Biological explanations

• genetic basis for sz

  schizophrenia runs in families.This is weak evidence in itself for a genetic link because family members tend to share an environment as well as many of their  genes. However,there have been systematic investigations of the extent to which greater genetic similarity between family members is associated with the likelihood of both developing schizophrenia.
• gottesman

  arge-scale family study.

  -found that the concordance rate for schizophrenia in MZ twins was 48% compared to 17% for DZ twins.
• candidate genes

  schizophrenia is polygenic.

  -different studies have identified different candidate genes so it appears that schizophrenia is aetiologically heterogeneous(different combinations of factors can lead to the condition).
• candidate genes

  Ripke carried out a huge study combining all previous data from genome-wide studies of schizophrenia.The genetic makeup of 37000 patients was compared to that of 113000 controls;108 separate genetic variations were associated with increased risk of schizophrenia.

  Genes associated with increased risk included those coding for the functioning of a number of neurotransmitters including dopamine.
• dopamine hypothesis

  Neurotransmitters-the brain’s chemical messengers appear to work differently in the brain of a patient with schizophrenia.Dopamine is widely believed to be involved.It is important in the functioning of several brain systems that may be implicated in the symptoms of schizophrenia.
• Hyperdopaminergia in the subcortex

  original version of the dopamine hypothesis focused on the possible role of high levels of dopamine in the subcortex(central areas of the brain).For example,an excess of dopamine receptors in Broca’s area(speech production) may be associated with speech poverty and the experience of auditory hallucinations.
• Hypodopaminergia in the cortex

  more recent versions of the dopamine hypothesis focus on abnormal dopamine systems in the brain’s cortex.Goldman-Rakic et al.(2004) identified a role for low levels of dopamine in the prefrontal cortex(responsible for thinking and decision making) in the negative symptoms of schizophrenia.
• neural correlates of schizophrenia

  are measurements of the structure/function of the brain that correlate with an experience.

  -both positive and negative symptoms have neural correlates.
• Neural correlates of positive symptoms:

  Avolition involves the loss of motivation.Motivation anticipates the anticipation of a reward .The ventral striatum is believed to be involved with this anticipation.So,abnormality in the ventral striatum may be involved in the development in avolition.

  -Juckel et al measured activity levels in the ventral striatum in schizophrenia and found lower levels of activity than those in controls.They observed a negative correlation between activity levels in the ventral striatum and the severity of negative symptoms.
• Neural correlates of positive symptoms:

  Allen et al scanned the brains of patients experiencing auditory hallucinations and compared them to a control group whilst they identified pre-recorded speech as theirs or others.Lower levels of activity in the superior temporal gyrus and anterior cingulate gyrus were found in the hallucination group that made more errors.
• glutamate

  • an excitatory neurotransmitter
  • found in low quantities in people with schizophrenia