Neurologists
like to assume that all your memories are stored in your brain. But
there are actually quite a few reasons for doubting this unproven
assumption, including the research of scientists such as Karl Lashley
and John Lorber. Their research showed that minds can be
astonishing functional even when large parts of the brain are
destroyed, either through disease or deliberate surgical removal.
Lorber documented 600 cases of people with heavy brain damage (mostly
due to hydraencephaly), and found that half of them had above average
intelligence. Some children with brain problems sometimes undergo an
operation called a hemispherectomy, in which half of their brain is
removed. An
article in Scientific American tells us, “Unbelievably, the surgery
has no apparent effect on personality or memory.” In Figure 1 of
this paper, we see a brain X-ray of a person with very little brain
tissue, who is described as "normal." Apparently he got
along fairly well with very little brain.
Given
such very astonishing anomalies, we should give serious consideration
to all arguments against the claim that your brain is storing all
your memories. In my previous two posts, I presented two such
arguments. One argument was based on the apparent impossibility of
there naturally developing all of the many encoding
protocols the brain would need to store the many different things humans
store as memories. The second argument I gave was based on the
apparent impossibility of explaining how the human brain could ever
be able to instantly recall memories, if memories are stored in
particular locations in the brain, because there would be no way for
the brain to figure out where in the brain a memory was stored.
In
this post I will give a third argument against the claim that your
brain stores all your memories. The argument can be summarized as
follows: there is no plausible mechanism by which the human brain
could store very long-term memories such as 50-year-old memories.
Every neurological memory theory that we have cannot explain any
memories that have persisted for more than a year.
The
Fact That Humans Can Remember Things for 50 Years
First,
let's look at the basic fact of extreme long-term memory storage. It
is a fact that humans can recall memories from 50 years ago. Some
people have tried to suggest that perhaps human memory doesn't work
for such a long time, and that remembering very old memories can be
explained by the idea of what is called “rehearsal.” The idea is
that perhaps a 60-year-old remembering is really just remembering
previous recollections that he had at an earlier age. So perhaps,
this idea goes, when you are 60 you are just remembering what you
remembered from your childhood at 50, and that at 50 you were just
remembered what you remembered from your childhood at age 40, and so
forth.
But
such an idea has been disproved by experiments. A scientific study
by Bahrick showed that “large portions of the originally acquired
information remain accessible for over 50 years in spite of the fact
the information is not used or rehearsed.” The same researcher
tested a large number of subjects to find out how well they could
recall the faces of high school classmates, and found very
substantial recall even with a group that had graduated 47 years ago.
Bahrick reported the following:
Subjects
are able to identify about 90% of the names and faces of the names of
their classes at graduation. The visual information is retained
virtually unimpaired for at least 35 years...Free-recall probability
does not diminish over 50 yr for names of
classmates assigned to one or more of the Relationship Categories A
through F.
I
know for a fact that memories can persist for 50 years, without
rehearsal. Recently I was trying to recall all kinds of details from
my childhood, and recalled the names of persons I hadn't thought
about for decades, as well as a Christmas incident I hadn't thought
of for 50 years (I confirmed my recollection by asking my older
brother about it). Digging through my memories, I was able to recall
the colors (gold and purple) of a gym uniform I wore, something I
haven't thought about (nor seen in a photograph) for some 47 years.
Upon looking through a list of old children shows from the 1960's, I
saw the title “Lippy the Lion and Hardy Har Har,” which ran from
1962 to 1963 (and was not syndicated in repeats, to the best of my
knowledge). I then immediately sung part of the melody of the very
catchy theme song, which I hadn't heard in 53 years. I then looked up
a clip on a youtube.com, and verified that my recall was exactly
correct. This proves that a 53-year-old memory can be instantly
recalled.
