How the Body and Brain Respond During Stress
By Christina Radziejewski
What happens to our body when we become stressed? The HPA axis, which consists of the hypothalamus, pituitary gland and adrenal cortex, is activated. When the axis is activated, these three parts of the brain release a series of hormones, resulting finally in the secretion of the stress hormone cortisol.5
The effects of HPA activity allow us to adapt to changes in our internal or external environments.5 Compared to the autonomic nervous system, the HPA axis reacts much more slowly and is more important with longer-term stressors6, such as living in a crime-ridden neighbourhood. In contrast, meeting a knife-wielding mugger in a dark alley is a stressful situation wherein the autonomic nervous system is quickly activated for a fight or flight response.
It is important to note that short term stress can be beneficial, in that it has the effect of inducing the individual to run from the dark alley situation mentioned above, hence removing himself from physical danger. Long term chronic stress, which is the increased and sustained production of cortisol, may cause serious health problems that may not manifest until many years later.
Stress and the Brain
Many studies have been dedicated to the effects of stress on the hippocampus, the part of the brain that is the primary target of stress hormones. The hippocampus is the brain’s main centre for learning and memory. It receives input from other parts of the brain in the formation of declarative memory as well as learning.6,7 Stressful and emotionally-laden events are better recalled by the brain than uneventful ones. This effect is directly attributed to the effect of stress hormones on the hippocampus.6
While stress hormones may be linked to long-term memory retention, prolonged stress can impair memory.8 Prolonged exposure to cortisol as a result of stress has been shown to produce deleterious effects on the brain, such as hippocampal atrophy, or degeneration of the hippocampus.8
Studies have found that older subjects with higher levels of cortisol have reduced hippocampal volume and suffer from greater memory loss, fatigue and depression than those with lower levels of cortisol.7 Diseases that result in severe memory loss such as Alzheimer’s have been directly linked to widespread atrophy in the hippocampus and other brain areas.6,9
In a meta-analysis of 107 studies on chronic stress and its effects on the HPA axis, researchers found that negative effects of stressors depend on the nature of the stressors and vary by the individual’s unique response to them.2 HPA activity depends on the person’s response to stress and increases with subjective stress.2
In other words, while two persons may be subjected to the same stressor, the effects on both can be quite different.