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As a Star Trek fan, I’ve been fascinated about the concept of the Borg and how they have used nanotechnology to assimilate every valuable species. They not only incorporate their technology into their own, they use their host bodies to continue to expand their reach throughout the galaxy.

Then I read research about various viruses and bacteria are capable of altering human behavior: Toxoplasma gondii from cat poop has been linked to human anxiety, schizophrenia, and the potential of reducing our sense of danger (there’s a potential link between the parasite and deadly car crashes). Furthermore, the rabies virus alters behavior making animals more aggressive and fearful of water. And then there’s the gut bacteria Acetobacter pomorum, Lactobacillus plantarum, Lactobacillus brevis which have all been linked to making humans crave sugar, and make us more disinclined to eat (or even digest) proteins.

These two concepts got me to thinking about an idea for a bacteria that was capable of fully controlling a human, without the human being aware of it. Effectively the bacteria would control people, sending signals to our brain in order to decide our actions for us. The humans infected wouldn’t even notice, but their friends and family would be able to recognize their behaviors have changed, and their actions may seem strange.

I would like the bacteria to live in the gut in this hypothetical scenario, as there’s a direct link between the gut, which has 500 million neurons in it, and the brain through the vagus nerve and it seems convenient, however I'm looking for any possibilities of overt control. But how possible would something like this be? Is there enough science (even theoretical) to support it, or is there a problem I haven’t thought of that would make this highly unlikely?

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    $\begingroup$ I found an interesting post on Quora by Lois Cronholm, who has a Ph.D. in Biology and Post Doctoral in Microbiology/Immunology, that there are colony bacteria that use quorum by communicating "with chemical signals that create responses that monitor behavior depending on the size and composition of the community". $\endgroup$
    – mkinson
    Commented Nov 9, 2021 at 15:15
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    $\begingroup$ Not an answer, and not a bacteria, but tick tock $\endgroup$
    – Joe Bloggs
    Commented Nov 9, 2021 at 15:17

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Not possible at all.

Imagine a bacteria having access to a random receptor somewhere in the body, lets say a cell that detects heat and sends it to the brain. It doesnt matter what the bacteria does, it cannot send any orders to the brain since any signal will be interpreted as temperature information.

The bacteria would also collectively need to access the information in the brain. They cannot change the hosts actions through nerve input directly if they dont know the situation the host is in. This requires information from the brain to travel to the gut and be accessible for the bacteria. Only the bacteria have access to nerves that send information like tension on the gut to the brain and receive information for muscle movement. They dont have any worthwhile nerves to send and receive actionable intelligence to the brain. And that ignores the fact that the bacteria would have to cooperate to receive, interpret and send the data. A bacteria which receives information has to eventually have a connection to a bacteria that sends information back to the brain, assuming that such nerves somehow exist.

That is a highly complex semi-static structure the bacteria have to build with millions of connections between them to build enough of a system to take control of the human they inhabit. And the worst part is: since they arent a specialized nerve cell designed to think but have to do other tasks to survive as well, they are going to be needing much more biomass to know a tiny bit of the human they inhabit.

Bacteria in the gut dont even use nerves to communicate, but rather use chemicals to reward the host for eating what the bacteria likes.

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  • $\begingroup$ Hypno-toad says: "Ophiocordyceps unilateralis, the zombie-ant fungus, disagrees with you" $\endgroup$
    – PcMan
    Commented Nov 9, 2021 at 13:27
  • $\begingroup$ Rabies lyssavirus agrees with hypno-toad. It may not be a bacteria either but is quite successful in altering its hosts behavior to promote spread of the disease. $\endgroup$
    – PcMan
    Commented Nov 9, 2021 at 13:30
  • $\begingroup$ @PcMan hypno-toad confuses a few set altered behaviours through hormones and selective destruction/alteration of neurons over an extended duration to be the same as an organism capable of selecting a multitude specific actions on the short term for their unwilling host to perform. $\endgroup$
    – Demigan
    Commented Nov 9, 2021 at 13:50
  • $\begingroup$ One can get very complex behavioral changes with very small chemical inputs. Have the bugs secrete some LSD, some Adrenaline or its precursors. Maybe a few milligrams of Testosterone. Presto, you have the Hulk. Add some Ghrelin, and you have Hungry Hulk. Or some Leptin if you want a Hulk-that-ignores-food. LIght-seeking, easy. Light-fearing, easier! The human brain is enormously subject to manipulation by trace chemicals in the bloodstream. If you can combine even the most tenuous direct neural activation with the right chemical trigger, you can control your human like a puppet. $\endgroup$
    – PcMan
    Commented Nov 9, 2021 at 14:10
  • $\begingroup$ @PcMan each is a more long-term change and ignores the "sending signals to their brains to decide our actions for us". Also look at the last paragraph and the idea is to control through neurons, not hormones. $\endgroup$
    – Demigan
    Commented Nov 9, 2021 at 14:14
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A random bacteria can't do it.

You can certainly do a lot with mind control stuff, but there are limits. The bacteria aren't coordinated, each can only act locally, and they're not intelligent enough to coordinate an intelligent response.

They can trigger emotions, or strong urges, but they can't read your mind and model what a brain would do, because they don't have a brain.

It would be even harder from the gut. The gut mostly just controls mood stuff for the brain. It can't stop rational thought.

You need a hive mind bacteria.

A bacteria which as smart as a person could outwit a person. A bacteria which formed some sort of hive mind with connections could embed itself in the gut, form a brain of a similar size to a human, and control the gut.

They wouldn't have absolute control, but they could probably push moods and whims and other things on the person to control them.

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  • $\begingroup$ Gabriel Popkin wrote an article on quantamagazine[dot]org about how Bacteria use brain-like bursts of electricity to communicate with one another in colonies. I found that to be rather interesting, as it suggests that bacteria already exhibits hive mentality. $\endgroup$
    – mkinson
    Commented Nov 9, 2021 at 15:19
  • $\begingroup$ Yeah, you would need ones that were several orders of magnitude better at it than modern ones. $\endgroup$
    – Nepene Nep
    Commented Nov 9, 2021 at 16:52

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