So
in trying to explain human memory, we need to have a theory that can
explain human memories that persist for 50 years. Very confusingly,
scientists use the term “long-term memory” for any memory lasting
longer than an hour, which is very unfortunate because almost every
thing you will find on the internet (seaching for “long term
memory”) does not actually explain very long-term memory such as
memories lasting for 50 years.
Why
LTP and Synapse Plasticity Cannot Explain Very Long-Term Memory
Now
let's look at neuroscientists' theories of memories. Quora.com is a
“expert answer” website which claims to give “the best answer
to any question.” One of its web pages asks the question, “How
are memories stored and retrieved in the human brain?” The top
answer (the one with most upvotes) is by Paul King, a computational
neuroscientist. King very dogmatically gives
us the following answer:
At
the most basic level, memories are stored as microscopic chemical
changes at the connection points between neurons in the brain..As
information flows through the neural circuits and networks of the
brain, the activity of the neurons causes the connection points to
become stronger or weaker in response. The strengthening and
weakening of the synapses (synaptic plasticity) is how the brain
stores information. This mechanism behind this is called "long-term
potentiation" or "LTP."
But there is
actually no proof that any information is being stored when synapses
are strengthened. From the mere fact that synapses may be
strengthened when learning occurs, we are not entitled to deduce that
information is being stored in synapses, for we also see blood
vessels in the leg strengthen after repeated exercise, and that does
not involve information storage. In order to actually prove that a
synapse is storing information, you would need to do an experiment
such as having one scientist store a symbol in an animal's brain (by
training), and then have another scientist (unaware of what symbol
had been stored) read that symbol from some synapses in the animal's
brain, correctly identifying the symbol. No such experiment has ever
been done.
The evidence does
not even clearly indicate that LTP correlates with memory, as the following
scientist's summary of experimental results indicates (a summary
utterly inconsistent with the claim LTP is a general mechanism to
explain memory).
What
this means is that LTP and memory have been dissociated from each
other in almost every conceivable fashion. LTP can be decreased and
memory enhanced. Hippocampus-dependent memory deficits can occur with
no discernable effect on LTP...There
will be no direct quantitative or even qualitative relationship
between LTP measured experimentally and memory measured
experimentally—that is already abundantly clear from the available
literature...The
most damning observations probably are those examples where LTP is
completely lost and there is no effect on hippocampus-dependent
memory formation.
A scientific paper
states this about LTP:
Based
on the data reviewed here, it does not appear that the
induction of LTP is a necessary or sufficient condition for the
storage of new memories.
What is misleadingly
called “long-term potentiation” or LTP is a not-very-long-lasting
effect by which certain types of high-frequency stimulation (such as
stimulation by electrodes) produces an increase in synaptic
strength. Synapses are gaps between nerve cells, gaps which
neurotransmitters can jump over. The evidence that LTP even occurs
when people remember things is not very strong, and in 1999 a
scientist stated (after decades of research on LTP) the following:
[Scientists] have
never been able to see it and actually correlate it with learning and
memory. In other words, they've never been able to train an animal,
look inside the brain, and see evidence that LTP occurred.
Since then a few
studies have claimed to find evidence that LTP occurred during
learning. But there is actually an insuperable problem in the idea
that long-term potentiation could explain very long-term memories. The
problem is that so-called long-term potentiation is actually a very
short-term phenomenon. Speaking of long-term potentiation
(LTP), and using the term “decays to baseline levels” (which
means “disappears”), a scientific paper says the following:
Potentiation
almost always decays to baseline levels within a week. These results
suggest that while LTP is long-lasting, it does not correspond to the
time course of a typical long-term memory. It is recognized that many
memories do not last a life-time, but taking this point into
consideration, we would then have to propose that LTP is only
involved in the storage of short-term to intermediate memories.
Again, we would be at a loss for a brain mechanism for the storage of
a long-term memory.
A
more recent scientific paper (published in 2013) says something
similar, although it tells us even more strongly that so-called
long-term potentiation (LTP) is really a very short-term
affair. For it tells us that “in general LTP decays back to
baseline within a few hours.” “Decays back to baseline” means
the same as “vanishes.”
