The brain would be able to remember past immune responses and reactivate them to induce a feeling of illness.
- The insular cortex, also known as the insula, is an area of the brain responsible for interoception, i.e. the sense of the physiological state of the body.
- This region is capable of storing immune responses and reactivating them with a simple memory, recreating inflammation.
- These findings open a new therapeutic avenue for treating chronic inflammatory conditions such as Crohn’s disease, psoriasis and other autoimmune diseases by attenuating their memory trace in the brain.
Beyond the physical factor, emotions can play a role in the progression of certain diseases. These are called psychosomatic disorders, where stress or other strong emotions can aggravate symptoms. In a new study, scientists have explored the possibility that the brain itself can trigger symptoms. In work presented November 8 in the journal Cell, Israeli researchers suggest that neurons in the brain are capable of inducing a feeling of illness, or even an actual illness.
Inflammation that recurs without external stimulus
The researchers were particularly interested in the insular cortex, also known as the insula, which is an area of the brain responsible for interoception, or the sense of the body’s physiological state. This includes hunger, thirst, pain and heart rate. They then reasoned that if the body is able to store memories of past immune responses, this brain region must be involved.
To test their hypothesis, the researchers conducted experiments on mice in which they induced inflammation of the colon. Using genetic manipulation techniques, they were able to “capture” groups of neurons in the insular cortex that showed increased activity during inflammation. Once the mice recovered, they artificially triggered these neurons. With no external stimulus other than this triggering of cells in the brain, the inflammation reappeared, in exactly the same area where it was before. The researchers obtained similar results in other mice in which they had induced another inflammatory disease, in this case peritonitis, in the abdominal cavity.
A simple memory triggers inflammation
The mere memory of inflammation is likely to reactivate it.
This is exceptional work, establishing that the classic concept of immunological memory can be represented in neuronsKevin Tracey, a neurosurgeon who was not involved in the study.
The researchers then conducted experiments to test the opposite effect: could removing neurons in mice with active inflammation result in an immediate reduction in inflammation? They found that it did. These results supported the study authors in their hypothesis although this is a basic mouse study and there are multiple challenges in translating the concept to humans. These findings open up a new therapeutic avenue for treating chronic inflammatory conditions such as Crohn’s disease, psoriasis and other autoimmune diseases by attenuating their memory traces in the brain.
Turning this ability to your advantage
While this ability to trigger inflammation may seem negative, it can also be used positively.
There are evolutionary advantages to such a connection,” continues neuroimmunologist Asya Rolls, who led the research group. The body needs to respond as quickly as possible to infection before the attacking bacteria or virus can multiply. […] There is an advantage to being prepared for battle when you are about to face an infection you have already encountered. A shorter response time would allow the body to defeat the infection more quickly and with less effort.