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Brain Gut Connection

Gut Bacteria and Our Brain – A Developing Connection


Continuing our series on bacteria and its effects on our body, today’s article delves into a developing connection between gut bacteria and our brain. We know it affects our mood and behaviour, but emerging evidence points to the fact that it may be involved in disorders of the brain such as autism, anxiety and depression. This is a plausible connection for two reasons:
bacteria have lived inside humans for millions of years.
our body contains trillions of bacterial cells, weighing between one and three pounds

Our article today uses a recent article from The Atlantic and this was what it had to say about new research and brain disorders:

On Autism:
“Some of the most intriguing work has been done on autism. For decades, doctors, parents, and researchers have noted that about three-quarters of people with autism also have some gastrointestinal abnormality, like digestive issues, food allergies, or gluten sensitivity. This recognition led scientists to examine potential connections between gut microbes and autism; several recent studies have found that autistic people’s microbiome differs significantly from control groups. The California Institute of Technology microbiologist Sarkis Mazmanian has focused on a common species called Bacteroides fragilis, which is seen in smaller quantities in some children with autism. In a paper published two years ago in the journal Cell, Mazmanian and several colleagues fed B. fragilis from humans to mice with symptoms similar to autism. The treatment altered the makeup of the animals’ microbiome, and more importantly, improved their behavior: They became less anxious, communicated more with other mice, and showed less repetitive behavior.”

On Anxiety and Depression:

“Scientists have also gathered evidence that gut bacteria can influence anxiety and depression. Stephen Collins, a gastroenterology researcher at McMaster University in Hamilton, Ontario, has found that strains of two bacteria, lactobacillus and bifidobacterium, reduce anxiety-like behavior in mice (scientists don’t call it “anxiety” because you can’t ask a mouse how it’s feeling). Humans also carry strains of these bacteria in their guts. In one study, he and his colleague collected gut bacteria from a strain of mice prone to anxious behavior, and then transplanted these microbes into another strain inclined to be calm. The result: The tranquil animals appeared to become anxious.

Overall, both of these microbes seem to be major players in the gut-brain axis. John Cryan, a neuroscientist at the University College of Cork in Ireland, has examined the effects of both of them on depression in animals. In a 2010 paperpublished in Neuroscience, he gave mice either bifidobacterium or the antidepressant Lexapro; he then subjected them to a series of stressful situations, including a test which measured how long they continued to swim in a tank of water with no way out. (They were pulled out after a short period of time, before they drowned.) The microbe and the drug were both effective at increasing the animals’ perseverance, and reducing levels of hormones linked to stress. Another experiment, this time using lactobacillus, had similar results. Cryan is launching a study with humans (using measurements other than the forced swim test to gauge subjects’ response).”

On the Connection of Gut Bacteria and Human Brain:

“Perhaps the most well-known human study was done by Mayer, the UCLA researcher. He recruited 25 subjects, all healthy women; for four weeks, 12 of them ate a cup of commercially available yogurt twice a day, while the rest didn’t. Yogurt is a probiotic, meaning it contains live bacteria, in this case strains of four species, bifidobacterium, streptococcus, lactococcus, and lactobacillus. Before and after the study, subjects were given brain scans to gauge their response to a series of images of facial expressions—happiness, sadness, anger, and so on.

To Mayer’s surprise, the results, which were published in 2013 in the journal Gastroenterology, showed significant differences between the two groups; the yogurt eaters reacted more calmly to the images than the control group. “The contrast was clear,” says Mayer. “This was not what we expected, that eating a yogurt twice a day for a few weeks would do something to your brain.” He thinks the bacteria in the yogurt changed the makeup of the subjects’ gut microbes, and that this led to the production of compounds that modified brain chemistry.”

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