RNA memory hypothesis

There’s an old theory that memory is actually encoded in part in RNA. The argument is pretty simple: there’s no obvious way for all that sensory data to be captured in synapses as long term memories, yet long term memories obviously exist and are fairly reliable. RNA, unlike synapses, is energy efficient, redundant and persistent and consistent with what we observe about brains from day to day life.

You’d think with all the neuroscientists running around these days, this would have been eliminated from serious consideration by now, but the opposite is true. There’s actually been a little bit more experimental evidence indicating it might be true. People have allegedly transferred memories between snails, planaria, sea slugs, and there are accounts of people “inheriting” memories after organ transplants. It’s entirely possible that all of these are the result of poor experimental hygiene and wishful thinking, and there’s nothing really there, but they sure are evocative, and it seems like people should be interested in sorting this out, or finding simpler models which have hopes of sorting it out.

I had run across this idea again reading a Ron Maimon screed on physics stack exchange. It’s a pretty good screed worth reading (thanks Laeeth):

Highlight excerpted for the lazy:

RNA ticker tape

It is clear that there is hidden computation internal to the neurons. The source of these computations is almost certainly intracellular RNA, which is the main computational workhorse in the cell.

The RNA in a cell is the only entity which is active and carries significant bit density. It can transform by cutting and splicing, and it can double bind to identify complementary strands. These operations are very sensitive to the precise bit content, and allow rich full computation. The RNA analogous to a microprocessor.

In order to make a decent model for the brain, this RNA must be coupled to neuron level electrochemical computation directly. This requires a model in which RNA directly affects what signals come out of neurons.

I will give a model for this behavior, which is just a guess, but a reasonable one. The model is the ticker-tape. You have RNA attached to the neuron at the axon, which is read out base by base. Every time you hit a C, you fire the neuron. The recieving dendrite then writes out RNA constantly, and writes out a T every time it recieves a signal. The RNA is then read out by complementary binding at the ticker tape, and the RNA computes the rest of the thing intracellularly. If the neuron identifies the signal recieved RNA, it takes another strand of RNA and puts it on the membrane, and reads this one to give the output.

The amount of memory in the brain is then the number of bits in the RNA involved, which is about a gigabyte per cell. There are hundreds of billions of cells in the brain, which translates to hundreds of billions of gigabytes. The efficiency of memory retrieval and modification is a few ATP’s per bit, with thousands of ATP’s used for long-range neural communication only.

The brain then becomes an internet of independent computers, each neuron itself being a sizable computer itself.

 

This is a pretty exciting idea, and there are several near relatives. There are protein kinases involved in mRNA transcription and immunology which are candidates for memory as well. Functionally they’re all kind of similar: the idea is the long term memory is chemical and exists on the sub cellular level. 

Mechanisms are known to exist. If RNA is the persistence substrate, you’d expect there to be something like a nucleotide gated channel in the brain, so it can talk to the signal processing components of the brain. There is, starting from the olfactory system, which is known to be associated with memory. Such RNA gated channels are also important in the hippocampus; the master organ of memory in the brain.  Furthermore, it’s entirely possible that the glial cells have something to do with it; the function of these are still poorly understood. Women have more of them than men; maybe that’s why they can always remember where your keys are. There’s plenty of non-protein transcripting RNA floating around in the brain doing …. stuff, and nobody really knows what it does.

One of the cute things about it, is it is entirely possible RNA works like some kind of ticker tape for a Turing machine the way Maimon suggests above. There are a number of speculations to this effect. One can construct something that looks like logic gates or a lambda calculus through RNA editing rules; various enzymes we know about already more or less do this; weirder stuff like methylation may also play a role.

There are obvious ways of figuring all this out; people do look at RNA activities in the hippocampus for example. But because this theory is out of fashion, they attribute the activity to things other than direct RNA memory formation. Everyone more or less seems to believe in the Hebbian connectome model, despite there being little real evidence for it being the long term memory mechanism, or much understanding of what brains do at all beyond relatively simple image recognition/signal processing type stuff it is known to do. Memory is much more mysterious; seemingly a huge reservoir of super efficient data-storage.

