The Human Microbiome: Guts And Glory


This is MORNING EDITION from NPR News. Good morning, I'm Renee Montagne.


And I'm Steve Inskeep.

Today in Your Health: How the bacteria in your gut may affect your brain. Doctors have long had clues that there may be a connection between what's going on in our heads and what's going on in other parts of our bodies.

MONTAGNE: We all know, for example, that we can get pretty down when we're feeling sick and that our moods lift when we get better. Well, scientists are starting to think about this brain-body connection in a whole new way. And that's because of something we've been hearing a lot about lately: the microbes that live in the human body.

INSKEEP: Turns out you really can have a gut feeling about something, because evidence has been mounting that those microbes in the body may be important for our emotional health as well as our physical health.

NPR's Rob Stein has been exploring the role that our microbes play in our lives in a series of stories over the last few months. And in the final installment, Rob brings us this report about our microbes and our minds.

ROB STEIN, BYLINE: It's early on a Monday morning at the UCLA brain scanning center and Dr. Emeran Mayer is getting ready to peer into someone's brain.

DR. EMERAN MAYER: We're standing in the control room here. The patient is inside the scanning room, not in the scanner itself yet.

STEIN: The patient isn't really a patient at all. She's Pria Tewari, a healthy 29-year-old who volunteered for Mayer's research.

PRIA TEWARI: Growing up in India we believe that what you eat influences your thoughts.

STEIN: So she's here today to help Mayer explore this notion that the microbes that eat what we eat influence our minds.



STEIN: A nurse helps her get into the giant MRI brain scanner.

UNIDENTIFIED WOMAN: OK, Pria, so take a nice deep breath for me, hon. In and out through your mouth.

STEIN: Once she's settled in and the MRI is all set up, the scanning begins.


MAYER: So the first image that was taken, that we just saw on the computer screen, will allow us to extract information regarding, it's what we call the brain signature.

STEIN: A signature of the overall structure of the brain, which Mayer hopes will help answer some provocative questions: Do the trillions of microbes that live in our bodies help mold our brains as we're growing up? Do they continue to influence our moods, behavior and feelings when we're adults? It's something, Mayer says, that has never really been explored before.

MAYER: It really happens rarely in science that you sort of stumble into an area that all of a sudden opens up this completely new frontier.

STEIN: A frontier that could help explain that old idea of gut feelings. And Mayer thinks he already has the first good clues this may be true, after analyzing about 60 volunteers like Pria.

MAYER: We found that the type of community you have, of microbes you have in your gut, is reflected in some ways in some basic architectural aspects of the brain.

STEIN: The brain connections of people whose microbes are dominated by one species of bacteria look different than those of people whose microbes are dominated by another species. That suggests that the specific mix of microbes in our guts helps determine what kinds of brains we have, how our brain circuits develop, how they're wired.

MAYER: The brain circuits obviously determine certain ways of how we perceive the world and react to the world outside of us.

STEIN: This could help explain why some people are born with brains that don't work the way they're supposed to, causing problems like autism, anxiety, depression.

MAYER: It opens up a completely new way of looking at brain function and health and disease. I think that's, you know, kind of a revolutionary concept.

STEIN: So Mayer is scanning hundreds of volunteers like Pria to see if what he's found so far holds up.


STEIN: They move onto the next scan.

UNIDENTIFIED WOMAN: So your instructions for this scan are to close your eyes and rest but don't go to sleep. OK?


STEIN: They want to get a picture of Pria's brain when she's doing absolutely nothing.

UNIDENTIFIED WOMAN: During that scan, did you have any pain or discomfort at all?

TEWARI: No, slight itching there.


STEIN: Now, the obvious question about all this is: How? How could bacteria in our bodies affect our brains? Well, the first clues came from experiments conducted in Europe and Canada.

STEPHEN COLLINS: My name is Stephen Collins. I'm a professor of medicine at McMaster University Medical School in Hamilton, Ontario, Canada.

