Allergies Stimulate Brain Activity

By Kevin Ritchart

A new study published in the journal Frontiers in Cellular Neuroscience has found that there may be more to the physiology of allergies than typical physical reactions. Allergens can actually have an impact on your brain.

Researchers studied the brains of mice and found that those exposed to a grass pollen allergen produced more neurons than the control group. The study examined the hippocampus, which is the part of the brain responsible for forming new memories and where neurons continue to form throughout life.

Thanks for the Memories

When an allergic reaction occurred, the number of new neurons in the hippocampus increased, which begs the question: what, if any, impact can the consequences of allergies have on memory?

To learn more about the potential impact on memory, researchers are taking a closer look at the immune cells of the brain, known as microglia. Researchers found that the same allergic reaction that triggers the body’s immune system has the opposite effect on the microglia in the brain. 

Rather than being stimulated to act, the resident immune cells in the brain were actually deactivated during an allergic reaction.

“It was highly unexpected to see the deactivation of microglia in the hippocampus...”

"It was highly unexpected to see the deactivation of microglia in the hippocampus," said Barbara Klein, one of the authors of the study. “Partly because other studies have shown the reverse effect on microglia following bacterial infection.

“We know that the response of the immune system in the body is different in case of an allergic reaction versus a bacterial infection. What this tells us is that the effect on the brain depends on the type of immune reaction in the body.” 

A recent World Health Organization report estimated that between 10 and 30 percent of the population suffers from allergic rhinitis, more commonly known as hay fever. So continuing to learn more about the physiology of the immune response to allergens will ultimately benefit a large segment of people around the world.

Making a Connection

Allergic reactions also are responsible for an increase in neurogenesis, or the growth and development of nervous tissue. Thus the question for researchers now becomes whether people who are prone to allergies experience different brain progression than those who are not susceptible.

Further research also aims to solidify the link between advancing age and a reduction in the number and type of neurons produced during an immune response. The type of immune response resulting from the introduction of an allergen is thought to have diverse effects on not just the brain but on the whole central nervous system.

In the future, researchers would like to conduct additional studies to gauge neuron production in the brain throughout the course of a more persistent immune response and further understand the connection between peripheral immune activation and the function of the central nervous system.