So the title might boggle you, because you did not come across that specific terminology in the text. But in fact it is just another synonym we did visit in the text: psychoneuroimmunology. I was interested in this topic because it explains a relationship between the immune system (yes) and the central nervous system. Yes, in fact, chemicals involved in fighting infection can be linked to emotional feelings like depression and other mental mechanisms.
To illustrate, first I must introduce what is called the HPA axis which stands for the hypothalamus-pituitary-adrenal cortex.
The image below depicts what happens when a stimulus of stress is introduced via externally (i.e., you experience through your sense of sight, smell, touch, etc.). It leads to a cascade of responses that involves the HPA axis. First response, through the hypothalamus, which releases CRF and so on....
Stress is a broad term. It can change its meaning and purpose if you place "stress" in a different context. Like in psychology, when we mention stress, we immediately associate it with emotions, like frustration or anger. However, in physical biology, stress means an injury. A physical trauma to the foot or finger or what have you. And the immune system is directly involved in eradicating stress to the physical aspect of your body. Levels of white blood cells (WBCs) that fight infection, such as cytokines and natural killer cells, are elevated in response to a physical stress like a cut in your bleeding finger, etc. But it has been shown that elevated levels of cytokines, are also correlated with emotional stress. One explanation is that (as shown in the table below) increased cortisol production directs its energy to increasing metabolism and therefore detracts energy synthesizing proteins. In other words, increasing the cortisol production will lead into a deprivation of normal levels of B cells, T cells, and natural killer cells, which are all WBCs found in the immune system. Having low levels of WBCs mean depression and extreme sadness.
Prolonged stress also harms the physiological aspect of the brain. In the hippocampus elevated levels of cortisol can mean toxicity that eventually leads to damage in the neurons of the hippocampus, which is responsible for maintaing stability in emotional pursuits.
It’s interesting how stress not only can be an emotional state but can also cause injury. When I think of stress I think about frustration, anger, worriedness that I have throughout my life. The hippocampus liked you mention in your blog, does play a huge role in our brain. Not only, if damaged can cause stress like you explained, it may also lead to depression as well. Our brain works in mysterious ways, ways that we as society are still learning about each and every day.
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