STEIN: Collins is among the researchers who did these experiments. It's hard to study this stuff in humans. So they used mice. They did things like replace the gut bacteria of anxious mice with bacteria from fearless mice.

COLLINS: And this resulted in a change in behavior. The mice became a little bit less anxious, a little bit more gregarious.

STEIN: It worked the other way around too. The bold mice became timid when they got the microbes of anxious ones. Aggressive mice also calmed down when the scientists altered their microbes by changing their diet, feeding them probiotics, or dosing them with antibiotics.

COLLINS: We saw changes in the brain chemistry in a region called the hippocampus, which is part of the brain that's involved in emotion and mood and so forth, and found that a very important chemical called brain-derived neurotrophic factor was increased.

STEIN: Finally, these scientists figured out how the microbes in the guts of the mice were communicating with their brains - by sending signals up a big nerve known as the vagus nerve.

All this is raising the possibility that scientists could create drugs that mimic these signals. Or just give people the good bacteria - probiotics - to prevent or treat problems involving the brain.

Researchers in Baltimore, for example, are studying one probiotic. Faith Dickerson is a psychologist at the Sheppard Pratt Hospital who is leading that study.

DR. FAITH DICKERSON: The idea is that these probiotic treatments may alter what we call the microbiome and then may contribute to an improvement of psychiatric symptoms.

STEIN: Symptoms like mania in patients suffering from bipolar disorder. Patients like Leah, who ended up being hospitalized after one manic episode. We agreed not to use her full name.

LEAH: I had really bad anxiety and I took Xanax and I took too much Xanax.

STEIN: While she was recovering, Leah heard about the probiotic study and decided to volunteer.

LEAH: It makes perfect sense to me. You know, your brain is just another organ. You know, it's definitely affected by what goes on in the rest of your body.

STEIN: It's too soon to know whether the probiotic being tested in that study is helping. But Leah suspects it might be.

LEAH: It seems like, you know, maybe it helped me because, you know, I'm doing really well and like, I'm about to graduate college and I'm just, you know, doing everything right.

UNIDENTIFIED WOMAN: All righty. So we are going to move on to the final scan, OK?

STEIN: Back at UCLA, Mayer's team is almost done scanning Pria Tewari's brain.


STEIN: While they're finishing up, Mayer explains that he's also been studying the effects of probiotics on the brain. He gave healthy women yogurt containing a probiotic and then scanned their brains, and found subtle signs that the brain circuits involved in anxiety were less reactive.

MAYER: It's the first time that it's been demonstrated in a controlled study that if you alter the gut microorganisms or microbes, that this affects the brain in a fairly profound fashion in healthy people.

STEIN: Mayer says a lot more work will be needed to know whether the probiotic they used in that study - or any probiotics - really can help people feel less anxious.

But Pria Tewari, the volunteer getting scanned today, was in that study too. She thinks maybe, just maybe, she might have noticed something. She was going for her Ph.D. at the time and thought she'd be totally stressed out.

TEWARI: I'd say I definitely, like my anxiety levels were low considering my, my own personal thing that I was going through.

STEIN: It's clear scientists still have a long way to go in all this. But the evidence that's starting to emerge suggests that we probably can't ignore the possibility that our microbes may be affecting our minds.

Rob Stein, NPR News.

INSKEEP: For more about this series including an animation about our friendly microbes - something for your microbes to think about - go to

Copyright © 2013 NPR. All rights reserved. Visit our website terms of use and permissions pages at for further information.

NPR transcripts are created on a rush deadline by a contractor for NPR, and accuracy and availability may vary. This text may not be in its final form and may be updated or revised in the future. Please be aware that the authoritative record of NPR’s programming is the audio.



Please keep your community civil. All comments must follow the Community rules and terms of use, and will be moderated prior to posting. NPR reserves the right to use the comments we receive, in whole or in part, and to use the commenter's name and location, in any medium. See also the Terms of Use, Privacy Policy and Community FAQ.

NPR thanks our sponsors

Become an NPR sponsor

Support comes from