What goes on in the head is influenced by the body’s defenses. It can help memory, but it can also make you scary.
The brain and the immune system are not only the most complex parts of the body, they both also have something special, a memory. This is ensured by the adaptive branch in the immune system, it consists for example of T cells that are unspecialized (“naive”) and after their first encounter with something foreign, such as a bacterium, memorize its biosignatures and keep them ready for later encounters. The brain remembers very differently – by strengthening the connections between cells, it is still not well understood – and the brain is also different in many other ways than the rest of the body, it is isolated from it and “immune tolerant”, has a weaker immune system – with other immune cells: microglia – and it can afford it because it is difficult for something to penetrate the brain, the blood-brain barrier takes care of that. So is the drawn parallel between the two memories something entirely external?
No, the brain and the immune system communicate with each other, but it was ignored for a long time because both are complicated enough. Then the brain initially showed influences on the immune system: In the event of prolonged stress, it dampens the activity of the immune system with its stress hormones – glucocorticoids – that seems absurd, but the brain needs as much energy as possible for itself during stress. For example, a simple cold can spread through the body, and the defense must be patient until an important test is over, then the fever comes, often at the start of vacation, many have had this experience.
–