Another 2013 paper
agrees that so-called long-term potentiation is really very
short-lived:
LTP
always decays and usually does so rapidly. Its rate of
decay is measured in hours or days (for review, see Abraham 2003).
Even with extended “training,” a decay to baseline levels is
observed within days to a week.
So evidently
long-term potentiation cannot be any foundation or mechanism for
long-term memories. This is the conclusion reached by the previous
paper when it makes this conclusion about long-term potentiation
(LTP):
In
summary, if synaptic LTP is the mechanism of associative learning—and
more generally,
of memory—then it is disappointing that its properties explain
neither the basic properties of associative learning nor the
essential property of a memory mechanism. This dual failure contrasts
instructively with the success of the hypothesis that DNA is the
physical realization of the gene.
But what about
syntaptic plasticity, previously mentioned in my quote from the
neurologist King? Since he claimed that LTP is the mechanism
behind synaptic plasticity, and LTP cannot explain any memory lasting
longer than a year, then synaptic plasticity will not work to explain
very long-term memories.
Why
Synapses Cannot Explain Very Long-Term Memory
Long-term memory
cannot be stored in synapses, because synapses don't last long
enough. Below is a quote from a scientific paper:
A
quantitative value has been attached to the synaptic turnover
rate by Stettler et al (2006), who examined the appearance and
disappearance of axonal boutons in the intact visual cortex in
monkeys.. and found the turnover rate to be 7% per week which would
give the average synapse a lifetime of a little over 3 months.
You can read Stettler's paper here.
You
can google for “synaptic turnover rate” for more information. We
cannot believe that synapses can store-long memories for 50 years if
synapses only have an average lifetime of about 3 months. The paper here says the half-life of synapses is "from days to months."
Synapses often protrude out of bump-like structures on dendrites called dendritic spines. But those spines have lifetimes of less than 2 years. Dendritic spines last no more than about a month in the hippocampus, and less than two years in the cortex. This study found that dendritic spines in the hippocampus last for only about 30 days. This study found that dendritic spines in the hippocampus have a turnover of about 40% each 4 days. This study found that a subgroup of dendritic spines in the cortex of mice brains (the more long-lasting subgroup) have a half-life of only 120 days. The wikipedia article on dendritic spines says, "Spine number is very variable and spines come and go; in a matter of hours, 10-20% of spines can spontaneously appear or disappear on the pyramidal cells of the cerebral cortex." A paper on dendritic spines in the neocortex says, "Spines that appear and persist are rare." While a 2009 paper tried to insinuate a link between dendritic spines and memory, its data showed how unstable dendritic spines are. Speaking of dendritic spines in the cortex, the paper found that "most daily formed spines have an average lifetime of ~1.5 days and a small fraction have an average lifetime of ~1–2 months," and told us that the fraction of dendritic spines lasting for more than a year was less than 1 percent. A 2018 paper has a graph showing a 5-day "survival fraction" of only about 30% for dendritic spines in the cortex. A 2014 paper found that only 3% of new spines in the cortex persist for more than 22 days.
