Immune Maps in the Brain Create Memory of Past Infections

Implications for Psychosomatic Disorders


Introduction

Jack was severely allergic to pollen from flowers. His friends wanted to play a prank on him and decided to scare him by placing an artificial flower with no pollen in his backpack. As soon as Jack opened his backpack and saw this flower, he started showing symptoms similar to an actual allergic response, and soon developed a full-blown allergic response. Though this story is a figment of the writer’s imagination, this is what happened almost 150 years ago when Mackeszie and researchers studied the effects of an artificial flower on subjects allergic to pollen. This phenomenon is termed as a psychosomatic disorder.

Cleveland Clinic defines psychosomatic disorder as “a psychological condition involving the occurrence of physical symptoms, usually lacking a medical explanation.” This suggests that a disorder may manifest without any apparent physical cause, solely due to “some unknown” effect of the nervous system. While there is no consensus about psychosomatic disorders and its underlying causes, a recently published study by researchers at Technion hints at a possible role of the brain in producing certain immune-related diseases.


The Brain and The Immune System

It has long been recognized that the immune system can affect the functioning of the brain, indirectly through immune mediators, and directly through the actions of immune cells on the nervous system. What this recent study shows is that the converse is true as well. The immune system is directly represented in certain areas of the brain and through these areas, the brain can regulate the immune system.


(scientificamerican.com)


The Study

In the study that was published in a recent issue of Cell, Asya Rolls and her team of researchers from Technion – Israel Institute of Technology used a mouse model to induce inflammation in a part of the gut called the colon. In these mice, inflammation of the colon (colitis) was associated with an increase in the activity of neuronal cells. Specifically, an area of the brain called the insular cortex showed neuronal activation following colitis. This suggested that there was some correlation between colitis and brain activation.


However, the key question was whether the reverse was true? To examine this, researchers artificially activated these same brain neurons in healthy mice. Surprisingly, they found that this led to inflammation that was restricted to the same region of the intestine but not to other areas of the body. This meant that the insular cortex region of the brain had formed a memory of the earlier inflammation and could stimulate the same response in the absence of any pathology in the intestine. Additionally, when these neurons were suppressed, it reduced the inflammation in the colon. So, the key takeaway from this study is that the insular cortex region of the brain can retain information related to immune signaling, similar to the way the brain retains memory. Further studies are essential to elucidate the mechanism involved in this communication between the nervous system and the immune system.


Role of Insular Cortex

The insular cortex region of the brain is also responsible for perception of sensations from inside the body, a process known as interoception. These are largely unconscious perceptions, and include perception of physical sensations in relation to organs such as heart beat, respiration, satiety, etc. It is interesting that the same brain area that is responsible for interoception is also involved in “remembering” the immune response.


Conclusion

This is a very important study which suggests that the brain may be programmed to store information about the immune system, similar to that of the sensory and motor systems. This may have implications for many immune-related disorders such as allergies, ulcerative colitis, Crohn’s disease, autoimmune disease, etc. Better understanding the mechanisms and pathways of neuroimmune signaling may help us manipulate it to manage related disorders.



Written by: Sandeep Pingle, MD PhD