Gut–brain link grabs neuroscientists

Nov 14, 2014

Image: Lester V. Bergman/Corbis

By Sara Reardon

Companies selling ‘probiotic’ foods have long claimed that cultivating the right gut bacteria can benefit mental well-being, but neuroscientists have generally been sceptical. Now there is hard evidence linking conditions such as autism and depression to the gut’s microbial residents, known as the microbiome. And neuroscientists are taking notice — not just of the clinical implications but also of what the link could mean for experimental design.

“The field is going to another level of sophistication,” says Sarkis Mazmanian, a microbiologist at the California Institute of Technology in Pasadena. “Hopefully this will shift this image that there’s too much commercial interest and data from too few labs.”

This year, the US National Institute of Mental Health spent more than US$1 million on a new research programme aimed at the microbiome–brain connection. And on 19 November, neuroscientists will present evidence for the link in a symposium at the annual Society for Neuroscience meeting in Washington DC called ‘Gut Microbes and the Brain: Paradigm Shift in Neuroscience’.

Although correlations have been noted between the composition of the gut microbiome and behavioural conditions, especially autism1, neuroscientists are only now starting to understand how gut bacteria may influence the brain. The immune system almost certainly plays a part, Mazmanian says, as does the vagus nerve, which connects the brain to the digestive tract. Bacterial waste products can also influence the brain — for example, at least two types of intestinal bacterium produce the neurotransmitter γ-aminobutyric acid (GABA)2.


 

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25 comments on “Gut–brain link grabs neuroscientists

  • I imagine the pro-biotic companies are putting this on their websites right now, and carefully eliminating confusing statements like “The evidence that probiotics affect human behaviour is minimal to say the least”, and getting ready to make millions more soon.



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  • 2
    Light Wave says:

    This could be an ‘advert’ disguised as an interesting article….Gut instinct is something I’ve always felt and I listen…I’m also quite picky about what food I eat…..Probiotics wouldn’t be one of them…



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  • My son is ASD (as I now realise after going through the testing process for his ASD that most likely I am also). It has been extremely difficult to get him to eat well as any even mild smell sets him off. This is understandable considering the the fact that brain scans show twice as many synapses in ASD kids and non-ASD. I’d imagine their sensitivities to external stimuli would be explained through massive firing of neurons contiguously. He has as a result a very bland diet which we keep working on, we sneak as much good stuff into stuff he’ll eat but it’s very hard. So it does not surprise me that he would have a very different gut flora than a non-ASD kid. I suspect this may well be a case of confusing correlation with causation.



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  • It trivially easy to experiment with probiotics and decide for yourself if they work. It is not like they are dangerous.

    Personally I am HIGHLY impressed. I am an unusual case, with HIV and really nasty, long standing gut problems.



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  • There have also been studies linking gut microbial population to obesity; certain types of microbes are more prevalent in thin people vs. overweight people. I remember there was some trials going on where the gut microbes of thin people were being transplanted to overweight people; in rats the experiment resulted in the rats losing weight. I wonder if the different microbes influence the appetite and metabolism centers in the brain as well as affecting the absorption of food.



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  • Sue Blue Nov 16, 2014 at 1:50 pm

    I remember there was some trials going on where the gut microbes of thin people were being transplanted to overweight people; in rats the experiment resulted in the rats losing weight. I wonder if the different microbes influence the appetite and metabolism centers in the brain as well as affecting the absorption of food.

    There are probably plenty of opportunities for study, as gut micro-flora is regularly massacred by antibiotics during operations etc.



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  • Reckless,

    It is interesting that ASDs and synaesthesia are strongly correlated. The explosive growth in infant brains (300% from birth to 18 months) results in a huge increase in neuron count and their synaptic connections and the great expansion particularly of the associative cortices. This is then followed by an almost as fierce but exponentially declining rate of pruning away of these random cross couplings.

    It is argued that synaesthesia is the result of this process not going quite to the same level of completion resulting in an overly metaphorical brain. What you describe sounds similar but perhaps associated with still other brain regions.

