Biological explanations Schizophrenia Biological explanations

Objectives To be able to… Describe the following biological explanations: General Genetic Link Neural Correlates Evaluate the explanations and answer exam questions.

What does this tell us about the causes of schizophrenia? Starter More than 100 genetic regions have been found to be involved in schizophrenia, many of which were not previously linked to the condition. Researchers say the finding uncovers the biological mechanisms causing the severe psychiatric disorder, and could lead to new treatments One hundred and eight locations (loci) in the human genome were linked to schizophrenia, 83 of which were previously unknown. The study, published in Nature, noted that many of the genes were expressed in the brain, thus 'providing biological plausibility for the findings'. Three-quarters of the loci coded for proteins, including the dopamine receptor (which most current schizophrenia medications target), as well other genes involved in brain signalling. What does this tell us about the causes of schizophrenia?

General Genetic link

Biological explanations Answer the questions below: pages 21-25 According to the general genetic hypothesis what increases your chance of developing the disorder? What is the likelihood of developing the disorder in the general population? According to Gottesman (1991), what is the percentage concordance rate of developing the disorder if one parent has the disorder? What methods are used to determine the genetic influence on schizophrenia? What does concordance rate mean? What were the findings of Gottesman’s study of MZ and DZ twins (1966)? What does this suggest about a genetic link in schizophrenia? What were the results of Kety’s adoption study? Why does it help our understanding of genetics to look at children brought up away from their biological parents? Name the specific gene(The Genome project) identified that causes schizophrenia.? There is strong evidence that shows schizophrenia is the result of multiple factors (genes + environment). This is also known as the diathesis stress model. How does the diathesis stress model explain schizophrenia?

Explanation 1: Genetics What does the bar graph to the left show about the relationship between genetics and schizophrenia? Write a conclusion! Challenge: How far do you think this data is valid? Gottesman (1991)

Biological: Always start with ‘Twin Studies’ Why start with Twin studies?….. explain Twin studies (eg. Gottesman, 1991) have identified strong concordance rates: MZ = 0.54 (54% risk) DZ = 0.18 (18% risk) General Population = 0.01 (1% risk) Point of interest: If your partner has schizophrenia your risk is twice that of the general population (2%: can you suggest why?)

Evaluation: page 24 Nature vs. Nurture Determinism Methodological Flaws Are MZ twins treated more similarly

There is overwhelming evidence for the idea that genetic factors make some people more vulnerable to developing schizophrenia than others. However, this does not mean that schizophrenia is entirely genetic. The diathesis-stress model may be a better way to explain the development of schizophrenia, where individuals inherit different levels of genetic predisposition, but ultimately it is environmental triggers that determine whether individuals go on to develop schizophrenia. Twin and family studies fail to consider the contribution of shared environmental influences on development of the disorder. If genes caused schizophrenia on their own, concordance rates between MZ twins would be 100%, which they are not. Twin studies also produce confusing evidence, with concordance rates for MZ twins ranging from 58% down to a slow as 11%.

Synaptic pruning Research has suggested that schizophrenia may be caused by a gene that causes excessive synaptic pruning. Read the article on pages 20 and 21 for a specific gene that may be related to schizophrenia.

Studies on family relatedness and schizophrenia Reading and activities in booklet pages 21- top of 25

Neural Correlates

Brain Areas If there is a genetic link how does this lead to the symptoms? It is likely that the genes are expressed in the brain. Influencing the structure and brain chemistry, particularly the dopamine pathways

Neural Correlates Neural correlates are measurements of the structure or function of the brain that correlate with an experience, in this case schizophrenia. Both positive and negative symptoms have neural correlates. Patterns of structure or activity in the brain that occur with a schizophrenic experience. As they occur simultaneously this could lead us to believe that the patterns observed are implicated in causing schizophrenia.

The Basal Ganglia - involved in movement and emotions The Basal Ganglia - involved in movement and emotions. Typical antipsychotics block the dopamine receptors here and can lead to movement side effects. Hippocampus - learning and memory which are impaired in schizophrenia Frontal Lobe - problems solving and reasoning skills. Problems here can lead to difficulty planning actions and organising thoughts. Occipital Lobe - can lead to difficulties in recognising emotion in others. Interpreting complex images and recognising motion. Limbic System - involved in emotion. Disturbance here can lead to agitation. Auditory System - linked to auditory hallucinations.

