biological explanation of schizophrenia

• Factors in the biological explanation of schizophrenia:

  Genetic vulnerability

  Neurochemical explanations

  Neural correlates ( brain structure / function )
• Gottesman ( 1991 ) conduced a large scale family study. It was found that there is a strong relationship between the degree of genetic similarity and shared risk of schizophrenia
• Candidate genes in schizophrenia - any gene thought likely to cause a disease. This is because it is located in a particular chromosome region suspected of being involved in the disorder.
• Schizophrenia is polygenic as it requires a number of factors to work in combination
• Ripke et al ( 2014 ) found 108 separate genetic variations associated with the increased risk of schizophrenia. They included those coding for the function of a number of neurotra, including dopamine.
• Dopamine is a chemical substance ( neurotransmitter ) manufactured in the brain that transmits messages between neurons ( brain cells )
• Neurochemical explanations - dopamine hypothesis:

  Calabresi et al reported the role of dopamine in modulation of behaviour and cognition, voluntary movement, motivation, punishment and reward, working memory, learning, sleep, dreaming, mood, attention.

  Dopamine appears to work differently in patients with schizophrenia.

  It is important in the function of several brain systems that may cause symptoms of schizophrenia
• Dopamine is important in the functioning of several brain systems that may cause symptoms of schizophrenia:

  the cortex

  the subcortex
• Dopamine levels for schizophrenia:

  Hyperdopaminergia - excessive levels of dopamine in the subcortex and broca’s area makes positive symptoms

  Hypodopaminergia - low levels of dopamine in the prefrontal cortex makes negative symptoms
• Hyperdopaminergia - excessive levels of dopamine in the subcortex and broca’s area makes positive symptoms
• Hypodopaminergia - low levels of dopamine in the prefrontal cortex makes negative symptoms
• Gottesman found that the more genetics shared, the higher the likelihood of developing schizophrenia if the other individual has it.

  MZ twins = 48 %

  DZ twins = 17 %
• Candidate genes - specific genes causing disorder
• Neural correlates - patterns of structure or activity in the brain that occur with a schizophrenic experience
• As neural correlations occur simultaneously, we could believe that the patterns observed are implicated in causing schizophrenia
• Avolition, which involves motivation, has been associated with one of the main reward centres in the brain. The Ventral Striatum is crucial for anticipation of reward. Juckel ( 2006 ) found lower levels of activity here in schizophrenics compared to the control.
• As the levels of activity in the ventral striatum decreases, the levels of avolition increase.
• Neural correlates positive symptoms - Allen et al ( 2007 ) brain scans of patients with auditory hallucinations compared to a control group. They had to identify pre recorded speech as their or someone else's voice.

  There was lower activation levels in the superior temporal gyrus and anterior cingulate gyrus found in the hallucination group, as well as more errors. Reduced activity here could be a neural correlate of auditory hallucinations
• The superior temporal gyrus is responsible for processing sounds
• The anterior cigulate cortex has been implicated in several cognitive functions such as empathy, impulse control, emotion and decision making
• Neural correlates negative symptoms - Juckel et al ( 2006 ) measured activity levels in the ventral striatum in schizophrenia and found lower levels of activity in them compared to the controls. There was also a negative correlation between activity in the ventral striatum and the severity of negative symptoms
• Negative symptoms neural correlations - ventral striatum
• Positive symptoms neural correlations - superior temporal gyrus, anterior cingulate cortex
• AO3. The genetic explanation for schizophrenia is not completely reliable. Genes are only partially responsible. If genes were completely responsible, we would see a 100 % concordance rate between MZ twins. This means that schizophrenia cannot completely be explained by genes and it may be that if an individual has a predisposition to schizophrenia it simply makes the individual more at risk of developing the disorder.
• AO3. The genetic explanation is biologically reductionist. Schizophrenia is a multi factorial trait as it is the result of multiple genes and environmental factors. This suggests that the research into gene mapping is over simplistic as schizophrenia is not due to one single gene. 
• AO3 The neurochemical explanation does not account for all schizophrenia patients. Noll ( 2009 ) argues that one third of patients do not respond to drugs which block dopamine. This means that other neurotransmitters may be involved, and we cannot assume that dopamine is a cause for schizophrenia.
• AO3. The neurochemical explanation for schizophrenia is biologically deterministic. If an individual has excessive amounts of dopamine then doesn’t mean that they will develop schizophrenia. The dopamine hypothesis does not account for free will.
• AO3. The neural correlates explanation of schizophrenia is reliable. Related research takes a scientific approach, carried out in highly controlled environments with both specialists and high technology equipment such as MRI and PET scans. This means that there is physical evidence, making it more reliable