    Perhaps diet, gut flora and auto-imune processes lie behind this curtailing of the process of apoptosis (pruning the unsed unwanted cross links) resulting in synaesthesia and ASDs? The critical period would be when the bulk of the work is done between 18 months and 4 years, after which key brain functions are fully in place.

    I wonder if uniformity rather than blandness might do the trick for your son? My mother made everything round like crispy fishcakes for me. These could contain a wide variety proteins and veggies but always tasted of cheese as I recall.



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  • Phil and Reckless.
    Your comments are of great interest to me as I researched this area about thirty years ago ….getting my information from books and not the easy access of the internet, unfortunately. At the time the most credible information available to me, was a condition then called Minimal Neurological Impairment or MNI. Today that title seems to have taken on a different meaning and application.

    To my recollection the condition was the result of misplaced messages from the sensory
    organs. The infant’s mind was a jumble of misplaced messages which were very confusing and frightening for the child; hence the over-reaction to loud noises, bright lights, strong smells and tastes. As I recall, it took many years to streamline these messages and put them in their appropriate pigeon-hole in the brain.

    This sounds very similar to the explanation you’ve given Phil. If it’s any consolation to you Reckless, this is a stage that seems to pass though it may require the assistance of an occupational therapist.



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  • This is an important part of autism causes…..I worked with autistic children and they do have gut issues…. It is also said a gluten free and milk free diet can help…..
    But nobody is ever asking why…….??? Why this interaction between different systems in the body??? Neurotoxic elements….ingested, injected or inhaled are often underlined by parents…..but this is a hot and unwanted topic for the medical industry….
    Environmental physicians perfectly know that heavy metals can trigger different neurological issues…with different degrees…linked with gut issues….
    Mercury contained in vaccines for example, ( you will find scandals about MMR vaccines everywhere on the web…), but vaccines are not the only reason….Mercury in dental amalgams can intoxicate the mother, and Mercury is easily circulating through the placenta….
    It is time to have a really scientific approach…by linking all the informations and researches….
    Here is the problem….science and scientific researchers are paid by pharma industries….always to prove we need more drugs and chemicals…
    So gut flora is one part of the explanation….but is not the systemic solution to help or avoid autism



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  • 11
    John Gohde says:

    Eating probiotic’ foods without a doubt would be one of the most indirect ways of improving health imaginable. What is next? Going to see a probiotic witch doctor, no doubt. Reading probiotic research would be incomprehensible, because of all the Latin nomenclature.

    Want to improve your health and diet, then eat a good diet. Enough already with all this probiotic’ foods nonsense.

    autistic children have gut issues

    Really? Then juicing their food would produce faster results.



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  • John Gohde Nov 16, 2014 at 5:34 pm

    Reading probiotic research would be incomprehensible, because of all the Latin nomenclature.

    Unless you actually want to study scientific medicine, bacteriology and the biology of gut microbial populations rather than quackery!

    To study possible effects of neurotoxins, you would also need to read that complex biochemistry stuff and digestion processes!



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  • Roedy Nov 15, 2014 at 8:01 am

    Personally I am HIGHLY impressed. I am an unusual case, with HIV and really nasty, long standing gut problems.

    Summer before last, I had an accident tree felling, and had to have a bowel operation to repair damage.
    The antibiotics massacred my gut flora, so I used some pro-biotics to settle things down until the natural balance had been re-established.



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  • Australia’s premier science TV program Catalyst recently aired a two part documentary on this subject. They are an evidenced based science journalism program similar to the UK Horizon program. They explored this issue in detail. Full technicolour detail. There appears to be good science that variations in gut bacteria result in physical variations in the human. Some good. Some bad. Experiments that change a persons gut bacteria have produced favourable medical results.

    Variations in our diet promote variations in our gut bacteria. They showed experiments where a high level Olympic standard gymnast with a poor diet, was at risk of diabetes because his predominant gut bacteria as a result of his poor diet, was producing huge peaks of sugar. They changed his diet and after 4 weeks, his gut flora had completely changed and his blood sugars had returned to healthy levels. His gymnastic performance also improved.

