biological explanations

• biological explanations


  correlation method to determine if behaviour is due to nature or nurture

  use twin studies to determine a concordance between characteristics

  if one twin develops SZ the chances of the other doing so is high

  the higher the concordance the higher the chance of genetic relatedness of the disorder
• genetic vulnerability 


  proposed that there is a genetic component to SZ which predisposes some individuals to the illness~

  explanation suggests that whether a person develops SZ is partly due to their genes, why patients often have other family members with SZ

  family studies: find individuals who have SZ and determine whether their biological relatives are similarly affected more often than non-biological relatives using correlation
• family studies:

  Gottesman (1991): concluded that if both parents suffer from SZ, there is a 46% chance of also developing the disorder

  shows that genes play an important role however if they were the only factor the percentages would be 100%

  could be deterministic: just because we are 'predisposed' by our genes doesn't mean we necessarily get SZ

  researchers now accept that SZ concordance rates in families may be more to do with common rearing patterns or other environmental factors that have nothing to do with heredity: interactionist approach
• twin studies:

  if MZ twins have a higher concordance than DZ twins, a genetic link?

  researchers worked out if nature or nurture had a bigger influence

  Gottesman and Shields (1972): found that the concordance rate for SZ in the MZ twins was 48% compared to 17% in DZ twins, suggests heredity

  indicate a strong component, demonstrate a predisposition to developing SZ but not always, suggesting an environmental influence

  concordance rate isn't 100% so SZ can't be account for by genetics alone

  sample sizes are always small so difficult to generalise to wider pop
• adoption studies

  these studies allow researchers to overcome problem of disentangling genetic environmental influences

  Heston (1966) compared 47 children whose biological mother had SZ with a control group of children with no history of SZ, none were diagnosed but 16% with biological influence were diagnosed

  suggests a genetic basis to the disorder

  SZ could be a polygenetic disorder (more than one gene causing it)

  nature vs nature debate, accepts an interactionist approach
• the dopamine hypothesis:

  dopamine: a neurotransmitter (NT) that serves as a chemical messenger in the brain, can function as both an excitatory and inhibitory NT, causing diverse effects on the brain, body and behaviour

  function: associated with pleasure, reward, motivation and motor control, linked to feelings of gratification and is implicated in mood disorders, addiction and certain behaviour when levels are imbalanced

  cognitive neuroscience studies are highly scientific: causal explanations
• drugs that increase dopamine activity:

  claims that an excess of the NT dopamine in certain regions of the brain is associated with the positive symptoms of SZ

  SZ's are thought to have abnormally high numbers of D2 receptors on receiving neurons resulting in more dopamine binding and therefore more neurons firing

  evidence: amphetamine is a dopamine agonist, stimulates nerve cells containing dopamine causing the synapse to be flooded with this NT

  normal people exposed to large doses of dopamine releasing drugs can develop characteristic symptoms of a SZ episode, disappear when the drug stops
• drugs that decrease dopamine activity:

  antipsychotic drugs: block the activity of dopamine in the brain, these drugs were found to eliminate symptoms, like hallucinations/delusions

  the fact that these drugs that block dopamine activity alleviated many of the symptoms of SZ strengthened the case for the role of dopamine

  revised dopamine hypothesis:

  Davis and Kahn (1991): positive symptoms of SZ are caused by an excess of dopamine in sub-cortical areas especially the mesolimbic pathway

  the negative symptoms are thought to arise from a deficit in dopamine in the mesocortical pathway
• dopamine hypothesis evidence:

  PET scans show lower levels of dopamine in the dorsolateral prefrontal cortex compared to normal controls

  the dorsolateral prefrontal cortex is where the mesocortical dopamine pathway is therefore support for low dopamine in this pathway leads to deficit of dopamine activity and negative symptoms of SZ

  lots of success of drug treatment to change levels of dopamine activity

  Leutch et al (2013) carried out a meta-analysis of 212 studies that analysed the effectiveness of different antipsychotics with a placebo, all drugs were more effective than the placebo
• evaluation:

  biological determinism: PET scans can establish a cause for SZ symptoms by measuring dopamine in normal and SZ patients but may be limited as other NT may be involved

  explains how both positive and negative symptoms simultaneously as different parts of the brain are affected by dopamine differently led onto the development of more advanced drugs targeting specific sites so biological reductionism is good, more specific treatment

  biological reductionism also led to a loss of a holistic understanding experience of SZ symptoms and led to the simplification of the disorder
• neural correlates

  measurements of the structure or function of the brain that occur in conjunction with an experience, SZ

  evidence shows SZ is caused by structural abnormalities in the brain

  brain scanning techniques have made it possible to investigate living brain images, cognitive neuroscience

  prefrontal cortex: main area of the brain involved in executive function (planning, reasoning and judgement), its impaired in SZ patients

  hypothesised that the cognitive systems of SZ results from deficits within the prefrontal cortex and its connections to other areas of the brain
• prefrontal cortex:

  several studies have reported anatomical changes in the hippocampus of SZ patients

  deficits in the nerve connections between the hippocampus and the PFC have been found to correlate with the degree of working memory impairments

  white matter: found in the brain and spinal cord and made up of nerve fibres covered in myelin, creates an insulating sheath around fibres speeding up information through the CNS

  research found reduced myelination of white matter pathways in SZ patients compared to healthy controls
• grey matter:

  reduced volume of grey matter in SZ's brains especially in temporal and frontal lobes

  found those displaying negative symptoms have enlarged ventricles, they are thought to be the result of nearby parts of the brain not developing properly

  
• evaluation of neural correlates:

  findings are inconsistent so inconclusive

  MRI's made it possible to investigate living brain images

  cause and effect cannot be established with brain abnormalities as its uncertain whether structural abnormalities/reduced functioning predispose to SZ

  correlational data, there is a relationship between neural correlates in the brain and SZ
• evaluation of biological explanations

  inconsistent and there are contradictory findings

  cause and effect is difficult to establish as many P's have suffered from SZ for a long time, enlarged ventricles may be the result of taking antipsychotics

  biological explanations are reductionist in attempting to explain a complex multi-faced disorder at the levels of cells and genes

  deterministic: assumption its inherited and unavoidable

  diathesis-stress relationship may be at work, someone could be predisposed to SZ but its caused by environmental factors (interactionism)