New Study Hints at Connection Between Microbiome and Behavior

That gastrointestinal issues are comorbid with certain special needs conditions is not news. The seminal study on the brain/gut microbiome connection was performed on mice. Biota-free mice displayed reduced sociability and repetitive grooming. After being “colonized” (meaning having normal mouse biota introduced) the mice displayed fewer abnormal behaviors.1

However, determining if there is a causal link has been difficult. Are the gastrointestinal problems simply a symptom of the underlying condition, or are those gut irregularities being caused by unhealthy microbiota also affecting mood and cognition?

Summarizing the state of the research, a 2014 paper stated, “overall, accumulating evidence in rodent studies suggests that there are links among the microbiota composition, brain bio-chemistry, and behavior.”2

Though the general idea that there are connections between gut microbiota and the brain is becoming widely accepted, we are still a long way from having clear evidence about how and which microorganisms affect mood and behavior. But a short-term study from this year has at least identified one bacterial strain that appears to be worth investigating.

This study, intended as “a prelude to a much larger study,” tracked children for two weeks, taking daily stool samples of a special needs child and that child’s neurotypical sibling. The study intended to correlate behavioral patterns with gastrointestinal status, and “identify organisms of interest for exploration in a larger dataset in the future.”3

The bacterial profiles of the two children were distinctly different. However, the special needs child did not just exhibit low levels of beneficial bacteria, but also had a few strains of bacteria present that had already been observed in other special needs children: Sarcina ventriculi, Barnesiella intestihominis and Clostridium bartlettii.

The real surprise, however, was that during two periods when behavioral issues (including self-harm) manifested, a strain known as Haemophilus parainfluenza made an appearance. The presence of these bacteria in the gut was itself a bit of an oddity. It is a pathogen that is usually found in the respiratory system, often leading to sneezing and coughing. During one of these periods, the child experienced gastrointestinal disturbance, however during the other there were no gastrointestinal problems evident.

For children who have trouble communicating, it can be extremely difficult to determine if negative behavioral changes are attributable to physical discomfort or to some other cause. Studying gut microbiota can, therefore, be particularly murky since the same microorganism that can induce physical pain can also lead to mood and behavioral changes. Put simply, it’s hard to tell if the reason a child is acting out is that their brain chemistry is altered or if it’s that they have a stomachache.  

Since, in this recent study, behavioral changes occurred even when there was no evidence of gastrointestinal distress, the inference that has been drawn is that the behavioral changes were resulting from the bacteria’s influence on the brain, rather than any digestive problems the bacteria may induce.


1. Clarke G, Grenham S, Scully P, Fitzgerald P, Moloney RD, Shanahan F, Dinan TG, Cryan JF (2013) The microbiome-gut-brain axis during early life regulates the hippocampal serotonergic system…Mol Psychiatry 18:666 –673.

2. Mayer E, Knight R, Mazmanian S. Gut microbes and the brain: paradigm shift in neuroscience. The Journal of Neuroscience, November 12, 2014 • 34(46):15490 –15496

3. Luna, RA, Magee, A, Runge, JK, Venkatachalam, M, RubioGonzales, M, Versalovic, J. A case study of the gut microbiome in ASD: correlation of microbial profiles with GI and behavioral Symptoms.

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