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Biological Psychology – Biological Aetiology of Unipolar Depression
What is the biological aetiology of unipolar depression?
Answer:
The biological aetiology of unipolar depression refers to the biological factors that increase an individual’s risk of developing the disorder. These factors include genetics, neurotransmitter imbalances, hormonal changes, neurological abnormalities, and disturbances in circadian rhythms.
You should be able to discuss each of these biological influences in detail when answering reports or essay questions on unipolar depression.
How do genetics contribute to unipolar depression?
Answer:
Research suggests that unipolar depression has a genetic component, meaning that a predisposition to the disorder can be inherited.
Evidence includes:
How do neurotransmitters contribute to unipolar depression?
Answer:
Unipolar depression is associated with imbalances in several neurotransmitters, which are chemicals responsible for communication between neurons.
The neurotransmitters involved include:
How do hormones contribute to unipolar depression?
Answer:
The endocrine system releases abnormal levels of hormones during major depressive episodes.
The main hormones involved are:
How does neurology contribute to unipolar depression?
Answer:
Several neurological abnormalities have been linked to unipolar depression.
These include:
Reduced Monoaminergic Neuron Activity
Research by Drevets (2001) found:
Research by Öngür, Drevets and Price (1998) identified:
How do circadian rhythms and zeitgebers contribute to unipolar depression?
Answer:
Individuals with unipolar depression often experience disturbances in circadian rhythms, which regulate the body’s biological clock.
Common sleep changes include:
For example:
What are the main biological factors associated with unipolar depression?
Answer (Note Form):
Genetics
Physiology – Neurotransmitters
Physiology – Hormones
Neurology
Circadian Rhythms and Zeitgebers
Why is it important to understand the biological factors of unipolar depression?
Answer:
Understanding the biological factors helps explain how genetics, neurotransmitters, hormones, brain function, and sleep regulation contribute to depression. However, these biological influences do not act alone. They interact with psychological, social, and environmental factors, making depression best explained using a biopsychosocial approach.
Conclusion
The biological aetiology of unipolar depression involves a combination of genetic predisposition, neurotransmitter imbalances, hormonal abnormalities, neurological changes, and disturbances in circadian rhythms. Individuals with a family history of depression have an increased genetic risk, while abnormalities in serotonin, Substance P, norepinephrine, acetylcholine, dopamine, cortisol, melatonin, and 5-HIAA contribute to the symptoms of depression. Neurological findings include reduced monoaminergic neuron activity, increased activity in the amygdala and prefrontal cortex, decreased glial cells in the subgenual prefrontal cortex, and the possible effects of silent cerebral infarctions. Sleep disturbances and seasonal influences further contribute to the disorder. Although these biological factors play a major role, unipolar depression is best understood using a biopsychosocial approach, recognising that biological vulnerability interacts with psychological, social, and environmental influences to produce the disorder.
What is the biological aetiology of unipolar depression?
Answer:
The biological aetiology of unipolar depression refers to the biological factors that increase an individual’s risk of developing the disorder. These factors include genetics, neurotransmitter imbalances, hormonal changes, neurological abnormalities, and disturbances in circadian rhythms.
You should be able to discuss each of these biological influences in detail when answering reports or essay questions on unipolar depression.
How do genetics contribute to unipolar depression?
Answer:
Research suggests that unipolar depression has a genetic component, meaning that a predisposition to the disorder can be inherited.
Evidence includes:
- Monozygotic (identical) twins have a 46% chance of developing depression if their twin has been diagnosed.
- Dizygotic (fraternal) twins have a 20% chance of developing depression if their twin has been diagnosed.
How do neurotransmitters contribute to unipolar depression?
Answer:
Unipolar depression is associated with imbalances in several neurotransmitters, which are chemicals responsible for communication between neurons.
The neurotransmitters involved include:
- Serotonin
- Substance P
- Norepinephrine (noradrenaline)
- Acetylcholine
- Dopamine
- Mood
- Motivation
- Emotion
- Sleep
- Behaviour
How do hormones contribute to unipolar depression?
