The study, published in Biological Psychiatry​, found that infants with high levels of the bacteria type Bacteroides​ at age one, subsequently performed better in cognitive tests a year later.

"The big story here is that we've got one group of kids with a particular community of bacteria that's performing better on these cognitive tests,"​ commented Rebecca Knickmeyer, PhD, associate professor of psychiatry at the University of North Carolina (UNC).

An additional, unexpected discovery was that infants with highly diverse gut microbiomes performed less well than those with lower bacterial diversity.

"The latter result was quite surprising​," said Knickmeyer. "We had originally predicted that children with highly diverse microbiomes would perform better -- since other studies have shown that low diversity in infancy is associated with negative health outcomes, including type 1 diabetes and asthma.”​

The findings may have big implications for strategies to alter the microbiome to optimise health.

"This is the first time an association between microbial communities and cognitive development has been demonstrated in humans,"​ said Knickmeyer.

Study details​

The UNC researchers collected faecal samples from 89 healthy one-year-olds. They analysed the samples and divided the children into three groups, based on similarities in the make-up of their gut flora.

A year later, the scientists evaluated the children’s performance using the Muller Scales of Early Learning, a collection of tests that examine motor skills, visual reception and language development.

The group with the highest level of Bacteroidetes ​showed the highest overall (Early Learning Composite) scores, while those in the Faecalibacterium ​group scored lowest. However, no group showed signs of impaired learning.

Mechanism undetermined​

The researchers were unable to determine a definitive mechanism underlying the link between microbiome composition and brain development.

However, the findings did raise questions for future research.

“Are the bacteria actually 'communicating' with the developing brain?" ​asks Knickmeyer. "That's something that we are working on now, so we're looking at some signalling pathways that might be involved. Another possibility is that the bacterial community is acting as a proxy for some other process that influences brain development - for example, variation in certain dietary nutrients."​

Although findings are preliminary, the researchers suggest that early intervention may be important to optimising later cognitive development; as increased levels of particular bacteria types appear to be established in the first 12 months of life.

“When measuring the microbiome at age one, we already see the emergence of adult-like gut microbiome communities -- which means that the ideal time for intervention would be before age 1,"​ commented Alexander Carlson, lead author.

Future implications​

The results may facilitate further exploration of links between the infant gut microbiome and aspects of child development such as autism.

"Big picture: these results suggest you may be able to guide the development of the microbiome to optimize cognitive development or reduce the risk for disorders like autism which can include problems with cognition and language,"​ said Knickmeyer. "How you guide that development is an open question because we have to understand what the individual's microbiome is and how to shift it. And this is something the scientific community is just beginning to work on."​

The finding that low microbiome diversity is linked to poor cognitive development also merits further work as it contrasts with previously established associations of high diversity and better physical health. Results from this study support previous research correlating high bacterial diversity with major depressive disorder in adults; – raising the question of whether individual types of gut flora contribute distinctly, but differently, to mental and physical wellbeing.

“Our work suggests that an 'optimal' microbiome for cognitive and psychiatric outcomes may be different than an 'optimal' microbiome for other outcomes," ​speculated Knickmeyer.

Source: Biological Psychiatry​

Published online ahead of print, doi: 10.1016/j.biopsych.2017.06.021​

“Infant Gut Microbiome Associated with Cognitive Development”​

Authors: Alexander L Carlson, Rebecca C. Knickmeyer, et al.​