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!
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.
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.
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.
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