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What Are the Neurophysiological Mechanisms of Depression?

Specific anatomical systems of the body, including the central nervous system (i.e., the brain), peripheral nervous system and endocrine system, can cause and maintain depression. Additionally, certain chemicals---such as neurotransmitters and BDNF---play a critical role in depression.

  1. Limbic System

    • The brain's limbic system, comprising the hypothalamus, amygdala and hippocampus, controls mood, memory and hormone production and influences the emotional and behavioral aspects of depression.

    Hormones and Endocrine System

    • The hypothalamus regulates two glands within the endocrine system, the pituitary gland and adrenal gland. These glands release stress hormones associated with depression, including norepinephrine, cortisol and catecholamines. These hormones influence the sympathetic and parasympathetic branches of the peripheral nervous system.

    Peripheral Nervous System

    • The sympathetic and parasympathetic systems regulate "automatic" physiological functions such as heart rate, breathing rate, blood flow between voluntary and involuntary muscles and so forth. During depression, these systems may become impaired. The physiological result is similar to pressing the gas pedal and the brake at the same time.

    Neurotransmitters

    • Neurotransmitters are the chemical messengers that allow brain cells, called neurons, to communicate with each other. Three neurotransmitters---serotonin, norepinephrine and dopamine---are deployed in the limbic system and are implicated in depression. Antidepressants influence the availability of these neurotransmitters.

    Brain-Derived Neurotropic Factor (BDNF)

    • BDNF is a chemical within the brain that, among other things, enhances the formation of neurotransmitter receptor sites on neurons. BDNF creates more "landing pads" so neurons can better receive neurotransmitter messages from other neurons. Lower levels of BDNF are associated with stress and with depression. Antidepressants appear to work by limiting the effect stress has on decreasing BDNF.

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