Stress is a common part of modern life, and scientists are beginning to uncover the detrimental effects on the body caused by stress. Research on two key players in the stress response, the amygdala and cortisol, is revealing the crucial role stress plays in regulating hormone levels throughout the brain and body.
Definitions
The amygdala is a multifunctional cluster of neurons that is similar in size and shape to an almond and located in the center of the brain. It is involved in sensory information processing, memory formation, and the stress response. Cortisol is a type of hormone known as a glucocorticoid that is produced by the adrenal glands, which sit atop the kidneys. Two main functions of cortisol are to mobilize energy and suppress the immune system.
Function
The amygdala and cortisol are involved in a complicated network that regulates the stress response, also known as the "fight or flight" response. When a person encounters a fearful, unpleasant or unknown environment, a chain of events in the brain results in a signal to the adrenal glands to secrete cortisol. Cortisol signals the body to release extra energy for fighting or running, and also signals back to regions in the brain, including the amygdala.
Regulation
When cortisol reaches the brain, it sends signals to shut down its own production in a process known as a negative feedback loop. However, cortisol also activates the amygdala, which causes more cortisol to be produced. Other parts of the brain also contribute to this balance of activating and deactivating signals, which ultimately determines when the stress response is shut down and the body resumes normal functioning.
Implications
If the stress response is not turned off, either because the stressful conditions continue or due to hormonal imbalances, the body never returns to its normal resting state. Researchers are beginning to understand that people who continually experience stress exhibit alterations in hormone levels that affect the entire body. This disruption of hormone levels has been linked to depression, osteoporosis and coronary artery disease, according to Dr. Philip W. Gold, chief of the Clinical Neuroendocrinology Branch at the National Institute of Mental Health.
Additional Functions
The amygdala and cortisol are also involved in memory formation. When the amygdala is activated by cortisol, it also interacts with the hippocampus, the region of the brain responsible for creating memories. Scientists think this evolved because particularly stressful situations are those that are worth remembering, Gold explains. For example, if a person steps into the street and almost gets hit by a car, the fear that person experiences triggers the amygdala to signal to the hippocampus to form an intense memory of the event, meaning the person will probably remember to look first next time.
