The Mind-Gut Connection: How the Hidden Conversation Within Our Bodies Impacts Our Mood, Our Choices, and Our Overall Health

by Emeran Mayer

Epige...

overturned dogma in psychiatry.

Studies have shown that when adolescent rhesus monkeys leave their mothers for the first time, they develop separation anxiety and diarrhea—just like many teenagers do when they leave home for college.

In response, fecal bacteria numbers drop significantly, and the ranks of lactobacilli, a genus of protective bacteria,

Pathogenic microbes such as Shigella or E. coli are emboldened,

the investigators confirmed our earlier findings in the same animal model that poor mothering was responsible for the increased responsiveness of the gut to stress, consistent with alterations in the brain’s stress circuits.

newborns of the stressed-out monkey moms had much fewer good gut bacteria—lactobacilli and bifidobacteria—than newborns of monkey moms who’d been left in peace.

stress can alter the mother’s vaginal microbiota, which in turn has a major influence on the newborn’s gut microbes.

the mother’s vaginal microbes first seed the baby’s gut microbiota, these mice gave birth to babies with fewer lactobacilli in their

guts, just as the stressed monkey moms had babies with reduced

lactobacilli in their i...

Many adult brain disorders,

including anxiety, depression, schizophrenia, autism, and most likely IBS,

are now considered neurodevelopmental disorders, meaning that the basic brain changes start very early in life...

maternal gut bacteria—most of them beneficial—have turned up in umbilical cord blood, amniotic fluid, meconium, and on the placenta, according to recent work. As the time of delivery nears, the vaginal microbiota changes a great deal.

During birth, a baby born naturally is exposed to the mother’s vaginal microbiota, including this lactobacillus species, providing the key source of microbes to colonize the infant’s gut.

brain-gut axis had been programmed for life, but the good news is that humans have a very unique part of the brain, the prefrontal cortex, which gives us the ability to override the function of altered brain circuits and learn new behaviors.

These approaches can actually change the wiring of our brains, thereby helping the prefrontal cortex exert some control on an overactive emotional brain network.

This exciting line of research has inspired paradigm-breaking ideas regarding the role of these invisible creatures in our gut reactions and gut feelings, and how they may affect our mood, minds, and thoughts.

These findings suggested that in normal mice, gut microbes produced a steady supply of substances that were able to suppress anxiety, and their effect was transmitted to the brain through the vagus nerve.

Previous studies had shown that certain microorganisms are able to produce the neurotransmitter gamma-aminobutyric acid.

GABA,

broad-spectrum antibiotics reduce the populations of these GABA-producing bacteria, leading to lower GABA levels in the brain and improved brain function.

We know

lactobacilli and the bifidobacteria, have the synthetic machinery to produce GABA.

is it possible that adding an extra supply of these microbes to our diet makes us more relaxed?

Twice a day for four weeks, the active-treatment group ate yogurt enriched with a particular strain of the probiotic Bifidobacterium lactis, along with three other types of bacteria (Streptococcus thermophiles, Lactobacillus bulgaricus, and Lactococcus lactis)

A second group ate a nonfermented milk product that had no probiotics but was indistinguishable in taste, texture, or

appearance from the probiotic-enr...

third group ate no yogurt or mil...

Compared with women who ate the milk product with no probiotics, women who received the probiotic mix for four weeks showed less connectivity between a number of brain regions during the emotion recognition task.

These results showed for the first time that some of the astonishing results from mouse studies apply to humans as well—specifically, that manipulating gut microbiota could measurably change human brain function during a task related to emotions, at least at a very basic emotional reflex level.

But how did the probiotic bacteria from the yogurt communicate with ...

when we analyzed the microbial composition in the stool of study participants, there were no detectable effects of the probiotic ingestion on the types and numbers of the gut microbiota,

However, based on an earlier study, we knew that the identical probiotic treatment can change the metabolites that the gut microbes produce.

It is therefore reasonable to speculate that some of these probiotic-stimulated metabolites reached the brain—either via the bloodstream or in the form of a vagal nerve signal—to change the emotional reactivity of the brain.

However, as subjects showed a reduced responsiveness of emotional brain networks when paying attention to angry, sad, and fearful faces,

we know that certain probiotics are able to dampen emotional reactions to negative contexts.

researchers were able to show that a particular strain of Bifidobacterium reduced experimentally induced depression and anxiety-like behavior in mice as much as the commonly used antidepressant medication Lexapro.

germ-free mice,

After these animals grow up in this sterile world, scientists study their behavior and biology and compare them to genetically identical animals raised under normal conditions.

investigators observed that as adults they overrespond to stressful stimuli by producing more of the

stress hormone corticosterone

When the researchers transplanted beneficial microbiota into these animals’ guts at an early age, they could reverse t...

such a beneficial effect of gut microbial treatment was no longer obse...

adult an...

germ-free mice are less sensitive to pain and less social

biochemical and molecular mechanisms in the brain and in the gut are altered compared with normal mice.

when the germ-free mice were exposed to gut microbiota early in life, they displayed none of these abnormal biochemical abnormalities.

when gut microbiota colonize the gut, it somehow initiates the biochemical signaling mechanisms in the brain that affect emotional behavior.