biological explanations

• Genetic basis of schizophrenia

  Schizophrenia is a partially genetic disorder, inherited through hereditary means (through the genes passed on to individuals from their parents) and therefore runs in families.
• What is meant by the term concordance rate?

  The likelihood of one twin having the disorder if the other twin has it.

  Identical (MZ) twins share 100% of DNA

  Fraternal (DZ) twins share 50% of DNA

  MZ twins have a higher concordance rate
• Gottesman (1991)


  Schizophrenia runs in families. Probability of schizophrenia = 48% between MZ twins, 46% if both parents had it and 10% between DZ twins. Strong evidence that schizophrenia is genetic
• Candidate gene

  A gene that has been identified to be responsible for Schizophrenia. It is not believed that there is a single “schizophrenic gene”
• Polygenic gene

  Several genes may be responsible for schizophrenia
• Schizophrenia genetics

  Schizophrenia is polygenic(involves a combination of genes) and is aetiologically heterogenous(a number of different combinations of genes can lead to the illness)
• Ripke et al (2014)


  Compared the entire genetic makeup of 37,000 patients compare to 113,000 healthy controls and found 108 separate genetic variations associated with increased risk of the disorder.
• Tienari et al (2004)


  Children adopted from 19,000 Finnish mothers at birth were compared with a control group (no genetic risk). It was found that harsh parenting was associated with schizophrenia in the children but ONLY for those who had a genetic vulnerability. Biological children of parents with Sz are at a greater risk even if they grow up in an adoptive family. Genetics make people more vulnerable!
• What are neural correlates?

  Abnormalities in structure or function of the brain that correlate with positive or negative symptoms of schizophrenia.

  - Ventricular enlargement

  - Dopamine hypothesis
• Enlarged ventricles

  80% of Schizophrenics have enlarged ventricles (fluid-filled spaces between brain areas) = a loss of brain tissue. Enlarged ventricles is associated with damage to central brain regions and pre-frontal cortex. Often associated with the negative symptoms of schizophrenia

  
• What are neurotransmitters?

  Neurotransmitters are fast chemical messengers that travel between neurons (brain cells) by crossing the synapse. They bind themselves to receptors on the next neuron and pass on their message in the form of a small electric charge. Dopamine is an important neurotransmitter that regulate mood and attention.
• Who first proposed the dopamine hypothesis?

  Arvid Carlsson
• What is the dopamine hypothesis?

  The idea that schizophrenia involves an excess (hyper) / lack (hypo) of dopamine activity. Dopamine is an excitatory neurotransmitter.
• Hyperdopaminergia in the sub-cortex

  Abnormally high levels of dopamine in the sub-cortex (inner parts of the brain) causing an over activation of neurons, resulting in positive symptoms of schizophrenia e.g. in Broca’s area (responsible for speech production) associated with auditory hallucinations and speech poverty

  
• Hypodopaminergia in the cortex


  Abnormally low levels of dopamine in the pre-cortex (responsible for decision making) causing an under activation of neurons. Goldman-Rakic et al(2004) Hypodopaminergia in the pre-frontal cortex could explain negative symptoms in Sz

  
• Curran et al and Tauscher et al - support of dopamine hypothesis


  Curran: Amphetamines (Dopamine agonists - increase DA) mimic Sz symptoms. Tauscher: Antipsychotic drugs reduce intensity of symptoms because they reduce dopamine.

  These findings suggest that dopamine is involved in the symptoms of Sz
• Mixed evidence - limitations of the dopamine hypothesis

  Noll: Argues that 1/3 of patients do not respond to drugs which block dopamine so other neurotransmitters may be involved. Suggests that there is mixed evidence for the dopamine hypothesis as research has shifted to the role of other neurotransmitters showing they also have a role in Sz
• Chicken and the egg - limitations of dopamine hypothesis

  Now criticism of the dopamine hypothesis is there is a problem with the chicken and the egg. Are raised dopamine levels the cause of the schizophrenia of is it the raised dopamine level the result of Sz. It is unclear which comes first ∴ we need to be careful when establishing cause and effect relationships in schizophrenic patients
• Environmental factors - limitation of biological explanation

  Evidence to suggest an important role for environmental factors. The probability of developing Sz even if your an MZ twin is less than 50%. This challenges genetic explanations as if Sz was caused purely by genetic factors the probability should be 100%
• Demand characteristics in twin, family and adoption studies - limitation of biological explanation

  Twin, family and adoption studies must be considered cautiously because they are retrospective and diagnosis may be biased by knowledge that other family members who may have been diagnosed. This suggests the findings may lack validity due to the possibility of demand characteristic