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Our future, our universe, and other weighty topics


Sunday, February 11, 2018

Turmoil of the Baffled Engram Theorists

A recent article in Science News was entitled “Somewhere in the Brain Is a Storage Device for Memories.” The article showed how little agreement there is about any theory of how a brain could store memory.

The authors state the following:

Somehow, memories get etched into cells, forming a physical trace that researchers call an “engram.” But the nature of these stable, specific imprints is a mystery.

The claim about engrams is not a statement of scientific fact, but a statement of weakly supported scientific dogma. There still exists no solid proof that any such thing as an engram exists in the human brain.

The article tells us this:

New insights haven’t yet revealed the identity of the physical basis of memory, though. Scientists are chasing a wide range of possibilities. Some ideas are backed by strong evidence; others are still just hunches.

That's pretty much right, except for the part that “some ideas are backed by strong evidence.” There is no theory of physical storage of memory that is backed by strong evidence. Statements such as “insights haven't yet revealed the identity of the physical basis of memory” and “scientists are chasing a wide range of possibilities” are actually indications that there is simply no solid proof for the claim that memories are stored in the brain.

The article says, “One of today’s most entrenched explanations puts engrams squarely within the synapses, connections where chemical and electrical messages move between nerve cells, or neurons.” But the article notes that there are “synapse skeptics” doubting such an explanation, and the article refers to some research challenging this doctrine that memories are stored in synapses. But the article neglects to tell us about what is by far the best reason for doubting this doctrine. It is the fact that human memories can last for 50 years, but synapses are not a suitable place to store memories lasting for years. As discussed here, the proteins that make up synapses are subject to very rapid turnover and replacement, and have an average lifetime of only a few weeks. Even the synapses themselves are subject to turnover, lasting less than a few years.

The article discusses some scientific studies involving optogenetics and memory, and treats the “high hype” press release claims about such studies way too credulously, acting as if such studies provide evidence of some type of cellular storage of memory. They do not do that, because of the reasons discussed here.

The article then quotes a heretical memory storage theory by David Glanzman:


The real engram, he suggests, is the folding pattern of DNA in cells’ nuclei. Changes to how tightly DNA is packed can govern how genes are deployed. Those changes, part of what’s known as the epigenetic code, can be made — and even transferred — by roving RNA molecules, Glanzman argues. He is quick to point out that his idea, memory transfer by RNA, is radical. “I don’t think you could find another card-carrying Ph.D. neuroscientist who believes that.”

Then the article discusses a theory that memories are stored using DNA methylation, and a very different theory that memories are stored in something called perineuronal nets. DNA methylation occurs when a very simple molecule becomes attached to part of a DNA molecule. Such a simple methyl molecule can act like a kind of flag that switches part of a gene on or off. The set of all of these methyl molecules attached to DNA is known as the DNA methylome.

The DNA methylome seems like a fairly stable thing, and so you don't have the “low stability” problem of very rapid protein molecule turnover that you have with the theory that memories are stored in synapses. But there are several reasons why it is not credible to maintain that human memories are being stored in such a DNA methylome.

The first reason is that we already know the function of this DNA methylome, that it is something other than storing memories. The methyl molecules that make up the methylome serve the purpose of genetic expression, a very different task than storing memories. If you were to maintain that the DNA methylome serves both of these purposes, it would be kind of like the Saturday Night Live comedic sketch that described a product like “Miracle Whip.” It went like this:

Wife: New Shimmer is a floor wax!
Husband: No, New Shimmer is a dessert topping!
Wife: It's a floor wax!
Husband: It's a dessert topping!
Wife: It's a floor wax, I'm telling you!
Husband: It's a dessert topping, you cow!
Spokesman: [ enters quickly ] Hey, hey, hey, calm down, you two. New Shimmer is both a floor wax and a dessert topping!

The second reason for doubting that memories are stored in the DNA methylome is that the DNA methylome couldn't be read with the speed needed for memory recall that is very fast. The DNA methylome consists of methyl molecules scattered across a DNA molecule. All evidence suggests that reading DNA is relatively slow. DNA transcription occurs at a rate of about 40 to 80 nucleotides per second, and there are billions of such nucleotides. But think of how fast people can recall memories. On the TV show Jeopardy we see people recalling very obscure memories in only a few seconds. When someone talks rapidly, he is retrieving language memories (such as the memory of what a particular word means) in a fraction of a second. That couldn't happen so fast if some relatively slow process of reading DNA was being used.

The third reason for doubting that memories are stored in the DNA methylome is that the methylome does not grow in size as learning occurs. As discussed here, the DNA methylome is larger (percentage-wise) in a newborn baby than in either a young adult or an old man.

The fourth reason for doubting that memories are stored in the DNA methylome is that methylation suppression experiments do not affect memory very dramatically. Scientists have ways of suppressing DNA methylation, and they have tested the effects of such suppression on learning and memory. A wikipedia.org article says that when DNA methylation is suppressed “recall of existing memories is impaired, but not the formation of new ones.” A scientific paper says that “inhibiting DNA methylation alters olfactory extinction but not acquisition learning.” Another scientific paper says that when DNA methylation was inhibited, “long-term memory strength itself was not affected.” These are not the type of very dramatic effects on learning and memory that one would expect from DNA methylation inhibition if memories were being stored in the methylome.

So since DNA methylation is no better a theory of memory storage than storage of memories in synapses, what is the “really believable” theory of how the brain stores memories? There isn't one. The very claim of the article's title (“Somewhere in the Brain Is a Storage Device for Memories") is itself very dubious (while also being an indication of the lack of a well-established theory). We do not know that brains are storing our long-term memories. The claim that they do is something that has been repeated 10,000 times, but never proven.