The fact that more primitive organisms which are completely without nervous systems seem to have some kind of behavioral memory system ought to indicate there is something more than Hebbian memory. People are starting to notice. You have little single-cell critters like paramecia responding to stimuli, and acting more or less in as complex a way as larger organisms which do have some primitive nervous system. Various “microtubule” theories do not explain this (sorry Sir Roger), as disrupting them doesn’t change behavior much.

One can measure memory in some of these little beasts; the e. coli that lives in your bowels and in overhopped beers have a memory of at least 4 seconds; better than some instagram influencers. Paramecia have memories which may last their entire lifetime -if the memories are transferable via asexual reproduction (not clear they are; worth checking) that would be a couple of weeks: vastly better than most MSNBC viewers. Larger unicellular organisms like the 2mm long stentor exhibit very complex behaviors. They behave much like multicellular animals they more or less compete with. No neurons! Lots of behavior. Levels of behavior which would be very difficult to reproduce even using the latest megawatt dweeb learning atrocity that would otherwise be used to (badly) identify cat videos.

Since humans evolved from unicellular life, there should be some more primitive processing power still around, very possibly networked  and working in concert together. We already know that bacterial colonies kind of do this; even using similar electrical mechanisms to what is observed in brains. It’s completely bonkers to me that modern “neuroscientists” would abandon the idea of RNA memory when …. something is going on with small unicellular creatures. There is obviously some mechanism for the complex behaviors exhibited by unicellular life, and RNA is weird and active enough, it is a plausible mechanism. Maybe they’re not aware of this because unicellular organisms don’t have neurons? Argument for them taking a more comprehensive biology course, or, like, looking at something other than neurons through a microscope if so.

I’m not sure hyperacuity is fully understood. I’ve read things which claim that dolphin, electric eel, bat and human hyperacuity (eyeballs, or fast reflexes in video games) is  a sort of interferometry done with the rate encoding of the spikes of nervous impulses. It’s possible that this is true, but it is also possible that some extra, offloaded computational element governs this amazing phenomenon. To put a few numbers on it: bat nervous systems can echolocate on a 10 nanosecond time scale, electric eels 100nanoseconds. Biological nervous systems operate on a rate encoded sort of sub kilohertz time scale, but resolve things on a gigahertz time scale; that’s a pretty remarkable characteristic. They claim the neurons are doing some fancy interferometry on the rate encoded spikes that nervous systems are known to operate on, but there is much hand waving going on. I’ll wave my hands further and wonder if offloading some of the computation on RNA computers on the cellular level might help somehow. Certainly neural nets with memory layers are vastly more powerful than those without. Granted the thing on your video card isn’t very Hebbian either, but one can make the argument at least on the box diagram signal processing level.

There are fascinating consequences to this, I think some of which were explored by 50s and 60s science fiction authors who were aware of the then popular RNA memory hypothesis. Imagine you could learn a new language by taking an injection. Of course if such a technology were possible, absolutely horrific things are also possible, and, in fact, likely, as early technological innovations come from large, powerful institutions. 

There are various mystics who assert that humans have multiple levels of consciousness. Gurdjieff, the rug-merchant and mountebank who brought us the phrases “working on yourself” and … “consciousness,” asserted that the average human consciousness was a bunch of disconnected automatons that could occasionally could be unified into a whole, powerful being. While I think Gurdjieff mostly seemed interested in fleecing and pantsing the early 20th century equivalent of quartz-crystal clutching yoga instructors, his idea is one of the few usefully predictive hypothesis for why stuff like hypnosis and advertising (marketing hypnosis) works. Maybe he stumbled upon the multicore networked RNA memory hypothesis by accident. Maybe the ancients are right and the soul resides somewhere in the liver. Don’t laugh; people have led normal lives with giant pieces of their brain removed, but nobody has survived the death of their livers. The former fact; normal people getting by without much brain tissue, at least, ought to be the end of the argument: purely Hebbian models of the brain are obviously false.

Debate in the literature:

https://www.frontiersin.org/articles/10.3389/fnsys.2016.00088/full

https://www.frontiersin.org/articles/10.3389/fnsys.2018.00052/full