    Gross out warning. There was a segment in Part Two of the program where people with good gut bacteria would donate faeces that were processed, then injected via an enema into a person who had had there gut bacteria sterilized. Good medical outcomes were being achieved. It made for surreal television. People motivated by honourable intentions, collecting their own fecal material, bagging and tagging it, then delivering it to the medical centre in small plastic bags. Then the lab technician, who’s job (chortle) it was to process these samples and prepare them for the medical injection procedure.

    The programs are too long for me to cite all of the science, but I am a scientific skeptic, and I was impressed by the overall integrity of the program and its exploration of the effects of gut bacteria on humans. Half hour long for each episode. I commend the viewing.

    http://www.abc.net.au/catalyst/stories/4067184.htm



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  • My son is also ASD and particularly regressive when diagnosed at age 4. Now 9 he attends mainstream school in his age group. We have been and continue to be on a remarkable journey as a family. After an intense and fruitless research campaign speaking with a myriad of practitioners we came across GAPS (Gut And Psychology Syndrome). There is a book written by Dr Natasha Campbell-McBride and GAPS consultants across Australia to guide and support (along with an active group of parents). Our son now eats a balanced and healthy diet (as do we). Organic (no pesticides), free-range, sugar-free, un-processed food is key as is fermentation (home made yoghurt & sauerkraut). I highly recommend GAPS as our experience over the past few years has been proof that it works. Once we had his gut healthy, we have been undertaking a neurological therapy for the past 12 months that works on the Vagas nerve amongst other things called HANDLE with again great results. HANDLE is based on a book called The Fabric of Autism by Judith Bluestone. GAPS & HANDLE are our bibles. Our boy has come from aged 4-5 a non-communicator, heading for a “special school” and now well on the path to leading a full and happy life. 🙂



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  • 16
    Observer says:

    Many of the comments here strike me as very funny. Presumably folks on this website have an orientation towards rationality, yet there is this bias to discount anything related to medicine which does not involve some sort of industrial/commercial solution. We humans evolved from slime. While the complexity required to make a human is unimaginable, it happened over billions of years and untold millions of generations. It is then astonishing that something like this should get poo-pooed. I have read there is more non-human DNA in a human than human DNA. It would be more surprising if there was not a huge impact from these other creatures on us- remember our brains which generate our moods, personalities, etc. are a part of the big chemical system that is us. If you want to see what the future will regard as myopic stupidity today, look at the industry funded hacks at http://www.scienceinmedicine.org . Kudos to any scientist that is doing science for the benefit of mankind and not some VCs. There may be some Salks out there yet.



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  • John Gohde Nov 16, 2014 at 5:34 pm

    Want to improve your health and diet, then eat a good diet.

    I would agree, that for healthy people with a balanced gut flora and a good diet, probiotic additives are unnecessary.

    What is next? Going to see a probiotic witch doctor, no doubt.

    This is just silly! Medical advice on digestion is available from doctors who are nutrition specialists.

    Reading probiotic research would be incomprehensible, because of all the Latin nomenclature.

    The inability to read and understand the internationally agreed binomial codes of nomenclature, which are used to to identify and classify, bacteria, fungi, plants and animals, would indicate an inability to identify species and the analysis of properties of these organisms!
    Struggling to accurately NAME the organisms involved, or read the research, is failure at a very superficial level, and hardly a basis for offering advice on the subject!



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  • Observer Nov 16, 2014 at 10:39 pm

    Many of the comments here strike me as very funny. Presumably folks on this website have an orientation towards rationality, yet there is this bias to discount anything related to medicine which does not involve some sort of industrial/commercial solution.

    Looking over the comments, I thought that those discounting the science were a minority.

