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Linking nutrition and the gut microbiota to brain development (2015-12-04)

The human gut contains a microbial community composed of tens of trillions of organisms that normally assemble during the first 2–3 y of postnatal life. Researchers at the Washington University School of Medicine, St. Louis, propose that brain development needs to be viewed in the context of the developmental biology of this “microbial organ” and its capacity to metabolize the various diets we consume.

Scientists hypothesize that the persistent cognitive abnormalities seen in children with undernutrition are related in part to their persistent gut microbiota immaturity and that specific regions of the brain that normally exhibit persistent juvenile (neotenous) patterns of gene expression, including those critically involved in various higher cognitive functions such as the brain’s default mode network, may be particularly vulnerable to the effects of microbiota immaturity in undernourished children.
Furthermore, researchers postulate that understanding the interrelationships between microbiota and brain metabolism in childhood undernutrition could provide insights about responses to injury seen in adults. They discuss approaches that can be used to test these hypotheses, their ramifications for optimizing nutritional recommendations that promote healthy brain development and function, and the potential societal implications of this area of investigation.

In a previous study UCLA researchers have the first evidence that bacteria ingested in food can affect brain function in humans. In an early proof-of-concept study of healthy women, they found that women who regularly consumed beneficial bacteria known as probiotics through yogurt showed altered brain function, both while in a resting state and in response to an emotion-recognition task.

The study, conducted by scientists with the Gail and Gerald Oppenheimer Family Center for Neurobiology of Stress, part of the UCLA Division of Digestive Diseases, and the Ahmanson–Lovelace Brain Mapping Center at UCLA, appears in the online edition of the peer-reviewed journal Gastroenterology.

The small study involved 36 women between the ages of 18 and 55. Researchers divided the women into three groups: one group ate a specific yogurt containing a mix of several probiotics — bacteria thought to have a positive effect on the intestines — twice a day for four weeks; another group consumed a dairy product that looked and tasted like the yogurt but contained no probiotics; and a third group ate no product at all.

Functional magnetic resonance imaging (fMRI) scans conducted both before and after the four-week study period looked at the women's brains in a state of rest and in response to an emotion-recognition task in which they viewed a series of pictures of people with angry or frightened faces and matched them to other faces showing the same emotions.

The researchers found that, compared with the women who didn't consume the probiotic yogurt, those who did showed a decrease in activity in both the insula — which processes and integrates internal body sensations, like those from the gut — and the somatosensory cortex during the emotional reactivity task.

Further, in response to the task, these women had a decrease in the engagement of a widespread network in the brain that includes emotion-, cognition- and sensory-related areas. The women in the other two groups showed a stable or increased activity in this network.

During the resting brain scan, the women consuming probiotics showed greater connectivity between a key brainstem region known as the periaqueductal grey and cognition-associated areas of the prefrontal cortex. The women who ate no product at all, on the other hand, showed greater connectivity of the periaqueductal grey to emotion- and sensation-related regions, while the group consuming the non-probiotic dairy product showed results in between.

The researchers were surprised to find that the brain effects could be seen in many areas, including those involved in sensory processing and not merely those associated with emotion, Tillisch said.

For more information
Feeding the brain and nurturing the mind: Linking nutrition and the gut microbiota to brain development
PNAS 2015 112 (46) 14105-14112

Changing gut bacteria through diet affects brain function, UCLA study shows
UCLA - University of California at Los Angeles