Research on teen depression has lagged far behind research on adult depression. As a result, there is little conclusive evidence about the biology of teen depression and how it might differ from the biology of depression in adults.

Biology of Depression: The Monoamine Theory

The monoamine theory was developed in the 1950s after a group of scientists accidentally discovered that a drug called “reserpine” could actually cause depression. These scientists realized that reserpine had the effect of producing a shortage of certain monoamines (neurotransmitters that contain only one amino group) in the brain. They concluded that depression was the result of the under-activity of three monoamines in particular:

  • Dopamine
  • Norepinephrine (also known as noradrenaline)
  • Serotonin.

Biology of Depression and the Rest of the Brain

Since the development of the monoamine theory, depression research has uncovered more to the story of depression. Imbalances of dopamine, norepinephrine and serotonin do appear to be linked to depression, but other areas and functions of the brain are also affected by depression. Research into the link between depression and brain activity has yielded the following results:

  • The Hippocampus: This area of the brain oversees neurogenesis in particular parts of the brain. Neurogenesis is the process by which new neurons are formed in the brain. People who are depressed exhibit lower rates of neurogenesis.
  • The Hypothalamus: This part of the brain carries out a variety of important functions, including the secretion of hormones. Research shows that the hypothalamus triggers higher levels of stress hormones in individuals with depression.
  • The Prefrontal Cortex: Located in the frontal lobes, just behind the forehead is the prefrontal cortex. Medical researchers believe that this area of the brain plays a role in regulating emotion. Brain scans reveal that people who are depressed have lower than average rates of activity in this area of the brain.
  • The Ventromedial Cortex: This part of the prefrontal cortex plays a role in decision-making and mood changes. This area of the brain is much smaller in people with depression.

The Biology of Teen Depression

The information above outlines what researchers have uncovered about the biology of depression by studying depression in adults. Researchers are less certain about the biology of teen depression.

Children and adolescents go through a number of dramatic physiological changes (like hormone and brain development) that could have a significant impact on the biology of depression in teens. For example, there is mounting evidence to support the link between brain development and mental disorders. According to the National Institute of Mental Health, the timing and growth rates of certain areas of a developing adolescent brain can impact the likelihood of depression and other mental disorders later in life.


Centre for Addiction and Mental Health Staff. (2010). Critical brain chemical shown to play role in severe depression. Retrieved May 5, 2010, from the Centre for Addiction and Mental Health Staff website: backgrounders/depression_brain_levinson.html.

Lundbeck Institute Staff. (n.d.) Depression – aetiology. Retrieved May 5, 2010, from the Lundbeck Institute website:

National Institute of Mental Health Staff. (2008). Clues to role of brain development as risk for mental disorders may also lead to better treatments. Retrieved May 13, 2010, from the National Institute of Mental Health website:

Nemade, R. et al. (n.d.) Depression: major depression & unipolar varieties. Retrieved May 5, 2010, from the website:

 Posted on : June 26, 2014