    It is then astonishing that something like this should get poo-pooed.

    http://www.scientificamerican.com/article/strange-but-true-humans-carry-more-bacterial-cells-than-human-ones/
    All the bacteria living inside you would fill a half-gallon jug; there are 10 times more bacterial cells in your body than human cells, according to Carolyn Bohach, a microbiologist at the University of Idaho (U.I.), along with other estimates from scientific studies. (Despite their vast numbers, bacteria don’t take up that much space because bacteria are far smaller than human cells.) Although that sounds pretty gross, it’s actually a very good thing.

    The infestation begins at birth: Babies ingest mouthfuls of bacteria during birthing and pick up plenty more from their mother’s skin and milk—during breast-feeding, the mammary glands become colonized with bacteria. “Our interaction with our mother is the biggest burst of microbes that we get,”

    I have read there is more non-human DNA in a human than human DNA.

    I think you are talking about shared DNA in various organisms.

    http://genetics.thetech.org/online-exhibits/genes-common
    How much DNA do you share with these living things? Roll the cursor over each image to find out. (See link)



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  • france Nov 16, 2014 at 4:56 pm

    Mercury contained in vaccines for example, ( you will find scandals about MMR vaccines everywhere on the web…),

    Unfortunately just about all of them are anti-vax nonsense!

    but vaccines are not the only reason….Mercury in dental amalgams can intoxicate the mother, and Mercury is easily circulating through the placenta….

    In many areas mercury contamination is widespread in air, in water supplies, and in fish, http://www.nrdc.org/health/effects/mercury/sources.asp – sourced from industry, agricultural run-off, and pollution from burning coal.
    Any tiny quantities of preservative in some vaccines are trivial in comparison to these sources.



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  • The sheer complexity of the cognitions that result from such cross excessive coupling would take a huge amount of brain processing investment to manage. With our neat and tidy cognitions we can easily go “off line” and focus on other things whilst our in-brain modelling system feeds us dummy data and allows us to redirect our attention inwards or very specifically outwards, without feeling we are missing something “out there”. Imagine the huge amount of work our modelling system has to do for such complex, multifacetted cognitions! There may possibly be no modelling respite to allow “going off-line”. No wonder ASDs prefer as little novelty as possible.

    As an aside, I must mention (or re-mention) the great bio-pic about Temple Grandin with Clare Danes as our hero. Just awesome.



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  • Yes, I’ve seen the Temple Grandin film and I’ve seen her interviewed. Great stuff!
    As you no doubt guessed I am the mother of a ‘super sensitive child’ and my line of enquiries was sparked in an effort to find answers. I seemed to be the only person going through this and it made life very difficult.
    Once I had an idea about the problem ,I set to devising a method of treatment off my own bat. Actually, in this case the heightened responses came before the introduction of solid food.
    The condition was quite likely on the AS though I’ll never know for sure. Not all symptoms were present, certainly not the most recognizable feature (difficulty in connecting with others). It’s a vast area so I guess there are many different examples.
    Fortunately the stage passed with time and my next child was more of a daisy than a hot house orchid.



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  • Fortunately the stage passed with time and my next child was more of a daisy than a hot house orchid.

    Good stuff! Both.

    A number of my friends have AS kids of varying severity, but they seem all to be making good progress. I think simply the understanding of the diagnosis (or the acknowledgement of the possibility even) has changed hugely the outcome for kids. Another person of my acquaintance was undoubtedly AS and particularly so as a child before it was recognised for what it is. I think he was certainly set back by a mother who interpreted his behavioural traits as variously naughtiness or stupidity. He suffered greatly as a result.



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  • Even if gut biomes are a mere consequence of diet rather than some kind of independent driver of various effects, including behaviour that influences dietary choices, then at least this biome concept should ensure that 1 or 2 week long dietary experiments which purport to show various effects are rightly regarded as inadequate. From what I understand it can take several months for dietary changes to result in optimal gene expression to suit the altered nutrient profile. That would also presumably apply to the gut biome. Any dietary studies of less than several months duration would therefore be invalid. That probably rules out pretty much all of what is generally accepted nutrition ‘science’.



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