The human body, though a miraculous machine, is also a sort of mobile terrarium for other living things. In fact, 99% of the genes in your body aren’t yours – they belong to bacteria, viruses, fungi and other microorganisms. These microorganisms live almost everywhere—in the mouth, eyes, nasal passages, genitals and on the skin—but mostly, they’re in your gut.
The gut microbiome includes hundreds of species of bacteria, comprising 100 trillion cells—more than exist in a human body. Yet until very recently, the idea that these microorganisms could influence human health and behavior was soundly rejected.
Over the past decade, however, the gut biome has gained some respect. It’s now recognized as an important part of human health and function, with effects implicated in a variety of conditions, from the obvious (inflammatory bowel disease) to the not-so-obvious (Parkinson’s disease). Neurodevelopmental and mental disorders (such as autism and depression) have been studied most extensively. Neurological disorders, such as stroke and epilepsy, have remained scarcely examined, although interest has been growing.
The gut-brain axis
Given the blood-brain barrier, the idea that bacteria in the gut could influence the brain was even harder to swallow. But an increasing number of studies are finding intimate communication between the gut and brain, as well as complex interplay among the gut microbiome, the brain and the rest of the body.
Given their range of effects on the body and their constant interactions with the nervous system, gut microbiota are now thought to play a role in many neurological disorders. For example, giving antibiotics to mice prone to Alzheimer’s disease — in order to destroy most of the gut bacteria—reduced the number of clumped proteins in the brain that have been linked with dementia. A later study gave young mice antibiotics for only a week; as they grew, their brains showed less evidence of Alzheimer’s.
Do they play a role in epilepsy? Can gut microbiota affect seizure frequency? Can certain populations of bacteria predispose to seizures, and can we harness the power of the microbiome to stop seizures?