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I’ve got a nice new technique that, to put it simply, uses a sort of drug to target neurons, pump out more receptors and/or transmitters, and alter connectivity among brain cells, allowing the brain’s pathways to be reconfigured and expanded as new paths are created and/or prioritized. By doing this, the drug can insta-teach a very specific set of information (used like “instincts” in the brain—basically “downloading” a stimulus-response action into the user) through the creation of those new particular connections and paths. It’s been carefully designed and refined, at this point literally for centuries or millennia, across many different societies sharing and studying its workings.

So what’s the fastest I could, relatively plausibly, make this drug work on the brain? It needs to be able to rewire the brain to both introduce new information/“instincts”, and to slightly change the way the brain processes input (not breaking or disabling anything outright, but just basically adding an “expansion” and new connections to certain pathways) so that its new information can be processed smoothly by the conscious mind.

In some ways this question could just come down to ”How fast do new synapses/brain pathways form?”, though it’s hard to say exactly how that might be answered since in some ways this drug’s function is like simulating learning (adding new info via new connections) and in other ways it goes deeper (working on a level of subconscious or unconscious instincts, and even of the paths used to simply process perceived sensory input). Not to mention, it does so very actively, promoting much faster creation of receptors/transmitters with the express purpose of quickly shaping particular new connections. Is it possible for me to have this substance’s “rewiring” effect work within seconds to minutes, or is that just too short for the process of brain pathway formation and rewiring, even if mediated by some sort of sci-fi-substance?

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    $\begingroup$ This kind of Q falls into my "how many angels can dance on the head of a pin?" category. Answer: "as many as wanting." We could dredge up all kinds of statistics about learning abilities, but there's so much variation between one person and the next and about informational complexity, talents vs. skills, and so much information that we simply don't know about the brain that the only practical answer you'll get is "whatever number is needed for your story to work well." $\endgroup$
    – JBH
    Jun 28, 2023 at 4:41
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    $\begingroup$ Yes, This is a completely unfeasible technology at the moment, so you can use whatever time frame is most convenient for the narrative. Trying to explain how it works is unnecessary and any explanation is likely to have errors. When worldbuilding sometimes you have to know when its best NOT to give an explanation. $\endgroup$
    – John Smith
    Jun 28, 2023 at 13:39
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    $\begingroup$ The speed of learning is actually the topic of many studies, and there are many known neurological bottlenecks like the thalamus information filter and short term memory chunking limits that are well enough understood to be able to put an approximate speed limit on how fast the brain can learn. While its true that our understanding of the brain is not complete, that is not the same as saying we don't understand it at all. $\endgroup$
    – Nosajimiki
    Jun 28, 2023 at 18:39

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Dream Learning

1: Hacking the brain requires using the brain

The best way to make a believable "brain hack" is to treat it kind of like a computer hack. You can not force the brain (or a computer) to do something that it is not designed to do, but you can hijack the systems that are there to achieve some unintended functionality.

Research shows that the main purpose of dreaming seems to be focused on learning through simulation, making it an ideal brain system to hijack.

According to the field of Behavioral Psychology, thinking is indistinguishable from action when it comes to learning. So, anything you think can be learned, and anything you learn must be thought. That means that if the drug can make you think about and feel all of the memories you want to implant, your memory treats that the same as living through those experiences.

The reason this presents a problem for your drug is that IF you take it while awake, you will start to hallucinate the memories that you are implanting while you try to live your life. This will make focusing on the real world exceptionally difficult during the learning process (Caution: do not operate a motor vehicle while taking this drug). It will also mean that the real world could corrupt your new memories. If you try to do your taxes while experiencing a memory of skydiving, then you may well remember doing your taxes while skydiving. In this way, dream learning lets your brain absorb complex memories without outside interference.

2: Time becomes less of an issue

Dreams happen at the speed of thought; so, they often cover more simulated time than what has actually transpired in real life. People often awaken from dreams that only lasted 15-30 minutes and report having experienced hours or even days in thier dream world. Unhindered by reality, this accelerated "dream time" is probably the limit of how fast the human brain can absorb new experiences.

Part of this is because thought is not limited by the real world so you can actually process the "plot" of a dream faster than you could live it, but part of it is because imagination/memory works by creating memes woven together by logic instead of like a digital video or audio clip where the whole of the experience is recorded. So, part of that acceleration comes from a lack of complete details. The more detailed your dream learning, the longer it will take.

All this said, even though you can live out experiences in accelerated time, a longer memory or set of memories could still take hours of time to record, and it will take a lot of repetition to get most of it since we normally remember less than 10% of what we actually experience.

So, doing it while you sleep may be necessary because you will need relatively long periods of undisturbed brain time to "upload" a memory in any sort of detail.

Some important things to remember about injected memories

Imagine for a second that the following memory is injected into your head.

