OCR Psychology A Level Book 2 sample

Brain abnormality explanation of specific phobias Various brain structures have been linked with phobias . Prefrontal cortex integrates and responds to information coming from other areas, particularly the emotional centres of the brain. One of its roles is suppressing the fear response to stimuli. If the prefrontal cortex is not functioning effectively it fails to suppress the fearful urges from the amygdala. The amygdala detects and responds to threats in the environment. People who suffer from anxiety, including phobias, have a smaller amygdala, which has increased blood flow. This disruption to the structure and function of the amygdala is associated with the inability to control behavioural and physiological responses to fearful objects or situations, as seen in phobias. The hippocampus is largely involved in memory such as learned associations ( classical conditioning ). Reduced hippocampal functioning (reduced grey matter or damaged links) may mean that a person only recalls the link between a stimulus and the previous fearful experience, rather than neutral or positive feelings. Research evidence Fredrik Åhs et al. (2009) used PET scans to measure the cerebral blood flow in the amygdala and prefrontal cortex of patients with snake or spider phobia. They found that activity increased in the amygdala, particularly in the right hemisphere when the patients were shown objects that were fearful. This study also found reduced activity in the prefrontal cortex whilst a phobic stimulus was displayed, suggesting reduced behavioural control of the fear reactions that were elicited from the amygdala during fearful times. Eva Irle et al. (2010) demonstrated using MRI scans that 24 patients with social phobia had on average a 13% reduction in the size of their amygdala and 8% reduction in hippocampal volume compared with 24 healthy controls. These deficits in regional brain size link with the symptoms of phobias—difficulties in controlling emotional responses and recollection of previous contact with phobic objects. Brain abnormality explanation of schizophrenia Enlarged ventricles Research has found that people with schizophrenia have enlarged ventricles in their brain. There are four ventricles in the brain—cavities (spaces) that hold cerebrospinal fluid which provides nutrients to the brain and which protects the brain from damage. The ventricles do not have any cognitive functions. Reduced grey matter The enlarged ventricles lead to a reduction in the total amount of grey matter (functional neurons ) in the brain, particularly in these areas: • Temporal lobes (verbal and acoustic memory), loss of grey matter may explain auditory hallucinations. • Frontal lobes (planning and coordination), loss may explain incoherent speech and perceptual disturbances such as delusions. • The thalamus (integrating sensory and motor information), loss may lead to auditory and verbal hallucinations. Smaller brain size Patients with schizophrenia have a reduced overall brain size, with less grey matter in total compared with neurotypical brains. The longer that patients have had schizophrenia, the less grey matter there is in their brain. This reduction in grey matter stops when patients take antipsychotic medications , suggesting that the reduced grey matter is associated with aspects of the disorder. Research evidence According to research by Hilleke Hulshoff Pol et al. (2002), which compared 159 people with schizophrenia with 158 ‘healthy’ individuals, there can be up to a 30% increase in the size of the ventricles of patients with schizophrenia. Larger ventricles mean less grey matter in the brain—which means less functionality within the brain. A meta-analysis by Sander Haijma et al. (2013) analysed 317 studies that conducted MRI scans on a total of over 100 areas of the brain, using a total sample size of 8,327 patients with schizophrenia. This meta-analysis suggested that people with schizophrenia have brains that are 2.6% smaller than neurotypical brains. In addition to this the MRI scans in Haijma et al .’s review found that areas of the brain such as the thalamus (which deals with sensory and motor integration and is under the temporal lobe) were even smaller in people with schizophrenia who had not received any medication for their condition. Cross-section of the brain showing normal ventricles (above) compared to enlarged ventricles (below). Martha Shenton et al. (2001) reviewed MRI studies of people with schizophrenia and found that 80% of studies showed ventricular enlargement. This means the ventricles in the brain were bigger in patients with schizophrenia than neurotypical patients. A number of the studies on this spread used scanning techniques. Watch online videos showing how MRI scans are done. For example, this clip discusses an MRI scan of a pair of twins, one of whom has schizophrenia: tinyurl.com/y8pcolnm This clip shows what it is like to have an MRI scan: tinyurl.com/yb6pparv check your understanding 1. Outline how the ventricles in the brain may play a role in schizophrenia. 2. Explain the role of the prefrontal cortex in depression. 3. Outline Sheline et al. ’s research and explain what it tells us about brain abnormality as an explanation of mental illness. 4. Describe how brain abnormality can explain phobias. Ventricles 27 Background: Brain abnormality as an explanation of mental illness