OCR Psychology A Level Book 2 sample

Biochemical explanation of specific phobias Gamma-aminobutyric acid ( GABA ) is one of the most important inhibitory neurotransmitters in the central nervous system. Inhibitory neurotransmitters ‘switch off’ the next neuron, reducing the activity in the pathway. GABA counterbalances the excitatory action of the neurotransmitter glutamate . This means that it slows neuronal activity down in the glutamate pathways, which are implicated in memory and learning. People who have a phobia have decreased levels of GABA meaning that their neuronal firing in the glutamate pathways is higher, leading to the feelings of anxiety. Medications used to treat anxiety disorders often contain GABA, which reduces neuronal transmission in the brain and reduces feelings of anxiety. Research evidence Atul Pande et al . (1999) randomly assigned 69 patients with social phobia to an experimental group where they took a drug that increased levels of GABA for 14 weeks, or to a control group where they took a placebo drug. The researchers found a significant reduction in symptoms in the GABA group compared with the placebo group, suggesting that increased levels of GABA can lead to a reduction in anxiety. This supports the role that GABA plays in phobias. Biochemical explanation of schizophrenia Schizophrenia has been explained by the dopamine hypothesis which proposes that schizophrenia occurs because levels of the neurotransmitter dopamine (DA) are too high in the brain. The original and revised dopamine hypothesis The original dopamine hypothesis suggested that people with schizophrenia produce an excessive amount of dopamine in the brain, particularly in the limbic system . The revised dopamine hypothesis suggests that schizophrenia is not due to the production of excessive amounts of dopamine, rather that there is an excessive amount of dopamine receptors at the postsynaptic neuron and that these receptors are more sensitive than those in a neurotypical brain. This means that more dopamine is absorbed into the next neuron, which leads to an excess of dopamine in various pathways in the brain. This is particularly the case for the D2 subtype of dopamine receptors. This can occur due to a genetic dysfunction or due to some form of damage to the brain during development such as disease, infection or injury. Positive and negative symptoms The positive symptoms of schizophrenia have been linked with hypofunction (too much dopamine activity) in the mesolimbic pathway , which is responsible for motivation, emotion and reward. This can explain some of the positive symptoms such as unusual behaviours and perceptions. The negative symptoms have been linked to erratic dopamine function in the mesocortical pathway , which is responsible for executive function (mental control and self-regulation). This can explain the cognitive deficits and problems with affect experienced during a schizophrenic episode. mesolimbic pathway mesocortical pathway This diagram shows the main neurochemical pathways associated with the positive (left) and negative (right) symptoms of schizophrenia. Research evidence Philip Seeman (1987) reported several strands of evidence that provide support for the dopamine hypothesis, including: • Drugs that increase levels of dopamine increase some positive symptoms of schizophrenia such as hallucinations. • Antipsychotic drugs (dopamine antagonists that block dopamine receptors) reduce symptoms of schizophrenia. • Post-mortems of schizophrenic brains show higher density of D2 receptors than ‘neurotypical’ brains. Such evidence gives strong support to the role of dopamine in schizophrenia. Nucleus accumbens Ventral tegmental area Ventral tegmental area Frontal cortex There are lots of videos you can watch online about the role of neurotransmitters in mental illness. This is a particularly nice one: tinyurl.com/yanlfgms Drugs used to treat mental disorders such as depression, schizophrenia and phobias aim to counterbalance abnormal levels of neurotransmitters—and the benefits of such drugs support the biochemical explanations of mental illnesses. check your understanding 1. Outline the role of neurotransmitters in mental illness. 2. Briefly describe the role of each monoamine in the symptoms of depression. 3. Give one piece of evidence in support of biochemical explanations of depression. 4. Outline the original and revised dopamine hypothesis of schizophrenia. 5. Explain what happens in the mesocortical and mesolimbic pathways in a patient with schizophrenia. 6. Summarise Seeman’s arguments in support of the dopamine hypothesis. 7. Outline the role of GABA in phobias. 23 Background: The biochemical explanation of mental illness