BIOLOGICAL EXPLANATIONS OF DEPRESSION
The Unit 2 Exam expects you to know about one biological explanation of a disorder other than schizophrenia: here, unipolar depression.
You are also expected to understand a biological treatment for depression which is linked to these explanations. There's a strong biological link with depression, which seems to run in families. Elliot Gershon (1990) reviewed 10 family studies and found that the rate of depression was 2-3 times higher in first degree relatives of people with depression (their parents, siblings and children) compared to the general population.
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DEPRESSION & THE FUNCTIONS OF NEUROTRANSMITTERS
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Among the monoamines, serotonin is particularly important. One of its jobs is to regulate the other neurotransmitters. Without the regulation provided by serotonin, brain functioning becomes erratic.
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High levels of serotonin would boost noradrenaline and dopamine, producing a hyper-alert and psychotic state of mind. This is linked to another condition called bipolar disorder - also known as manic-depression.
Depressed mood states can be caused by low levels of noradrenaline or dopamine, but the main culprit is the serotonin, which is controlling the other two. A particular gene called 5-HTT has been linked to regulating serotonin levels. People with variations of the 5-HTT gene that are under-active seem more likely to suffer depression after stressful life events.
Rosenthal's diathesis-stress model explains that a gene that produces a mental disorder can be "triggered" by a stressful environment. |
However, the problem might not be low levels of the neurotransmitters themselves. It might be a problem with the receptors that pick up the neurotransmitters when they cross the synapse from one neuron to another. If there aren't enough receptors - or if the receptors aren't working properly - this will have the same effect as a lack of the neurotransmitter.
Research focuses on a chemical called monoamine oxidase A (MAO-A), which is a chemical that removes monoamines from the synapse. This is an important brain function called "re-uptake" that recycles neurotransmitters when they don't appear to be needed.
However, if there is too much MAO-A in the synapse, it will remove monoamines that are needed, starving the brain of serotonin, noradrenaline and dopamine, leading to symptoms of depression. This is the basis for a lot of antidepressant drugs, which inhibit (reduce) the activity of MAO-A. This leads to more monoamine activity and a reduction in the symptoms of depression. |
The MAO-A is like "Pac Man", gobbling up excess monoamines. Now imagine Pac Man out of control!
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You can compare this to the "synaptic pruning" explanation for schizophrenia. In both cases, a normal healthy process in the brain goes too far, producing unhealthy results.
MAO-A is also linked to aggression. When MAO-A levels are too LOW, people experience violent impulses (Brunner et al., 1993)
MAO-A is also linked to aggression. When MAO-A levels are too LOW, people experience violent impulses (Brunner et al., 1993)
Fantastic poster that covers features and symptoms of depression as well as biological explanations
APPLYING BIOLOGICAL EXPLANATIONS OF DEPRESSION
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EVALUATING BIOLOGICAL EXPLANATIONS
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EXEMPLAR ESSAY
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