We can classify several different types of scientific truth claims, along with some tips on how to recognize the different types.
Type of truth claim | How to recognize it |
Citation of established fact | Typically occurs with a discussion of the observational facts that proved the claim. |
Citation of a claim that is not yet established fact | Typically occurs with phrases such as “scientists believe” or “it is generally believed” or an appeal to a “scientific consensus.” The claim of a “scientific consensus” is often unfounded, and there may be many scientists who do not accept the claim. |
Citation of a claim that has little basis in observations, and that there may be good reasons for doubting | Often occurs with a phrase such as “it is widely believed,” or maybe a more confident-sounding phrase like “it is becoming increasingly clear” or “there is growing evidence.” |
Claims that memories are stored in synapses fall into the third of these categories. Such claims often are made using the weak-sounding phrase "it is widely believed." To show that, I may cite some of the many times in which writers or scientists suggested that memories are stored in synapses, and merely used the weak phrase "it is widely believed" as their authority.
- "It is widely believed that synaptic plasticity mediates learning and memory" (link).
- "It is widely believed that synapses in the forebrain undergo structural and functional changes, a phenomenon called synaptic plasticity, that underlies learning and memory processes" (link).
- "It is widely believed that synaptic modifications underlie learning and memory" (link).
- "As with other forms of synaptic plasticity, it is widely believed that it [spike-dependent synaptic plasticity] underlies learning and information storage in the brain" (link).
- "It is widely believed that memories are stored as changes in the number and strength of the connections between brain neurons, called synapses" (link).
- "It is widely believed that modifications to synaptic connections – synaptic plasticity – represent a fundamental mechanism for altering network function, giving rise to phenomena collectively referred to as learning and memory" (link).
- "It is widely believed that encoding and storing memories in the brain requires changes in the number, structure, or function of synapses" (link).
- "It is widely believed that long-term changes in the strength of synaptic transmission underlie the formation of memories" (link).
- "It is widely believed that the brain's microcircuitry undergoes structural changes when a new behavior is learned" (link).
- "It is widely believed that long-lasting changes in synaptic function provide the cellular basis for learning and memory in both vertebrates and invertebrates (link).
- "It is widely believed that the brain stores memories as distributed changes in the strength of connections ('synaptic transmission') between neurons" (link).
- "It is widely believed that the long-lasting, activity-dependent changes in synaptic strength, including long-term potentiation and long-term depression, could be the molecular and cellular basis of experience-dependent plasticities, such as learning and memory" (link).
- "It is widely believed that a long-lasting change in synaptic function is the cellular basis of learning and memory" (link).
- "It is widely believed that the modification of these synaptic connections is what constitutes the physiological basis of learning" (link).
- "It is widely believed that memory traces can be stored through synaptic conductance modification" (link).
- "It is widely believed that memories are stored in the synaptic strengths and patterns between neurons" (link).
- "It is widely believed that long-term changes in the strength of synaptic connections underlie learning and memory" (link).
- "It is widely believed that long-term synaptic plasticity plays a critical role in the learning, memory and development of the nervous system" (link).
- "It is widely believed that learning is due, at least in part, to long-lasting modifications of the strengths of synapses in the brain" (link).
- "It is widely believed that long-term memories are stored as changes in the strengths of synaptic connections in the brain" (link).
- "It is widely believed that activity-dependent modification of synapses is the brain's primary mechanism for learning and memory" (link).
- "It is widely believed that synaptic modifications are one of the factors underlying learning and memory" (link).
- "Learning, it is widely believed, is based on changes in the connections between nerve cells" (link).
- "It is widely believed that memories are stored as changes in the number and strength of the connections between brain cells (neurons)" (link).
- "It is widely believed that memories are stored as changes in the strength of synaptic connections between neurons" (link).
- "It is widely believed that memory formation is based on changes in synapses" (link).
These examples by themselves prove that claims of a storage of human memory in synapses are not well-supported scientific claims. People do not tend to use the phrase "it is widely believed" when referring to well-established scientific claims. For example, you never hear someone say "it is widely believed that the sun produces energy through nuclear fusion" or "it is widely believed that people can get diseases from viruses." When you keep hearing people using the weak phrase "it is widely believed," you have a "red flag" sign that you are being referred to a claim that is not very well-supported by evidence.
