In the past, medical professionals believed that depression was the result of chemical imbalances in the brain. Although this is indeed part of the story, research has revealed that an explanation of the biology of depression is much more complex.

The Monoamine Theory: Depression Due to Chemical Imbalances

The monoamine theory suggests that depression is the result of too little activity of certain monoamines (acting as neurotransmitters) in the brain. Scientists developed the monoamine theory in the 1950s after observing that treatment with the drug reserpine caused depression in some cases. This drug had the resultant effect of producing a shortage of monoamines, such as dopamine, norepinephrine and serotonin. This discovery led to the development of several antidepressant drugs (called monoamine oxidase inhibitors) that focused on regulating the activity of these monoamines.

ThereÕs More to the Biology of Depression

Since the development of the monoamine theory, depression research has shown that this theory only provides a partial explanation for depression and its effect on the brain. Depression does indeed appear to be linked to imbalances of dopamine, norepinephrine and serotonin, but research suggests that other neurotransmitters, such as glutamate and gamma-aminobutyric acid (GABA), may also be linked to depression.

Nor is the biology of depression only linked to the activity of neurotransmitters. Research shows that other areas and functions of the brain are also associated with depression.

The Biology of Depression in the Hippocampus

The process by which new neurons are formed in the brain is called “neurogenesis.” This activity has been recently demonstrated in the hippocampus. New studies from Columbia University show that people who experience chronic stress and depression show evidence of lower rates of neurogenesis in the hippocampus. The concept of neurogenesis is relatively new, challenging the notion that no new neurons can grow after birth.

Hormones and the Hypothalamus

Hormones are also involved in the biology of depression. Hormones are produced by the endocrine system, which is linked, along with the nervous system, to the hypothalamus in the brain. The hypothalamus is involved in regulating some of the bodyÕs regulatory processes, such as blood pressure and body temperature. The hypothalamus also secretes hormones. A University of Bristol study shows that individuals with severe depression trigger the hypothalamus to increase the overall amount of corticosteroids in the bloodstream.

Depression and Brain Activity in the Frontal Lobes

The prefrontal cortex is located at the very front of the frontal lobes. Scientists believe this area of the brain plays a role in the regulation of emotions. Brain imaging techniques show that people who are depressed demonstrate decreased activity in the prefrontal cortex.

Additionally, the ventromedial cortex is a part of the prefrontal cortex that is associated with decision making and mood changes. This area of the brain is typically much smaller in people with depression.

Biology and Depression

Clearly, the relationship between depression and brain activity is far more complex than was once thought. Researchers are continually uncovering new information about the effects of depression on the brain and vice versa. A clear understanding of the biology of depression is critical, as it will facilitate the development of new, more effective treatments for severe depression.


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 Ð aetiology. Retrieved May 5, 2010, from the Lundbeck Institute website:

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

 Posted on : June 26, 2014