Updated: Apr 8
By: Aya Hilal
According to the National Institute of Mental Health, major depressive disorder affects approximately 17.3 million American adults. From a neurological perspective, depression is extremely complex, involving connections between neurons, nerve cell growth, and the levels of certain brain chemicals. Let’s dive into the biochemistry of depression and examine exactly what factors contribute to one of the world’s most common mental illnesses.
When we think of depression and biochemistry, neurotransmitters often come to mind.
Neurotransmitters are chemical messengers in the brain responsible for communication between neurons. Some neurotransmitters that contribute to the development of major depressive disorder include serotonin, norepinephrine, dopamine, and glutamate. Serotonin (5-hydroxytryptamine), often dubbed the “feel-good” chemical, plays a key role in mood, digestion, blood clotting, bone density, and sexual function. Norepinephrine is stored in the neurons of the sympathetic nervous system and is released during times of stress, promoting the “fight or flight” response. Dopamine is a particularly complex brain chemical with diverse influence in emotion, memory, movement, motivation, and reward. Finally, glutamate stimulates the learning process. Typically, low serotonin levels are one of the many biochemical aspects of depression. Many antidepressants target serotonin and norepinephrine jointly, such as Prozac (fluoxetine), which is an SSRI, or selective serotonin reuptake inhibitor. SSRIs generally increase the amount of serotonin available in the brain, thus counteracting the imbalance associated with depression.
In an fMRI study published in The Journal of Neuroscience, it was discovered that the hippocampus is smaller in some depressed people, most likely due to the stress associated with the disorder suppressing neuron production in the brain region. When nerve cell production in any part of the brain is negatively impacted, connections and communication between neurons often suffer. There are many links between depression and mood regulating areas of the brain, such as those in the limbic system. According to Havard Health, the limbic system is a group of structures associated with emotions such as sorrow, fear, pleasure, sexual arousal, and anger. The amygdala, a part of the limbic system, presents an increased amount of activity when a person is clinically depressed. This activity persists after recovery. In addition, the thalamus, another component of the limbic system, is a prime example of depression having an effect upon neuron communication: the thalamus receives an abundance of sensory information that it transfers to the cerebral cortex, which in turn regulates important functions like behavioral reactions and thinking. Issues in the thalamus can lead to depression since the thalamus links sensory input to unpleasant emotions.
The many biochemical factors that play into a person developing major depressive disorder are reflected in its multifaceted symptoms: symptoms of depression include issues with mood, behavior, sleep, weight and cognition. Today, research efforts continue to further examine the body’s most astoundingly complex organ.
Q: What is the function of the thalamus? How can it contribute to an individual experiencing clinical depression?
A: The thalamus receives an abundance of sensory information that it transfers to the cerebral cortex, which in turn regulates important functions like behavioral reactions and thinking. Issues in the thalamus can lead to depression since the thalamus links sensory input to unpleasant emotions.
Q: What is serotonin's role in the body?
A: Serotonin (5-hydroxytryptamine), often dubbed the “feel-good” chemical, plays a key role in mood, digestion, blood clotting, bone density, and sexual function.