As discussed here, the brain seems to have none of the characteristics of physical systems capable of storing information for decades and allowing very rapid retrieval of information. We know from computer systems the kind of things such physical systems have, and the brain doesn't have such things (things such as read-write surfaces allowing permanent storage and very fast retrieval, and indexes and coordinate systems allowing the very rapid retrieval of a specific piece of information from an exact spot).

The term “memory” is perhaps too broad a term, used to describe a learning of body movements, memories of intellectual concepts, and episodic memories of experiences (sometimes called autobiographical memories). It is relatively easy to kind of account for a type of muscle “memory” or body movement “memory” by just imagining a kind of beefing up or strengthening of neurons that were accessed during body movements. But explaining how a brain might store autobiographical memories or conceptual memories seems vastly harder. It is possible that the brain only accounts for muscle memories or body movement memories; and any evidence for such a thing never establishes that a brain is storing autobiographical memories or conceptual memories.

In one of the papers cited by the Science News article, we are told “worms that regenerated from the tails (which lost the original brain) required significantly less training trials to learn ('saving' paradigm) compared to untrained animals.” That's a baffling result inconsistent with claims that memories are stored in brains. Karl Lashley spent many years removing parts of the brains of animals, trying to find some part of the brain that could be identified as the center of memory. He could find no such region. 


We can no more explain memory physically than we can explain consciousness by neurological activity. No one has presented any credible theory of how there could be any neural system that could map all of the types of things that people can remember into any type of molecule that could be used for memory storage. Such a thing would require a wealth of very sophisticated encoding schemes, and there is no evidence that such encoding schemes (which would be a miracle of design if they existed) actually exist.

Let us consider what goes on in a computer with some voice recognition software that stores vocal inputs you speak into a microphone, using a hard disk to write the results. There are three different conversion routines being used. First the sound is converted into a string of alphabetic characters such as d-o-g. Then those characters are converted into decimal numbers using the ASCII system. So that d-o-g is converted to the numbers 100-111-103. Then those decimal numbers are converted into binary numbers, for storage on a disk. 

It seems that a brain would need to be doing many such conversions instantaneously for memory to be written to the brain,  so that some words someone spoke were somehow stored by molecular changes in neurons. But how could that happen, when it seems unthinkable to imagine the idea of such a conversion routine in a brain? No such faculty has ever been discovered, and our minds are terrible at such conversions. Try speaking some words using the simple rule that each letter shall be converted to its ordinal position in the alphabet. That will go at a snail's pace. How could a brain have all these lighting-fast conversion routines when all evidence suggests that minds and brains can't do such work fast? If such lightning-fast conversion algorithms existed in the brain, these elaborate encoding schemes would be miracles of design that would make the problem of explaining human biology much worse.

Then there is the problem of explaining instantaneous memory retrieval, discussed here. I hear the name "John Kennedy" and I instantly recall an image of him and some facts such as the exact date of his death. But if that information was stored on some exact spot of the brain, how could I ever know where that exact spot was, to read that information instantly, when the brain has no coordinate system and no indexing by which some exact  neural location can be specified? A brain is like a vast post office with a million little boxes, and no identifying numbers on any of the boxes -- not an architecture allowing fast retrieval of specific information.

So be suspicious that your mental activity and memory is largely the result of something like a soul, rather than just the by product of neurons.

On page 249 of his book Living in a Mindful Universe, neurosurgeon Eben Alexander says, “The mechanism and location of long-term memory storage remains a complete mystery.” Alexander mentions a reason for doubting that any theory of the brain storage of memories will ever be proven. He states this: “The overall experience of neurosurgeons who have resected large regions of neocortex from every lobe of the brain in countless patients over the last century for myriad pathological conditions...without encountering patterns of broad swaths of memory loss in their patients, belies the notion of the general cortical storage of specific memories as false.” In a similar vein, we read here about how people who have half of their brains removed suffer relatively little loss of memory. How can that be if memories are stored in brains? Near-death experiences give us an additional reason for doubting the brain storage of memories, for in such episodes people often remember things that occurred when their brains were shut down and their hearts stopped.

Let us imagine a planet called Wesoria permanently covered with thick clouds. It might be that no one on such a planet had ever observed the sun providing warmth for the planet. Now, let's consider: how would scientists on this planet account for the warmth of a living organism? They would probably say that the warmth of a body comes purely from chemistry inside the body. But that would be wrong. The warmth of a body on this planet would mainly be coming from an unobserved external heat source – the sun no one on the planet had ever seen.

Scientists on our planet may be comparable to scientists on such a planet. On our planet there is the mystery: what gives rise to the consciousness and mental faculties that we have? Our scientists typically say: it comes purely from our brains. Such a conclusion may be as wrong as the “your body gives you all of your heat” conclusion of the scientists of Wesoria. Our consciousness may be coming from some mysterious external consciousness source, something as unknown and mysterious to us as the unseen sun would be to the scientists of Wesoria. Under such a scenario, it might not at all be true that our long-term memories are stored in our brains.

Postscript:  The 2017 paper here is entitled, "On the research of time past: the hunt for the substrate of memory."  It is a portrait of memory theorists in disarray, presenting no one theory about how memory might be stored in a brain, and instead suggesting seven or more possibilities, none of which is plausible. The paper is all over the map in its speculations, like someone shooting a gun in all different directions. Such theoretical incoherence has no more weight than someone listing 7 possible theories of where angels live. We are told, "Synaptic weight changes can now be excluded as a means of information storage." That shoots down the main theory that neuroscientists have been pushing for decades.  The paper then suggests speculation after speculation, without presenting any evidence for any of these speculations.