Can Bacteria Make You Smarter?

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The potential cognitive gains linked to the role of gastrointestinal bacteria continues to attract international interest. The scientific community are becoming entranced with the notion that our bacterial exposure affects not only the local tissues, but also others including the brain.

Exposure to specific bacteria in the environment, already believed to have antidepressant qualities, could increase learning behaviour.  Mice fed live cultures of Mycobacterium vaccae were able to learn and complete a maze twice as fast as control mice were the key comments delivered at the 110th General Meeting of the American Society for Microbiology last week.

Mycobacterium vaccae is a natural soil bacterium which people likely ingest or breath in when they spend time in nature,” says Dorothy Matthews of The Sage Colleges in Troy, New York, who conducted the research with her colleague Susan Jenks.

The bacteria also changed the mice’s mood – they showed less behaviour that indicates anxiety, such as grooming and searching, perhaps analogous to the calmer behaviour immune activation triggers in people. This is likely to have been caused by changes to the higher mental functions in the forebrain, which perhaps allowed them to focus better on the maze.[1]

One of the questions concerning the use of exogenous bacteria, is does the effect/benefit continue after the supplementation has been stopped. In response to this, the researchers stopped the supplementation and noted that the probiotic mice were less fast than before, but still better than there non supplemented counterparts.

This test was repeated after three weeks and the results were equivocal suggesting that the benefits from supplementation are consistent only whilst being supplemented and for a short period after.


The use of probiotics to effect a change on microbial composition and effect a positive longterm change varies depending on the outcome being sought. The change in neuronal function is likely to be linked to the alteration in concentration of inflammatory cytokines that favour the management of a tolerant or quiet immune system. We keep forgetting in clinical life that a really healthy immune system is doing nothing except observing, it is a loss of this state of tolerance that induces local and systemic health and function changes.

When supplementing a patient with probiotics to achieve a positive change in mental function, the plan must be for long term supplementation, with short periods of recycling, no longer than 21 days apart, based on current understanding. The correct use of specific strains as well as the management of the antibody defences (SIgA) to ensure suitable bacterial information transfer and where required exclusion also represents an important aspect of this approach.


[1] Lowry CA, Hollis JH, de Vries A, Pan B, Brunet LR, Hunt JR, Paton JF, van Kampen E, Knight DM, Evans AK, Rook GA, Lightman SL. Identification of an immune-responsive mesolimbocortical serotonergic system: potential role in regulation of emotional behavior. Neuroscience. 2007 May 11;146(2):756-72. Epub 2007 Mar 23  View Full Paper

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