Furthermore, it is known that the proteins existing between the two knobs of the synapse (the very proteins involved in synapse strengthening) are very short-lived, having average lifetimes of no more than a few days. A graduate student studying memory states it like this:
Synapses often protrude out of bump-like structures on dendrites called dendritic spines. But those spines have lifetimes of less than 2 years. Dendritic spines last no more than about a month in the hippocampus, and less than two years in the cortex. This study found that dendritic spines in the hippocampus last for only about 30 days. This study found that dendritic spines in the hippocampus have a turnover of about 40% each 4 days. This study found that a subgroup of dendritic spines in the cortex of mice brains (the more long-lasting subgroup) have a half-life of only 120 days. The wikipedia article on dendritic spines says, "Spine number is very variable and spines come and go; in a matter of hours, 10-20% of spines can spontaneously appear or disappear on the pyramidal cells of the cerebral cortex." A paper on dendritic spines in the neocortex says, "Spines that appear and persist are rare." While a 2009 paper tried to insinuate a link between dendritic spines and memory, its data showed how unstable dendritic spines are. Speaking of dendritic spines in the cortex, the paper found that "most daily formed spines have an average lifetime of ~1.5 days and a small fraction have an average lifetime of ~1–2 months," and told us that the fraction of dendritic spines lasting for more than a year was less than 1 percent. A 2018 paper has a graph showing a 5-day "survival fraction" of only about 30% for dendritic spines in the cortex. A 2014 paper found that only 3% of new spines in the cortex persist for more than 22 days.
Furthermore, it is known that the proteins existing between the two knobs of the synapse (the very proteins involved in synapse strengthening) are very short-lived, having average lifetimes of no more than a few days. A graduate student studying memory states it like this:
It’s
long been thought that memories are maintained by the strengthening
of synapses, but we know that the proteins involved in that
strengthening are very unstable. They turn over on the scale of hours
to, at most, a few days.
A
scientific paper states the same thing:
Experience-dependent
behavioral memories can last a lifetime, whereas even a long-lived
protein or mRNA molecule has a half-life of around 24 hrs. Thus, the
constituent molecules that subserve the maintenance of a memory will
have completely turned over, i.e. have been broken down and
resynthesized, over the course of about 1 week.
The
paper cited above also states this (page 6):
The
mutually opposing effects of LTP and LTD further add to the eventual
disappearance of the memory maintained in the form of synaptic
strengths. Successive events of LTP and LTD, occurring in diverse and
unrelated contexts, counteract and overwrite each other and will, as
time goes by, tend to obliterate old patterns of synaptic weights,
covering them with layers of new ones. Once again, we are led to the
conclusion that the pattern of synaptic strengths cannot be relied
upon to preserve, for instance, childhood memories.
When
you think about synapses, visualize the edge of a seashore. Just as
writing in the sand is a completely unstable way to store
information, long-term information cannot be held in synapses. The
proteins in between the synapses are turning over very rapidly
(lasting no longer than about a week), and the entire synapse is
replaced every few months.
In
November 2014 UCLA professor David Glanzman and his colleagues
published a scientific paper publishing research results. The authors said, “These results challenge the idea that stable synapses store
long-term memories." Scientific American published an
article on this research, an article entitled, “Memories May Not
Live in Neuron's Synapses.” Glanzman
stated, “Long-term memory is not stored at the synapse,” thereby
contradicting decades of statements by neuroscientists who have
dogmatically made unwarranted claims that long-term memory is stored
in synapses.
Why
Very Long-Term Memories Cannot Be Stored in the Cell Nucleus
His
research has led Glanzman to a radical new idea: that memories are
not stored in synapses, but in the nerve cell nucleus. In fact, in
this TED talk Glanzman dogmatically declares this doctrine. At 15:34
in the talk, Glanzman says, “memories are stored in the cell
nucleus – it is stored as changes in chromatin.” This is not at
all what neurologists have been telling us for the past 20 years, and
few other neuroscientists have supported such an idea.
We should be extremely suspicious and skeptical whenever scientists suddenly start giving some new answer to a fundamental answer, an answer completely different from the answer they have been dogmatically declaring for years. For example, if scientists were to suddenly start telling us that galaxies are not hold together by gravity (as they've been telling us for decades), but by, say, “dark energy pulsations,” we should be extremely skeptical that the new explanation is correct. In this case, there are very good reasons why Glanzman's recently-hatched answer to where long-term memories are stored cannot be right.
Chromatin
is a term meaning DNA and surrounding histone protein molecules.
Histone molecules are not suitable for storing very long-term memories
because they are too short-lived. A scientific paper tells us that the half-life of
histones in the brain is only about 223 days, meaning that every 223
days half of the histone molecules will be replaced.
