Gut Bacteria and Memory: Can Manipulating the Former Modulate the Latter?

A friend of mine who is a neurologist recently pointed out to me that while we  are all very familiar with diseases associated with the loss of memory, ie. Alzheimer’s, there are others that are associated with hyper-memory, including PTSD.  In these latter cases, the person continually relives a memory over and over, and cannot stop.  OCD, he explained to me, is another illness of hyper-memory.  You know me:  I brooded (pondered, contemplated, ruminated…dare I say, obsessed?) on this for several days afterwards, and did some outside reading.  Hyperthymesia, which is the name for the anomaly wherein someone has highly superior autobiographical memory (HSAM) – i.e. they can remember an “exceptional number of experiences, and the dates on which they occurred, over many years” – was recently associated with a rare form of OCD.  In a study, 20 people with HSAM had their extraordinary memories tested and the researchers noted a common behavioral pattern:  “…they discovered the participants tended to display obsessive behavior, not unlike people with OCD.” Their conclusion completely confirmed what my friend had told me:  “…their obsessive-compulsive behaviors leads them to constantly reflect on and order memories from their past.”[i]

As you know from my post of a week ago, there are distinct differences in the gut bacteria of those with OCD, according to recent findings.  It was really interesting for me, then to read a recent article on New Atlas about a newly published study showing how the gut bacteria interact with genes to influence memory, as memory seems to closely tied in to OCD behaviors.[ii]  These researchers used a mouse model called the Collaborative Cross, which involves 29 different strains of mice which is used as a model to reflect the genetic variations that occur in human populations.  The scientists discovered that 2 particular sets of genes appeared to be linked to memory in mice.  They then looked at the gut bacteria of the different mouse strains and found that Lactobacillus is the most common family of bacteria associated with better memory – specifically, our old friend, L. reuteri.  That is, L. reuteri seems to improve memory and low levels are linked to poor memory.

I was really surprised.  After all, almost exactly 3 years ago, on May 10, 2017, I wrote about L. reuteri being used to treat PTSD, a hyper-memory disorder.  I described an article in Scientific American where L. reuteri was to be administered to veterans with PTSD in a clinical study.  (I thought the results would have been reported by now, but taking a look at clinicaltrials.gov[iii] shows that the study was only completed a year ago, and apparently, the paper is not yet published.  I’ll continue to watch out for those results.)   That the same bacteria may potentially be used to treat both hyper- and hypo-memory disorders is kind of amazing and very strange.

Back to today’s study:  further experiments done on germ-free mice confirmed that Lactobacillus improved memory.  The researchers could therefore conclude that genes, as well as the composition of the microbiome, independently affect memory.  They believe this has to do with the lactate (lactic acid) produced by Lactobacillus bacteria.  When they gave mice with poor memory lactate, their memories improved.  This has apparently been shown in previous research.  (We know that lactic acid can cross the blood-brain barrier, and that too much of it can cause I kind of intoxication.  Remember my post on that back in August, 2018?  All this shows, yet again,  that too much of something is as bad as not enough…and yes, you can have too much of a good thing…)

The conclusion is that this work needs to be replicated in humans, i.e. that Lactobacillus can improve memory.  As I mentioned above, I’m also still waiting for the results of that study on veterans to be released.  Stay tuned for the exciting conclusions to this exciting biome story!

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[i] https://www.ibtimes.co.uk/hyperthymesia-extreme-memory-skills-linked-rare-form-ocd-1553038

[ii] https://newatlas.com/science/microbiome-gut-bacteria-memory-cognition-lactate/

[iii] https://clinicaltrials.gov/ct2/show/NCT02723344