Biological explanations of depression

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  • Biological Explanations
    • Serotonin
      • AO1
        • An imbalance of neurotransmitters can lead to depression
        • Serotonin, noradrenalin and dopamine are important in the functioning of the limbic system and amygdala
          • Which play a significant role in the regulation of drives such as appetite and the control of emotion
        • Depression occurs when there is not enough serotonin in the synaptic gap to bind the receptors
        • This causes a chemical imbalence in the dendrite of the next neuron, and depressive symptoms occur
      • AO2
        • 1) Delgado et al.
          • Gave depressed patients a special diet that lowered their levels of one of the precursors of serotonin - tryptophan
          • The majority of paitents experienced a return of their depressive symptoms, which disappered after the diet returned to normal
          • This suggests that serotonin levels play an important part in the prescence of depressive symptoms
            • Correlational - doesn't shown cause and effect
        • Ruhe et al.
          • Serotonin may play a role but not necessarily a causal one
          • Patients who were in remission from depression experienced a brief lapse of symptoms when a tryptophan-deficient amino acid mixture
          • However, this was only evident in patients who had a history of depression, ppts. who had never had depression nor a family history experienced no such relapse
            • Suggests that lowering serotonin levels does not induce depression in everyone and serotonin may only play a minor role in the development of depression
        • Thase et al.
          • Claimed that depression was caused by an overall imbalance of several neural transmitters (incl. serotonin, dopamine, noradrenalin and acetylcholine)
          • Serotonin appears particularly important because it may act as a neuromodulator (controller) of a variety of brain systems
          • When serotonin levels are low, activity in the other systems is disrupted and causes depressive symptoms
          • This suggests the serotonin explanation is too simplistic
    • Genetics
      • AO1
        • Depression appears to run in families, therefore there may be a genetic cause
        • Can be investigated through the use of adoption studies - if there is a genetic link then biological parents should show higher rates of depression than adopted ones
        • Also twin studies: monozygotic and diztgotic twins are studied to see if the other twin has been, or might be diagnosed with depression
          • If there is a gentic link there should be a higher concordence rate between MZ than DZ twins
      • AO2
        • Wender et al.
          • Studied biological relatives of adopted individuals who had been hospitalised for severe depression
          • They found a much higher instance of severe depression in the biological relatives than in the biological relatives of a non-depressed control group
          • This suggests that there is a heritable component to depression and implies that gentics are involved in the development of depression
        • Bierut et al.
          • Carried out a twin study of 2262 twin pairs in Australia, and found concordence rates of 36% and 44% in MZ twins
          • They claimed that environmental factors played a larger role
          • This is supported by the idea of genes of diathesis, which suggests that people have a genetic disposition for depression that interacts with environmental stressors to produce a depressive reaction
          • Kendler et al.
            • Found that negative symptoms of depression (sleep disturbance, weight changes etc) seemed to be more influenced by heredity than by stressful events
              • However, the actual no. of depressive episodes was linked to life events.
                • This suggests that there may be a genetic component operating as a predisposing factor, with additional components (life events) leading to depression
        • Concordence rates
          • Lack of a 100% concordence rate, which would be present if genetics were the sole cause of depression
          • Genetics appear to be a risk factor, but are not sufficient to provide a complete explanation in isolation

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