So histone molecules
are not a stable platform for storing very long-term memories. But what
about DNA? The DNA molecule is stable. But there are several reasons
why your DNA molecules cannot be storing your memories. The first
reason is that your DNA molecules are already used for another
purpose – the storing of genetic information used in making
proteins. DNA molecules are like a book that already has its pages
printed, not a book with empty pages that you can fill. The second
reason is that DNA molecules use a bare bones “amino acid”
language quite unsuitable for writing all the different types of
human memories. The idea that somewhere your DNA has memory of your
childhood summer vacations (expressed in an amino-acid language) is
laughable.
The third reason is
that the DNA of humans has been exhaustively analyzed by various
multi-year projects such as the Human Genome Project and the ENCODE
project, as well as various companies that specialize in personal
analysis of the DNA of individual humans. Despite all of this huge
investigation and analysis, no one has found any trace whatsoever of
any type of real human memory (long-term or short-term) being stored
in DNA. If you do a Google search for “can DNA store memories,”
you will see various articles (most of them loosely-worded,
speculative and exaggerating) that discuss various genetic effects
(such as gene expression) that are not the same as an actual storage
of a human memory. Such articles are typically written by people
using the word “memories” in a very loose sense, not actually
referring to memories in the precise sense of a recollection.
The fourth reason is
that there is no known bodily mechanism by which lots of new
information can be written to the storage area inside a DNA molecule.
The fifth reason is that the DNA we see in brain neurons is basically identical to the DNA we see in other parts of the body (such as the DNA from foot cells). If memories were stored in DNA, the DNA in brain neurons would be much different from that of the DNA in other body parts.
The fifth reason is that the DNA we see in brain neurons is basically identical to the DNA we see in other parts of the body (such as the DNA from foot cells). If memories were stored in DNA, the DNA in brain neurons would be much different from that of the DNA in other body parts.
To completely defeat
the idea that your memories may be stored in your DNA, I will merely
remind the reader that DNA molecules are not read by brains – they
are read by cells. It takes about 1 minute for a cell to read only
the small part of the DNA needed to make a single protein (and DNA
has recipes for thousands of proteins). If your memories were stored
in DNA, it would take you hours to remember things that you can
actually recall instantly. Thinking that DNA can store memories is
like thinking that your refrigerator can cook a steak.
But couldn't
very-long term memories just be stored in some unknown part of a
neuron? No, because the proteins that make up neurons have short
lifetimes. A scientist explains the timescales:
It is occasionally speculated that long-term memories might be stored in microtubules in a cell. But such things do not last long enough to be a storage place for memories lasting decades. A scientific paper tells us how short-lived brain microtubules are:
Neurons possess more stable microtubules compared to other cell types (Okabe and Hirokawa, 1988; Seitz-Tutter et al., 1988; Stepanova et al., 2003). These stable microtubules have half-lives of several hours and co-exist with dynamic microtubules with half-lives of several minutes.
When It Comes to
Explaining Very Long-Term Memory, Our Neuroscientists Are in Disarray
So how can we
summarize the current state of scientific thought on how long-term
memory is stored? The word that comes to mind is: disarray.
In this matter our scientists are flailing about, wobbling this way
and that way; but they aren't getting anywhere in terms of presenting
a plausible answer as to how very long-term memory can be stored in the
brain. Our scientists have done nothing to plausibly solve the
permanence problem – the problem that very long-term memories cannot be
explained by evoking transient “shifting sands” mechanisms such
as LTP which last much less than a year (or in neurons, which are
rebuilt every two months due to protein turnover). On this matter
our scientists have merely presented explanatory facades – theories
that do not hold up to scrutiny, like some movie studio building
facade that you can see is a fake when you walk around and look
behind it, finding no rooms behind the front.