Answer:
The endocrine system releases abnormal levels of hormones during major depressive episodes.
The main hormones involved are:
- Cortisol – the body’s primary stress hormone.
- Melatonin – a hormone involved in regulating sleep and circadian rhythms.
How does neurology contribute to unipolar depression?
Answer:
Several neurological abnormalities have been linked to unipolar depression.
These include:
Reduced Monoaminergic Neuron Activity
- Decreased activity of monoaminergic neurons, which release serotonin and norepinephrine.
- Reduced neurotransmitter activity contributes to depressive symptoms.
Research by Drevets (2001) found:
- A 50–75% increase in blood flow and metabolism within the amygdala and prefrontal cortex.
- The amygdala is involved in regulating emotions.
- The prefrontal cortex is involved in the expression and regulation of negative emotions.
Research by Öngür, Drevets and Price (1998) identified:
- A 24% decrease in glial cells within the subgenual prefrontal cortex in individuals with major depression.
- Silent cerebral infarctions (strokes) may contribute to the development of late-onset depression.
How do circadian rhythms and zeitgebers contribute to unipolar depression?
Answer:
Individuals with unipolar depression often experience disturbances in circadian rhythms, which regulate the body’s biological clock.
Common sleep changes include:
- Shallow and fragmented sleep.
- Reduced slow-wave (delta) sleep.
- Increased Stage 1 sleep.
- Earlier and more frequent Rapid Eye Movement (REM) sleep.
For example:
- Seasonal changes may contribute to Seasonal Affective Disorder (SAD).
What are the main biological factors associated with unipolar depression?
Answer (Note Form):
Genetics
- Genetic predisposition can be inherited.
- Monozygotic twins:
- 46% chance if one twin is diagnosed.
- Dizygotic twins:
- 20% chance if one twin is diagnosed.
Physiology – Neurotransmitters
- Imbalances in:
- Serotonin
- Substance P
- Norepinephrine
- Acetylcholine
- Dopamine
- Low 5-HIAA associated with suicidal impulses.
Physiology – Hormones
- Abnormal endocrine activity.
- Increased abnormalities in:
- Cortisol
- Melatonin
Neurology
- Reduced monoaminergic neuron activity.
- Reduced serotonin and norepinephrine transmission.
- Amygdala:
- 50–75% increase in blood flow and metabolism.
- Prefrontal cortex:
- 50–75% increase in blood flow and metabolism.
- Subgenual prefrontal cortex:
- 24% decrease in glial cells.
- Silent cerebral infarctions (strokes) may cause late-onset depression.
Circadian Rhythms and Zeitgebers
- Shallow, fragmented sleep.
- Reduced slow-wave (delta) sleep.
- Increased Stage 1 sleep.
- Earlier and more frequent REM sleep.
- Seasonal influences.
- Seasonal Affective Disorder (SAD).
Why is it important to understand the biological factors of unipolar depression?
Answer:
Understanding the biological factors helps explain how genetics, neurotransmitters, hormones, brain function, and sleep regulation contribute to depression. However, these biological influences do not act alone. They interact with psychological, social, and environmental factors, making depression best explained using a biopsychosocial approach.
Conclusion
The biological aetiology of unipolar depression involves a combination of genetic predisposition, neurotransmitter imbalances, hormonal abnormalities, neurological changes, and disturbances in circadian rhythms. Individuals with a family history of depression have an increased genetic risk, while abnormalities in serotonin, Substance P, norepinephrine, acetylcholine, dopamine, cortisol, melatonin, and 5-HIAA contribute to the symptoms of depression. Neurological findings include reduced monoaminergic neuron activity, increased activity in the amygdala and prefrontal cortex, decreased glial cells in the subgenual prefrontal cortex, and the possible effects of silent cerebral infarctions. Sleep disturbances and seasonal influences further contribute to the disorder. Although these biological factors play a major role, unipolar depression is best understood using a biopsychosocial approach, recognising that biological vulnerability interacts with psychological, social, and environmental influences to produce the disorder.
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