You stopped for ice-cream in the park and a friendly looking dog stole the ice-cream which made your kid cry. You tried to comfort the kid, but you could not get them to stop crying.

For fun, you might want to write down how you picture it in as much detail as you can before reading the rest of this answer, as this will help illustrate my point later.

The thing about memory not being a video is going to be very important when realizing how different people will absorb implanted memories. No memory is a self-contained event in your brain. Studies into false memories show that everything we remember is interwoven with all of our own personal knowledge and experiences, and that they can actually change each time we replay them in our heads because each replay is actually a new experience. So, if you inject an identical memory into 2 different people's heads, and later ask them to recall it, they will come up with 2 very different narratives of events based on thier own other experiences.

For example, lets say that both Bob and Mary receive the same implanted memory I described above and were asked to recall the memory later, the stories they may tell could sound like this:

BOB: I went to the park with my 2 kids. As we walked along the path near the big white gazebo, we passed under the giant oak tree where the ice-cream guy usually parks his cart. I bought a cookies and cream ice-cream cone to share with the the kids. As we were walking along, a big brown Labrador ran up and snatched the ice-cream right out of my hand! My younger daughter cried so much, I had to carry her the rest of the way home.

MARY: I brought my nephew to the park. There was guy selling ice-cream. I decided to get some for my nephew. As we were walking along, a little beagle came up and stole the ice cream from little tommy's hand. I offered to buy him another one, but he just stood there crying for a long time until eventually I walked him home.

Why are these two memories so different? Because humans make shit up when we remember things. Whenever a memory is incomplete, you inject a bunch of personal biases, assumption, and other memories to create a semi-reliable picture of the event. Even though most of what we remember is made up, it is all based on reasonable assumptions by combining what we know with what we remember to create a usefully completed narrative that is probably true.

Bob and Mary Explained:

Because they remember a kid crying, they both understand that they were there with 1 or more kids, both people impress the most likely candidates into that role. For Bob, it is his 2 kids, because if he went to the park, he knows he'd probably bring both, but for Mary, it was her nephew. She does not have kids, but sometimes she takes him places; so, that makes the most since to her.

Next, is the environment. Bob knows about an ice-cream guy who works in the park; so, he can picture not just that guy, but the whole environment around where he'd expect to run into that guy. In contrast, Mary does not know where she would get ice-cream from in the park; so, she works under the vague assumption that somewhere in this completely un-detailed setting, someone sold her some ice-cream.

Next, each person makes assumptions based on thier own habits. Bob knows that he would normally buy a cookies and cream ice-cream cone to share with the kids. Since he does not remember anything specific about the ice-cream, he assumes this as the default. In contrast, Mary does not normally eat ice-cream; so, she assumes she just bought something for the kid she was with.

Next, assumptions start to compound more as what we've already pictured starts to take hold over what we picture next. For Bob, he remembers sharing the ice-cream, meaning that he must have been holding it, which means the ice-cream had to have been stollen by a big dog to have been able to reach his hand. So, when he pictures a big friendly dog, he imagines a Labrador. But for Mary, she pictures the ice-cream in the child's hand, so if a big dog like a Labrador approached little Tommy, 'friendly' would not be the first thought to pass through her head. So, she instead pictures a smaller friendly dog and comes up with a beagle instead.

Lastly, how each person would comfort the child is different. For starters, Bob has two kids in mind; so, he default picks the one that best fits the story. Bob knows that when his younger daughter cries, his first reaction is to hold her, and if he can't calm her down, he knows he'd just carry her home. But Mary pictures calming down a child as a problem solving exorcise; so, she imagines herself talking to little tommy and trying to offer solutions to the problem.

Because our brains do not record events in full detail, and can not recall events without projecting our own biases onto them, it will be important in your setting to remember that each person's injected memory should be a unique experience, even if it is based off of the same source material.

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There's 2 options here:

1: Matrix esque system - in the scene where Trinity doesn't know how to fly a Helicopter, she calls up link who grabs a minidisk (peak 90s!), inserts it and then uploads it to her. She is competent within a few seconds

However, I get the feeling that's not what you want.

So....

2: The old adage is to master something takes 10,000 repetitions - I'm not sure if there is some study or data to back that up, but let's roll with it for now. In the real world, 10,000 repetitions of anything takes time and has a physical component. Say I want to practice jumping, trying to jump 10,000 times in one go would be exhausting.

However, we are only concerned with the neural pathways, so we just need the brain to run through the process 10,000 times.

Assuming that to run the correct sequence of neurons firing takes a second (Picking this as a number - will expand in a minute) - then 10,000 repetitions is just under 3 hours.

That assumes 100% concentration - however, during this time, the patient still has to live, move etc. so let's say that it's not going at full bore, it's more like using the brains downtime between tasks to run this (like how a computer might have a process that only uses excess processing to run). I think in this scenario, It would be realistic to have the patient gain competency over say an 8 hour sleep cycle.

