having some depree of control is likely to improve performance expecially for those depressed