Another sign of this disarray is a 2013 scientific paper with the title, “"Very long-term memories may be stored in the pattern of holes in the perineuronal net." After basically explaining in its first paragraph why current theories of long-term memories do not work and are not plausible, the author goes on to suggest a wildly imaginative and absurdly ornate speculation that perhaps the brain is a kind of a giant 3D punchcard, storing information like data used to be stored on the old 2D punchcards used by IBM electronic machinery in the 1970's. The author provides no good evidence for this wacky speculation, mainly discussing imaginary experiments that would lend support to it. The very appearance of such a paper is another sign that currently scientists have no good explanation for very long-term memory. I may note that IBM punchcards only worked because they were read by IBM punchcard-reader machines. In order for the brain to work as giant 3D punchcard, we would have to imagine a brain-reader machine that is nowhere to be found in the human body. There has never existed such a thing as a punchcard that can read itself.
Often
the modern neuroscientist will engage in pretentious talk which makes
it sound as if there is some understanding of how very long-term
memory storage can occur. But just occasionally we will get a little
candor from our neuroscientists, such as when neuroscientist Sakina
Palida admitted in 2015, “Up to this point, we
still don’t understand how we maintain memories in our brains for
up to our entire lifetimes.”
Conclusion
For the reasons
given above, there is no plausible mechanism by which brains such as
ours could be storing memories lasting longer than a year. There are
only a few possible physical candidates for things that might store
very long-term memory in our brain, and as we have seen, none of them are
plausible candidates for a storage of very long-term memory.
So given this
explanatory failure and the proven fact that human memories last 50
times longer than a year (a period of 50 years), we must reject neural
reductionism, the idea that human mental experiences can be fully
explained by the brain. We must postulate that very long-term memory
involves some mysterious reality that transcends the human brain –
presumably some soul reality or spiritual reality. The reasons for
this rejection include not just the matter discussed in this post,
but the equally weighty reasons given in my two previous posts: the
fact that the storage of all memories in the human brain would
involve insuperable encoding problems (as discussed here), and the
“instant retrieval” problem (discussed here) that there is no way to explain how your
brain could know where to find a particular stored memory if the
memory was stored in your brain.
The fact that our
neurologists claim to have theories as to how very long-term memories
could be stored does not mean that any such theory is tenable.
Imagine if you lived on a planet in which your consciousness and
long-term memory was due to a soul, and that the first time
scientists dissected a brain, they found that the brain was filled
with sawdust. No doubt such scientists would get busy inventing
clever theories purporting to explain how sawdust can generate
consciousness and long-term memories.
I may note that
memories stretching back 50 years are inexplicable not merely from a
neurological standpoint but also from a Darwinian standpoint. As I
will argue in another post, from the standpoint of survival of the
fittest and natural selection, there is no reason why any primate
organism should ever need to remember anything for longer than about
a year or two (it would work just fine to just keep remembering last year's memories). I may note that according to an article on wikipedia.com, the
average life span in the Bronze Age was only 26 years old. There is
no reason why natural selection (prior to the Bronze Age) would have
equipped us to remember things for a length of time twice the average
life span in the Bronze Age, and it is not plausible that very
long-term memories are a recent evolutionary development.
Some objections can
be made against my claim that very long-term memories cannot be
stored in the brain. One such objection involves the fact of memory
impairment in Alzheimer's disease and stroke. This objection is very
easily answered, and I will do so in my next post.
Postscript: I forgot to mention capacity considerations that give another reason for ruling out DNA as a storage place for human memory. It has been estimated that 1 gigabyte of memory (1000 megabytes) can store about 3000 books. The entire storage capacity of a DNA molecule is only about 750 megabytes. But the memory savant Kim Peek was able to remember the entire contents of 10,000 books (in addition to countless other things). Even if we assume 250 megabytes of free storage available in a DNA molecule, it wouldn't be a tenth of what is needed to store human memories, and would probably be less than a hundredth.
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