Depression is a mood disorder that causes a continuous low mood and loss of interest in life. Precursors (predisposing factors) for the development of depression can be:

  • Stressful events like the break-up of a relationship or financial trouble
  • A family history of depression
  • Physical illness, such as a stroke or heart attack
  • Stressful or traumatic events in childhood can lead to depression later in life
  • Certain medications can cause depression in some people
  • Social isolation – i.e. having no friends or family near you.
  • Age, gender, ethnicity

Individuals may experience negative thinking, morbid thoughts, rumination of concerns, and catastrophic thinking. Self cares may be neglected and there may be an inability to function in everyday life. Suicidal ideation and self harm may emerge during depression.



Depression can be attributed to dysfunctional neurotransmitters within the brain: serotonin, noradrenaline, dopamine, glutamate, and GABBA.

This article goes into depth with the role of neurotransmitters, stress hormones and brain function involved in the development of depression

In depression, the hypothalamic-pituitary-adrenal axis is up-regulated (increased response to stimuli). negative feedback loops are also down regulated (reduced response to stimuli). This leads to overactivation of the HPA, resulting in excessive release of the stress hormone cortisol. Excessive cortisol release causes dysfunction of serotonin, noradrenaline and sleep regulation. Many other cerebral structures have also been associated with depression.

Figure 1: Areas of the brain affected by depression

Areas of the brain affected by depression

Amygdala: The amygdala is part of the limbic system, a group of structures deep in the brain that’s associated with emotions such as anger, pleasure, sorrow, fear, and sexual arousal. The amygdala is activated when a person recalls emotionally charged memories, such as a frightening situation. Activity in the amygdala is higher when a person is sad or clinically depressed. This increased activity continues even after recovery from depression.

Thalamus: The thalamus receives most sensory information and relays it to the appropriate part of the cerebral cortex, which directs high-level functions such as speech, behavioral reactions, movement, thinking, and learning. Some research suggests that bipolar disorder may result from problems in the thalamus, which helps link sensory input to pleasant and unpleasant feelings.

Hippocampus: The hippocampus is part of the limbic system and has a central role in processing long-term memory and recollection. Interplay between the hippocampus and the amygdala might account for the adage “once bitten, twice shy.” It is this part of the brain that registers fear when you are confronted by a barking, aggressive dog, and the memory of such an experience may make you wary of dogs you come across later in life. The hippocampus is smaller in some depressed people, and research suggests that ongoing exposure to stress hormone impairs the growth of nerve cells in this part of the brain.

Retrieved from
 Read the full article for more information.


Assessment and diagnosis

DSM-IV Criteria for Major Depressive Disorder (MDD)

  • Depressed mood or a loss of interest or pleasure in daily activities for more than two weeks.
  • Mood represents a change from the person’s baseline.
  • Impaired function: social, occupational, educational.
  • Specific symptoms, at least 5 of these 9, present nearly every day
  • 1.Depressed mood or irritable most of the day, nearly every day, as indicated by either subjective report
  • (e.g., feels sad or empty) or observation made by others (e.g., appears tearful).
  • 2.Decreased interest or pleasure in most activities, most of each day
  • 3.Significant weight change (5%) or change in appetite
  • 4.Change in sleep: Insomnia or hypersomnia
  • 5.Change in activity: Psychomotor agitation or retardation
  • 6.Fatigue or loss of energy
  • 7.Guilt/worthlessness: Feelings of worthlessness or excessive or inappropriate guilt
  • 8.Concentration: diminished ability to think or concentrate, or more indecisiveness
  • 9.Suicidality: Thoughts of death or suicide, or has suicide plan

Signs and symptoms

  • Sadness
  • Inactivity
  • Lack of desire to socialise leading to withdrawal
  • Difficulty thinking
  • Difficulty concentrating
  • Reluctance to make decisions
  • Problem sleeping
  • Changes in appetite
  • Fatigue
  • Agitation
  • Feelings of despair
  • Recurrent thoughts of death

This issue of Best Practice Journal, discusses the assessments required in order to recognize and diagnose adults whom are experiencing depression.


This lecture from Robert Sapolski is a good way to link all the information together to get a thorough understanding of the development of depression.

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American Psycological Association. (2016). Diagnostic and statistical manual of mental     disorders:  Fifth Edition. Retrieved from

Mental Health Foundation of New Zealand.(2017). Depression. Retrieved from

Craft, J., & Gordon, C. (2015). Understanding pathophysiology (2nd ed). Sydney, Australia: Mosby Elsevier.