Now - I said I would get to the 1 second thing later - so here's where you could have some fun. The more complex the task, the longer the 'simulation' in the brain needs to run, for example a simple task like throwing a ball, might take a fraction of a second to run, so it could be learned much quicker. But a skill like juggling (which requires a combination throwing, catching, both hands etc.) might take 2 seconds for the simulation to run, so could take longer. If we expand that to say Room Clearing for a Special forces soldier (where it's multiple complex movements with multiple complex variations) each simulation could take 1-2 minutes, so it would be a matter of 2-3 weeks for it to fully form.

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    $\begingroup$ This is interesting and may be a good basis to start, but I feel like the sort of “learning” it’s focusing on might be a bit different from what I was thinking. The 10,000 repetitions thing seems to be in the context of learning as in mastering a skill (“learning to juggle”, “learning to walk”, etc); I’m thinking of “learning” more generally like the addition of information into the brain (“learning” a fun fact or a new word, or touching a hot stove and learning that doing so hurts—stuff that definitely doesn’t need to be repeated or mastered as a skill) especially since the actual (continued) $\endgroup$
    – inkwell87
    Jun 28, 2023 at 3:30
  • $\begingroup$ “contents” being “put” in the brain by my substance are things that aren’t really learned/mastered like a physical skill or habit is—things like unconscious input-processing pathways, or instinctive stimulus-response actions, the sorts of things lots of animals are born with in some variety or another. Does that sort of distinction make a difference on how this would be done in the brain—since it’s not about mastering a skill or a habit (my characters don’t need to be master pilots/soldiers/ball-throwers instantly), it’s just “adding” information/neuron connections on a more basic level—? $\endgroup$
    – inkwell87
    Jun 28, 2023 at 3:33
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    $\begingroup$ @inkwell87 (a) From the perspective of what we know about how the brain works, learning a skill and "adding information to the brain" is the same thing. There are some people who can glance at a page in a book and recite it for the rest of their lives. There are others who would need to read the page dozens of times and then re-read it at least twice before each recitation. There isn't a single magic number here (the more complex the associations to remember, the more effort is required to permanently store the pattern), and Demon is correct in the analysis. $\endgroup$
    – JBH
    Jun 28, 2023 at 4:38
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Your question made me think of psychedelic therapy, the concept is quite the fad of late. But the matter of the fact is research has shown psychedelics can help in the treatment of psychiatric disorders. We can look at a disorder such as PTSD as the brain having very strong but no longer useful connections that need to be rearranged. Hallucinogens apparently facilitate this un-learning. So why not take them as an inspiration to draw conclusions on how a drug that facilitates learning-learning would work?

In that case, the main take away would be that the speed relies on the dosage but at certain extra high dosage the therapy becomes less controllable and wouldn't be advised. One normal dose already has a decent effect (lets say you learn 70%), but to get to 100% one would have to repeat the sessions again in a couple of weeks. Total session count depends on individual. In the meanwhile, there are people who do not have the time so they risk a higher dose in hopes everything will be done overnight. Rumours says it works for some, others have unexpected consequences.

In other words, we make memories, develop new synapses constantly, it's the guiding them in a specific direction is what's requiring extra time.

My apologies if this is completely different direction than you were looking for, but I hope it is of use nonetheless.

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  • $\begingroup$ The recent Nature article suggests that part of the benefits come from reopening some learning channels and that the learning is dependent on the available teacher / guide. nature.com/articles/s41586-023-06204-3 In other words, the drug alone does not do the trick (as many a drug user can confirm). $\endgroup$
    – David R
    Jun 28, 2023 at 14:07
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This source suggests the human brain can create 1 million synapses every second. This source suggests the brain to have 100 trillion synapses. That gives us a rough rate of change of 0.000001% per second. In other words, it takes 1 million seconds, or 11 days and 14 hours, for the brain to change by 1%. Assuming that learning a skill changes the brain by 0.01%, that gives you a time of about 2 hours and 45 minutes.

Please note that I have no idea what I'm talking about. This answer was created from 5 minutes of googling, some likely mistake-ridden math, and one gigantic assumption. That said, I feel like that amount of time would work well for story purposes.

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Challenges being hand waved:

To get a molecule to not be filtered/ processed by liver/or kidneys is a challenge and different challenge depending on some of the major molecule features.The M, E portion of ADME

Cells are picky about what compounds they let inside.

There is the blood brain barrier. Blocks significant chemical material from crossing. Specifically blocks large molecules.

Most drugs are classified as small molecule which inherently limits amount of information that can be carried.

Every brain is different. Instructions for brain A are almost certainly not going to work for brain B.

By the power of narrative and this lampshade, it is so!.

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