> I STRONGLY believe there is a substantial central nervous system microbiome, but (spoiler alert) no evidence found in that search :)
What gave you reason to believe this if you found no evidence of it in your own search?
What gave you reason to believe this if you found no evidence of it in your own search?
We're lucky to live in a scientific era during which a "gut microbiome" is taken for granted (heck, even FDA-approved treatments depend on it! Google FMT, but don't click "images" from your work laptop), but it wasn't so long ago that we felt microbes were unlikely to live endogenously and harmlessly anywhere in the body.
There were also some hypotheses (untested, if memory serves) that COVID-19 influenced olfactory neurons through direct infection. Don't tell the blood-brain barrier, but if I were a bacterium, the nasal palate would be my ingress strategy. Or maybe the gums or gut — one of the cranial nerves, certainly. [edit] I should clarify — covid is viral, not bacterial, but it does show that this is a potential entry vector.
The central nervous system is incredibly complicated, and our symbiotic relationship with microbes is extraordinary. I think it does a disservice to bacteria to suppose they DON'T get involved in an organ :)
[1] https://www.space.com/ryugu-asteroid-sample-earth-life-colon...
The inner of the two Muc2 mucin-dependent mucus layers in colon is devoid of bacteria https://pubmed.ncbi.nlm.nih.gov/18806221/
Bacteria penetrate the normally impenetrable inner colon mucus layer in both murine colitis models and patients with ulcerative colitis https://gut.bmj.com/content/63/2/281
So I think without trillions of bacteria to exclude, in the absence of any other issues excluding bacteria from the brain seems pretty doable.
Many viruses infect neurons, but they are way smaller than bacteria.
That is, we believe, very strongly, that it's impossible for two masses to repel each other gravitationally, for example, but we will never have actual proof it's impossible.
None of this to say that it's irrational to believe in a brain microbiome despite this search seeming fruitless, as there are good a priori arguments for expecting one to exist.
Exactly. Like the apocryphal small chocolate teapot orbiting the Earth
For the last 400 years, pathologists on every country had filleted and put, lets say tens thousands of human brains and human guts under the microscope. One of them has systematically a microbiome, easy to see. The other don't, except when is diseased or rotten. The sample token here is huge, maybe millions.
If we would had searched 400 years for this chocolate teapot without finding it, we could conclude with a solid suspicion that there is not such thing.
This is very different than just saying "I don't think that there is bacteria in the brain but I never searched for it". All pathology science is based in searching for it. We created gram staining dyes, scanners, tags, gold coated plates for electronic microscopes, DNA analysis... exactly for that.
If there really is a microbiome living in each healthy brain, we should have found it 150 years ago.
Is that really the case? By my understanding of the article, we find plenty of bacteria whenever we look at human brain samples. The problem is that it's very hard to tell if that bacteria was already present in the brain, or if it got in through the process of cutting the brain open (especially by contamination with other tissues), or if it was indeed present before the procedure, but only because the individual was very old or had a disease.
The chocolate teapot example is a non sequiter as it fails both Occam’s razor and the principle that extraordinary claims require extraordinary evidence not to mention that it wouldn’t follow any laws of known science and it’s existence very well would upend quite a few of those. The scientific method isn’t something you get to apply piecemeal.
If I said "I STRONGLY believe that a teapot is out there," it would be reasonable to ask me why.
Evidence is a thing that you claim could be part of an valid argument that something happened ("is consistent with"). This isn't a universal definition, but there's got to be some separation between proof and evidence. When there's evidence admitted into a court case, it doesn't necessarily mean that someone is guilty. When there's a lot of evidence and still no proof, you can and should (and will) still make a probabilistic case that something did happen.
So I'd agree with and disagree with you. There's no evidence (that you know of) that Russell's Teapot is there, which is why you do not believe it is there. If somebody does believe it is there, but admits that they have no proof that it is there, it would be reasonable to ask what evidence makes them believe that it is there.
Where I obviously agree with is that "belief" can't mean just something you want to think for no particular reason. Or if it does, it's certainly not worth talking about.