Cortisol is a corticosteroid hormone that is released by your adrenal gland during stressful situations. When the stress does not last very long, the levels of cortisol in your brain dissipate. However, if you are in highly stressful situations, such as war, assault or abuse, then a large amount of cortisol remains in your brain. This can result in adverse effects, such as damage to your hippocampus, an essential part of memory creation.
When you are in a stressful situation, your sympathetic nervous system activates the “fight or flight” response. This is your biological response to stress. Your body shuts down processes such as digestion and increases your heart rate. During fight or flight, the adrenal gland releases cortisol, a corticosteroid hormone. In situations in which your body perceives the stress as a severe threat or the stress is prolonged, an excess level of cortisol becomes active in your brain. Too much cortisol can have negative effects on your hippocampus.
The hippocampus is an essential part of your brain. Located in the medial temporal lobe of your brain, which is above your ears and toward the center of the brain, the hippocampus is responsible for converting short-term memories into long-term memories.
The pivotal neuroscience case of H.M. provided insight into the hippocampus and its functions with memory. H.M. suffered from intractable epilepsy and, in 1953, had his medial temporal lobe removed to reduce symptoms. H.M., however, no longer could create new memories, a condition called anterograde amnesia. Research by many neuroscientists revealed that the hippocampus was responsible for a person's retention of short-term memories and long-term memories.
When an excess amount of cortisol is in your brain, the cortisol affects the function of the hippocampus. As part of fight or flight, blood glucose, which is a source of energy, is diverted from the hippocampus to your muscles. In addition, cortisol interferes with the neurotransmitters' activities, which prevents normal memory function. If the stress is long term, such as with post-traumatic stress disorder, the effects of cortisol on the hippocampus impairs the creation of new memories and the access to existing ones.
- The Franklin Institute, The Human Brain—Stress
- J.D. Bremner, “Does Stress Damage the Brain?”, Biological Psychiatry, 1999