Main assumptions of the biological approach to abnormality
Psychological disorders are illnesses or diseases affecting the nervous system
Understanding abnormal behaviour as a physical illness removes all psychological blame and responsibility for the behaviour from the patient. It isn't their fault and they cannot help the way they behave.Abnormal thinking, behaviour or emotions are caused by biological dysfunctions
Biological dysfunctions, such as changes in neurotransmitter levels, increased levels of certain hormones, or the dysfunction of certain neurones in the brain, can cause abnormal thinking, behaviour and emotions. Understanding mental illness involves understanding what has gone wrong with the brain
Mental illness can be understood and therefore treated by understanding how the brain functions normally, and how abnormal brain function can cause abnormal behaviour. Treatments include drugs that correct abnormal biological functioning and surgery that fixes or removes dysfunctional components of the brain.Possible causes of abnormal behaviour
Abnormal functioning of the brain can be caused by abnormal levels of neurotransmitters and hormones.
Neurotransmitters are the chemical messengers that allow neurones to communicate with one another at synapses (the gap between the end terminal of one neurone and the membrane of the dendrites or cell body of the next). Neurotransmitters that have been implicated in abnormal functioning include:
- Serotinin. Low levels of serotonin are linked to depression, anxiety and obsessive compulsive disorder.
- Dopamine. Parkinson's disease is caused by the death of dopamine producing cells in the substantia nigra. Addiction is linked to the reward pathways that use dopamine as a neurotransmitter.
Hormones are chemical messengers that are secreted into the bloodstream by glands and control various body functions including some nervous system functions. Hormones implicated in abnormal functioning include:
Structural damage or abnormality
- Cortisol. Chronic stress involves high levels of cortisol being produced by the adrenal cortex.
- Insulin. Diabetes mellitus is caused by the inability of cells in the pancreas to produce insulin.
Damage to certain areas of the brain, for example as the result of a head injury, stroke or brain surgery, or a failure of brain areas to develop properly can lead to abnormal behaviour:
Factors that may affect nervous system functioning
- Damage to the hippocampus, as seen in the cases of HM and Clive Wearing, can lead to profound memory loss.
- Damage to Broca's area of the left temporal lobe may lead to the inability to understand speech properly.
- Patients with schizophrenia have abnormally large ventricles in their brains.
Genes are inherited from parents. Many psychological disorders occur more frequently in identical (monozygotic or MZ) twins than they do in non-identical (dizygotic or DZ) twins, and other disorders appear to run in families. Disorders that may be inherited include schizophrenia, autism, addiction and depression. Of course, the environment may also lead to these disorders and so it is important to estimate the degree to which a disorder is due to genetic influences (nature) and the degree to which it is caused by the environment (nurture). Comparing identical twins with non-identical twins for rates of heritability can help answer the nature-nurture question.Infection
Infections, such as meningitis or herpes simplex encephalomyelitis, can lead to abnormal brain functioning.Toxicity
Environmental poisons or toxins may lead to abnormal behaviour. One cause of transgenderism in males may be high levels of prenatal exposure to dioxins in pesticides. Mercury poisoning can cause abnormal behaviour such as the 'madness' that used to be seen in felt makers (immortalised in Lewis Carol's Allice in Wonderland's Mad Hatter).