Enlarged Ventricles Read bottom of page 19 Johnstone et al (1976) first studied this using CT scans. They found significant ventricular enlargement in a group of chronic schizophrenia sufferers. This research has since been replicated. Then answer the following questions. 1. What is a ventricle? 2. What are they filled with? 3. If the ventricles are larger what does this mean for brain tissue? Synoptic – the brains of children suffering neglect and abuse often show reduced brain tissue and increased ventricles

Neural Correlates: Ventricles People with schizophrenia have abnormally large ventricles in the brain. Ventricles are fluid filled cavities (i.e. holes) in the brain that supply nutrients and remove waste. This means that the brains of schizophrenics are lighter than normal. The ventricles of a person with schizophrenia are on average about 15% bigger than normal (Torrey, 2002).

Suddath et al. (1990). Supporting evidence for the brain structure explanation comes from further empirical support from He used MRI (magnetic resonance imaging) to obtain pictures of the brain structure of MZ twins in which one twin was schizophrenic. The schizophrenic twin generally had more enlarged ventricles and a reduced anterior hypothalamus. The differences were so large the schizophrenic twins could be easily identified from the brain images in 12 out of 15 pairs. This suggests that there is wider academic credibility for enlarged ventricles determining the likelihood of schizophrenia developing.

Hallucinations and the Brain: Wernicke’s area Nearly always auditory. Wernicke's area may be involved. It may be that sufferers misinterpreted internal speech as coming from outside. This could be caused by overactivity in Wernicke's area.

Damage to the Cerebral Cortex. The dorsolateral prefrontal cortex. Supporting cells (glial) in this area may be affected in schizophrenia. Thin impairs problem solving and interpretation of deception.

Problems completing this task can be caused by underactivity in the frontal lobe. Patients with schizophrenia may find this task difficult

http://www.psytoolkit.org/experiment-library/experiment_wcst.html https://m.youtube.com/watch?v=kRN-TilDjX8

Neural Correlates: ventral striatum Avolition which involves motivation, has been associated with one of the main reward centres in the brain. The Ventral Striatum is crucial in the anticipation of reward. Juckel et al (2006) measured activity levels here and found lower levels of activity in schizophrenics compared to controls.

However, it does not answer the question of causation- does the unusual activity in that region cause the symptoms or does the disorder itself cause these brain differences? For example, it appears to be schizophrenics who do not respond to medication who mainly exhibit enlarged ventricles. This could mean that it is an effect of suffering from schizophrenia over a long period that leads to the physical brain damage rather than brain damage leading to schizophrenia. Ho et al. (2003) performed MRI scans on recent-onset schizophrenics and re-scanned them 3 years later. They found evidence of brain damage in the recent- onset patients, which worsened over time, especially in the frontal lobes, which correlated with an increase in the severity of their symptoms. This suggests brain damage does increase in schizophrenics over time.

Complete the chart

Evaluation of Brain Areas Improved technology allows us to study the brain. Clinical groups are used. Is it a cause or an effect? Write up these three points as evaluation of brain areas associated with schizophrenia.

A strength is that the research into enlarged ventricles has high reliability. The reason for this is because the research is carried out in highly controlled environments, which specialist, high tech equipment such as MRI and PET scans. These machines take accurate readings of brain regions such as the frontal and pre-frontal cortex, the basil ganglia, the hippocampus and the amygdale. This suggests that if this research was tested and re-tested the same results would be achieved. A second weakness of the neuroanatomical explanations is that it is biologically deterministic. The reason for this is because if the individual does have large ventricles then does it really mean that they will develop schizophrenia? This suggests that the dopamine hypothesis does not account for freewill.

Question Louise comes from a family with a history of schizophrenia, as both her grandfather and an aunt have been diagnosed with the disorder. Louise's father has recently died from cancer and she has moved out of her family home to start university. Although she has always been healthy in the past, she has begun to experience symptoms of schizophrenia, such as delusions and hallucinations. Using your knowledge of schizophrenia, explain why Louise is now showing symptoms of schizophrenia (4)

Model There is a history of schizophrenia in Louise's family so Louise could have inherited a genetic vulnerability to developing the disorder. This may have been triggered by the stressful life events she is experiencing. She has recently lost her father and she has left home to start university. These are both significant life events that could trigger a genetic predisposition to schizophrenia. This is an interactionist explanation for the development of schizophrenia and is known as the diathesis-stress model of mental illness.

ABC Task This is going to tough so look through your booklet and notes first.