When we perceive a situation to be threatening, our adrenal glands produce stress hormones to prepare us to deal with the threat. This is the ‘Fight, flight or freeze’ response, which works wonderfully well to get us out of acute danger. Things go awry when we are faced with a situation that we perceive as stressful, but that we feel we cannot leave, such as a high-pressured job or a difficult relationship. In such situations, stress hormones, particularly cortisol, are constantly secreted.
Continuously elevated cortisol levels lead to a number of health problems, such as elevated blood sugar levels, raised insulin levels, abdominal weight gain and high blood pressure.
Cortisol also interferes with memory formation. The part of the brain involved in new memory formation, the hippocampus, is saturated with receptors for cortisol and very sensitive to sustained cortisol levels. In fact, long-term stress causes damage to neurons in the hippocampus, leading to shrinkage of this important area.
Stress also interferes with sleep. How often have you woken at two or three o’clock and lain awake for a few hours worrying? This is usually due to raised cortisol levels. Normally, cortisol levels fall toward the evening and remain low during the night. This allows levels of another hormone, melatonin, to rise, ensuring a good night’s sleep. Stress disrupts this normal pattern, keeping cortisol levels elevated at night and disrupting sleep.
Normal sleep rhythm, with alternating periods of deep sleep and REM sleep, is necessary for the formation and consolidation of new memories. If this rhythm is disturbed, consolidation of memories cannot take place. In addition, the hippocampus controls your circadian rhythm, or sleep-wake cycle. Stress-induced damage to the hippocampus disrupts this cycle, leading to disordered sleep patterns, further compounding the problem. Lack of sleep also decreases focus and attention, making it more difficult to remember important facts in the first place.
Decreasing stress levels is thus of utmost importance in improving our ability to remember, and protecting our precious brain from the ravaging effects of sustained cortisol elevation. Yoga, Tai Chi and meditation all have proven benefit here. Exposure to nature and gentle exercise both decrease cortisol levels. The development of psychological tools such as mindfulness allows us to deal better with stressful situations.