Biological approach to mood disorders

Studies- Unipolar

Family Studies

  • Winokur- Found depression in just over 10% of first degree relatives compared to only 4.9% of control's relatives. Earlier found 50% of offspring showed symptoms of depression.
  • AO2-  Supports genetic factors BUT there could be an environmental factor of living with a depressed individual
  • McGuffin et al- Out of 200 pairs of MZ twins, 46% concordancy was found, 20% was found in DZ twins and only 10% in the general population
  • AO2- Supports genetic explanation that the more closely related you are the higher the risk BUT concordancy is not 100%, suggests other factors may be at play e.g. shared environment

Adoption Studies

  • Eliminate environmental factors
  • Wender et al- Investigated the families of depressed adoptees in DENMARK, the biological parents of depressed adoptees had a higher incidence of severe depression than the biological parents of non-depressed adoptees
  • AO2- Supports genetic explanation BUT only for severe depression
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The serotonin hypothesis- Unipolar

  • Argued that low activity of the neurotransmitters serotonin (5-HT) and noradrenaline (na) reduce firing at the synapse, resulting in the cognitive, behavioural and physical slowing of patients
  • Empirical evidence- Mc Neal found that the cerebrospinal fluid of depressed patients contains low levels of 5-HT and the urine of depressed patients contains low levels of na
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Brain structure and functioning in depressed patie

Frontal Cortex

  • Important in maintaining beliefs about goals and the means to achieve them
  • Depression is associated with lower than normal levels of activation in this area of the brian
  • MRI scans have shown a reduction in the size of frontal lobes of depressed patients

Limbic System

  • The frontal lobes help control the function of the limbic system
  • The amygdala is a part of the limbic system- increased activity in this area of the brain is thought to affect an individual's ability to process and judge threatening information, such information is interpreted negatively and believed to be more important/significant than it actually is


  • Cause and effect hasn't been found- does brain abnormality cause depression or vice versa?
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Genetic explanations for Bipolar

Biological abnormalities that cause Bipolar disorder

  • A decrease in the number of glial cells in the prefrontal cortex
  • Reduced activity in the prefrontal cortex (during the manic phase)
  • A decrease in the number of neurons in the hippocampus
  • A decrease in the size of the cerebellum

Family studies

  • Concordance rates- MZ= 70%, DZ= 23%
  • Close relatives of people with bipolar have a 7% likelihood of developing the disporder compared to 1% in the general population
  • Gershon- Relatives of bipolar patients have a higher risk (10-25%) of developing a mood disorder, but not necessarily bipolar disorder. This suggests unipolar and bipolar are the result of the same underlying problem- contradicts other research
  • The current belief is that the disorder is polygenic- caused by a number of genes rather than just one
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Explanations for Bipolar


  • High levels of noradrenaline have been implicated in mania
  • Post et al- raised levels of noradrenaline (na) in the cerebrospinal fluid of patients with mania, compared to controls
  • Telner- found manic symptoms subsided in patients after taking Reserpine (a drug used to treat blood pressure and known to reduce na levels
  • Low levels of serotonin (5-HT) have been implicated in mania- both depression and mania are related to low levels of 5-HT

The permissive theory

  • Low 5-HT levels results in a mood disorder, the na levels determine which one
  • Low5-HT + Low na = depression
  • Low5-HT + Highna = mania
  • Fluctuating na levels result in Bipolar 
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