Biological explanations of schizophrenia

• Biological explanations of scizophrenia?

  • Biological explanations of schizophrenia look at biological factors linked to schizophrenia
  • These include genetics, neural abnormalities, and abnormalities in dopamine
• Genetic explanation?

  • the genetic explanation of schizophrenia looks at hereditary factors like genes that contribute to the development of schizophrenia
• Twin studies for genetics?

  Gottesman (1991)

  • looked at how different relationships to someone w schizophrenia are linked w risk of developing schizophrenia
  • He found the closer the genetic relationship the greater the risk
  • The concordance rate for identical twins is 48% whereas non-identical twins is 17%
  • This supports the idea that genetics play a role in developing schizophrenia

  Cardno et al (1999)

  • found identical twin had a concordance rate of 40.8%
  • whereas non identical had concordance rate of 5.3%
• Adoption studies for gentic?

  Tienari et al (1985)

  • conducted longitudinal study comparing adopted whose biological mother was schizophrenic and a control group of adoptees who's mothers weren't
  • Found children of schizophrenia mothers were more likely to develop schizophrenia than controls

  Kety and Ingraham (1992)

  • found adoptees whose biological parents had schizophrenia were 10x more likely to develop it than control group

  Studies like these are useful because it separates environmental factors like schizophrenia being passed on through environmental factors = genetic explanation
• Supporting evidence of genetic explanations?

  • Twin and adoption studies because they show that being closely related (thus having similar genes) to someone w schizophrenia increases the likelihood of suffering aswell
• Strengths of genetic explanations of schizophrenia?

  • Multiple genes - its unlikely that there is a single gene responsible for schizophrenia, multiple genes likely combine to increase a person risk

  Ripke et al (2014)

  • combined 36,000 schizophrenia patients and found 108 different genetic variations that were correlated
  • many of these variations were related to dopamine transmission
  • combine w dopamine hypothesis for a holistic explanation
• Weaknesses of genetic explanations of schizophrenia?

  • other factors play apart - if it was only based on genetics then concordance rate between identical twins would be 100%
  • Methodological issues w twin studies - they often assume twins had identical upbringings and any difference must be explained by genetics, however environmental factors play a role too e.g. looking identical may cause them to be treating the same by parents/teachers = higher concordance rates for identical twins
• Neural explanations of schizophrenia?

  • the neural explanation of schizophrenia looks at correlations among the brain structure of people with Schiz
  • Researchers use brain examining techniques to compare the brains of schizophrenic people to identify different structures that may cause schizophrenia
• Studies of enlarged ventricles and schizophrenia?

  • Enlarged ventricles: several studies have found correlations between enlarged ventricles in brain and schizophrenia, like Johnstone et al (1976)
  • Andreasen et al (1982) found enlarged ventricles are particularly linked with negative symptoms of schizophrenia
• Studies of reduced grey matter and cortical thinning?

  Boos et al (2012)

  • compared MRI scans of 155 schizophrenic patients, 186 non-schizophrenic family members and 122 non schizophrenic controls
  • Found schizophrenic patients had reduced grey matter and cortical thinning compare to the non-schizophrenics
  • Further supports the existence of a neural basis for schizophrenia
• Studies of Facial emotion processing and schizophrenia?

  • A common symptom of schizophrenia is difficulty perceiving emotions

  Li et al (2010)

  • A meta analysis by Li looked at fMRI scans of schizophrenic patients and non-schizophrenic controls during facial expression processing tasks
  • The researchers found people w schizophrenia have reduced activity in the bilateral amygdala and right fusiform gyri compared to controls
  • Suggesting a neural basis for this symptom
• Supporting evidence of neural explanations?

  • several neural explanations of schizophrenia mentioned that demonstrate the correlation between neural structures and schizophrenia
• Conflicting evidence to neural explanations of schizophrenia?

  • altho several studies have found correlations between enlarged ventricles and schizophrenia there are many exceptions
  • There are many people with enlarged ventricles who don't have schizophrenia, and there are many people without large ventricles who DO have schizophrenia
• Weaknesses of neural explanations of schizophrenia?

  • Correlation vs causation - altho there are correlations between schizophrenia and certain neural patterns, it can be difficult to determine whether abnormal brain functioning causes schizophrenia symptoms or whether its an affect of schizophrenia
  • e.g. does reduced activity in the bilateral amygdala of schizophrenic patients cause difficulties in emotional processing, or do reduced emotional processing result in reduced blood flor and activity in the bilateral amygdala?
• The Dopamine Hypothesis?

  • The dopamine hypothesis explains schizophrenia as a result of abnormal activity of the neural transmitter dopamine
  • Became popular in 70s when studies e.g. seeman et al (1976), Creese et al (1976), and synder (1976) reported that several drugs that reduce schizophrenia symptoms are dopamine receptor antagonists (reduce dopamine activity)
• Evidence supporting dopamine hypothesis - dopamine antagonists ?

  • Dopamine antagonist - dopamine antagonists (drugs that increase dopamine) such as amphetamines can induce schizophrenic symptoms in schizophrenics

  Systematic review by curran et al (2004)

  • found amphetamine makes schizophrenia symptoms worse

  Mcketin et al (2013)

  • found non-schizophrenic methamphetamine addicts demonstrated a 5 fold increase in schizophrenia like symptoms when using

  Randrup and munkvad (1966)

  • were able to induce schizophrenic behaviour in rats w amphetamines and reverse symptoms with dopamine antagonists
• Evidence supporting the dopamine hypothesis - Post mortem?

  Bird et al (1979)

  • used post-mortems to compare dopamine levels in the brains of 50 schizophrenic patients w 50 non schizophrenic controls
  • The schizophrenic patients had increased dopamine concentrations in some areas of the brain compared to controls
• Evidence supporting the dopamine hypothesis - Brain scans?

  Lindstrom et al (1999)

  • compared PET scans of 12 schizophrenic patients w 10 controls and found the schizophrenic patients had increased dopamine activity in the striatum and parts of the prefrontal medial cortex

  Alves et al (2008)

  • A review of MRI scans found support for the dopamine hypothesis
• Revised dopamine hypothesis?

  • over the years the dopamine hypothesis has been refined, its not as simple as high dopamine = schizophrenia
  • Instead, research suggests schizophrenia is linked w high dopamine activity in some areas of the brain (sub cortex) but low dopamine activity in other areas (prefrontal cortex)
• Conflicting evidence of the dopamine hypothesis of schizophrenia?

  Farde et al (1990)

  • Compared brain scans of 18 schizophrenia patients w 20 non-schizophrenic controls
  • Found no difference in dopamine activity between two groups

  Haracz (1982)

  • found little evidence to support the dopamine hypothesis
• Weaknesses of the dopamine hypothesis of schizophrenia - other neurotransmitters ?

  • Evidence suggests other neurotransmitters besides dopamine are involved in development of schizophrenia, e.g glutamate and serotonin

  Marsman et al (2013)

  • conducted meta-analysis of brain scans
  • found decreased glutamate activity in schizophrenic patients compared to controls,
  • evidence drugs that alter glutamate activity can successfully treat schizophrenia
  • P.S glutamate hypothesis doesn't contradict dopamine hypothesis=both involved?
  • Serotonin also, suggested by efficiency of atypical antipsychotic drugs
• Weaknesses of the dopamine hypothesis of schizophrenia - Bias?

  David Healy (2002)

  • argues that pharmaceutical companies exaggerated the dopamine hypothesis of schizophrenia to sell more drugs
  • The overly-simplified hypothesis that schizophrenia is caused by high dopamine makes it easy to market antipsychotic drugs as 'cures' for schizophrenia