Mood Disorders

The Structure of Mood Disorders

  • Unipolar mood disorder: Only one extreme of mood is experienced
    • E.g., only depression or only mania
    • Depression alone is much more common than mania alone
  • Bipolar mood disorder: Both depressed and elevated moods are experienced
    • E.g., some depressive episodes and some manic or hypomanic episodes

Prevalence of Mood Disorders

  • Worldwide lifetime prevalence of MDD: 16%
    • 6% have experienced major depression in last year
  • Sex differences
    • Females are twice as likely to have major depression
    • Bipolar disorders approximately equally affect males and females
    • Women more likely to experience rapid cycling
    • Women more likely to be in depressive period
  • Occurs less often in prepubertal children
  • Rapid rise in adolescents
  • Adults over 65 have about 50% less prevalence than general population
  • Bipolar same in childhood, adolescence, and adults
  • Prevalence of depression seems to be similar across subcultures
  • Across Cultures
    • Similar prevalence among U.S. subcultures, but experience of symptoms may vary
    • E.g., some cultures more likely to express depression as somatic concern
    • Higher prevalence among Native Americans: Four times the rate of the general population

Life Span Developmental Influences

  • 3-month-olds can show depressive symptoms
  • Young children typically don’t show classic mania or bipolar symptoms
  • Mood disorder may be misdiagnosed as ADHD
  • Children are being diagnosed with bipolar disorders at increasingly high rates
  • Depression in elderly between 14% and 42%
    • Co-occurrence with anxiety disorders
    • Less gender imbalance after 65 years of age

Causes

  • Family studies
    • Risk is higher if relative has a mood disorder
    • Relatives of bipolar probands are more likely to have unipolar depression
  • Twin studies
    • Concordance rates are high in identical twins
    • Two to three times more likely to present with mood disorders than a fraternal twin of a depressed co-twin
    • Severe mood disorders have a strong genetic contribution
    • Heritability rates are higher for females compared to males
    • Some genetic factors confer risk for both anxiety and depression
  • Neurotransmitter systems
    • Serotonin and its relation to other neurotransmitters
    • Serotonin regulates norepinephrine and dopamine
    • Mood disorders are related to low levels of serotonin
    • Permissive hypothesis: Low serotonin “permits” other neurotransmitters to vary more widely, increasing vulnerability to depression
    • The endocrine system
    • Elevated cortisol
    • Stress hormones decrease neurogenesis in the hippocampus > less able to make new neurons
    • Sleep disturbance
    • Hallmark of most mood disorders
    • Depressed patients have quicker and more intense REM sleep
    • Sleep deprivation may temporarily improve depressive symptoms in bipolar patients

Psychological Dimensions

  • Stressful life events
    • Stress is strongly related to mood disorders
    • Poorer response to treatments
    • Longer time before remission
    • Context of life events matters
    • Gene-environment correlation: People who are vulnerable to depression might be more likely to enter situations that will lead to stress
    • The relationship between stress and bipolar is also strong
  • The learned helplessness theory of depression
    • Lack of perceived control over life events leads to decreased attempts to improve own situation
    • First demonstrated in research by Martin Seligman
    • Negative cognitive styles are a risk factor for depression