Causal Models Of Mental Disorders

Causal Models of Mental Disorders

Biological Accounts

Genetics

Hereditary

Mental illness tends to run in families. Fig 1. shows a heritability link with schizophrenia. (Bienvenu et al, 2011).

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Gene Associations with Mental Disorders

There are multiple links between various syndromes that involve missing a gene, and a mental disorder.

E.g. VCFS is a syndrome that involves missing the COMT gene (involved in breaking down dopamine). It has a 25% schizophrenia rate.

E.g. Fragile X syndrome is caused by a mutation on the FMRI gene (x-chromosome). It has a 15-60% autism rate, and accounts for ~5% of autism diagnoses.

Neurophysiology/Brain Abnormalities

Unusual brain structure and function have both been linked to mental disorders;

  • OCD commonly has regions of abnormal white matter integrity. (Structure).
  • Depression has unusual regions of brain hyperactivity. (Function).

Limitations of the biological account

Even the most highly heritable mental illnesses are a long way off being entirely heritable. Fig 1. above shows that even for identical twins there's <50% risk of both developing schizophrenia.

And whilst links have been found between genes and mental disorders, there are no individual causal genes, just influencing ones. Biomarkers seem to be improving, and there's been recent work done into schizophrenia ones, but overall there's nothing dramatic.

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Environmental Accounts

Environment can override genetically influenced tendencies for behaviour, and early psychological experiences can modulate the effect of neurobiology.

Examples

Insel et al (1988) used 2 groups of monkeys given benzodizapine inverse agonists to demonstrate the effect of environment.
Group 1 had access to food and toys under their own control; Group 2 had access whenever group 1 did (no control).
Group 1 reacted with aggression, and group 2 with anxiety/panic.

Francis et al (1999) took rat pups from an un-nurturing mother and placed them with either a nurturing or un-nurturing mother, and found the nurturing group were more nurturing as adults.

Biological+Environmental (Nature AND Nurture)

The Diathesis-Stress Model explains psychological disorders as result of genetic vulnerabilities and life stressors.

The theory is that individuals inherit genetic vulnerabilities towards mental disorders that may become activated under environmental stressors. With a higher vulnerability, less stressors would be needed to trigger it.

One example is Capis et al's 2003 study of 5HTT alleles, finding that different combinations of alleles and stressors affected probability of depression.

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Psychological Accounts

Psychoanalytic

Psychoanalytic (or better known as Freudian) methods consider the cause of psychological disorders to be overuse of defence mechanisms that allow the ego to discharge the Id's energy without allowing unconscious impulses into consciousness.

Examples

(See main article on psychoanalysis).

  • Projection
    • Projecting unconscious impulses onto other people.
  • Reaction
    • Transforming unconscious impulses into compulsions.

Behavioural

The behavioural model is a reaction against psychoanalysis; believes everything is nurture, and everything is conditioning (rather than suppressed impulses, it's learned responses).

Each variant of behaviourism (the classical, operant and vicarious conditioning flavours) focusses on maladaptive behaviour, either as a learned response, a reinforcement of it or picked up from bad role models.

Cognitive

Cognitive theories argue that there is no direct relationship between consequences and events, but rather a strong influence based on how we interpret events ("As I think, so I Feel").

Beck's ABC Model

Aaron Beck is regarded as the father of cognitive therapy. His ABC Model goes A->B->C, rather than A->C:

  • A = Activating Event
  • B = Beliefs
  • C = Emotional Consequences

Account of Mental Disorder

Cognitive accounts of mental disorder consider them to be caused by distortions in thinking, or a maladaptive cognitive style.

Biological and Psychological Accounts

There's definitely a link between psychological and biological accounts of mental disorders; both psychotherapy and pharmacotherapy are effective, and both work by changing brain function.

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The brain and mind are linked in ways we don't yet understand, but are definitely complex.