There is no robust evidence that synapses store human memories. Evidence given to support such claims is merely the kind of evidence we would expect to get, given a large belief community of thousands of richly funded neuroscientists eager to provide evidence for some belief they hold. Similarly, if there was a large well-funded community of thousands of researchers believing that the ghosts of dead animals live in the clouds, such researchers could occasionally produce superficially impressive photos showing cloud shapes that look like animals. Almost invariably, a close examination of papers produced by neuroscientists trying to show evidence for synaptic memory storage will reveal their research was guilty of multiple types of what are Questionable Research Practices. A list of 50 types of Questionable Research Practices is found here. A discussion of some of the misleading tricks used by neuroscientist memory researchers can be found here.
Below I will give ten reasons why there is no credibility in claims that synapses store memories.
Reason #1: One of the main hallmarks of stored information is the use of an alphabet, but there is no sign of any type of alphabet used by synapses.
Although not all types of stored information uses an alphabet, most types of stored information do use an alphabet. Defining the term broadly, we can define an alphabet as a restricted set of symbols used for storing information. One type of alphabet we all know of is the set of characters used in writing a language such as English. To write English sentences, you use a restricted set of 26 letters and a small number of punctuation marks.
There are other types of alphabets. When information is written in binary, we may regard that as using an alphabet consisting of only two symbols: 0 and 1. It is often said that genetic information in DNA is written in an alphabet consisting of only four letters. the chemicals guanine, cytosine, adenine and thymine, Different triple combinations of such chemicals (called codons) stand for different types of amino acids, when such combinations are interpreted using the coding scheme known as the genetic code (depicted below). In the diagram below, A stands for adenine, C stands for cytosine, G stands for guanine, and T stands for thymine.
A requirement for the effective use of an alphabet to store information is what we may sequencing. There must be some physical arrangement that allows for the symbols of the alphabet to appear in a sequence rather than merely in some disordered heap. A book meets such a requirement, by restricting characters to a sequence. DNA meets such a requirement, as it is a chain-like molecule containing long chains of guanine, cytosine, adenine and thymine chemicals in a sequence. A binary file contains such a sequence, as it consists of a sequence of 0's and 1's with a beginning and an end.
There is no sign of any alphabet used by synapses. Synapses have a string-like structure, but there is no sign of any chemicals sequentially stored in such a structure in a way that might be a utilization of an alphabet. Synapses constantly transmit chemical signals passing along them, in a way that results in instability in the chemicals within synapses. Synapses have a presynaptic terminal that is kind of a bag of short-lived chemicals. Such a thing cannot be utilizing an alphabet, because of its disordered structure lacking a sequence.
Reason #2: One of the main hallmarks of stored information is the use of tokens, but there is no sign of any type of tokens used by synapses.
Stored information requires what are called tokens, which can be defined as particular units that represent particular things or ideas or qualities. When stored information uses an alphabet, the tokens are some combination of the symbols of the alphabet, to make a particular word. Stored information that does not use any alphabet can use pictorial tokens to store information.
Let me give an example of how information can be recognized as information even when its meaning has not been deciphered. Imagine someone gives you the image below:
Your second step would be to look for tokens. That could be done by looking for repeated sequences of the characters. A token analysis would show that many of the sequences are repeated. In the visual below, we see some of those repetitions:
Looking in synapses, can we find any tokens? None at all. There is no evidence of an alphabet used by synapses, and there is no evidence of tokens used by synapses.
Reason #3: When stored information does not use either an alphabet or tokens, it will often use pictorial representations; but no such things can be found in synapses.
The discussion above deals mainly with written information such as binary information, textual information or genetic information. But there is another way to produce stored information: by using pictorial representations. A pictorial representation might be a drawing or photo or sketch or video. Is there any evidence that synapses use pictorial representations? None whatsoever. We can imagine no way in which pictures could ever be stored in synapses.
Reason #4: Groups of synapses have no organized arrangement that might enable some information storage.
If there are organized groups of something which seems to have no capability of storing information, there might be some information storage occurring. For example, an individual toothpick seems to have no way of storing information. But if you arrange 100 toothpicks in just the right way, you might store some text. Could it be that information storage arises from some special arrangement of large groups of synapses?
Viewed through electron microscopes, groups of synapses seem to have no organized pattern. If you try to visualize a large vat of spaghetti boiling at the mess hall kitchen of a large army base, you might have a good idea of how disorganized is the arrangement of synapses in the brain. It is therefore not credible to maintain that there is something about the arrangement of synapses that allows them to store information. Returning to the toothpick analogy, we might compare arrangement of synapses in the brain to the disorganized arrangement of a dump truck filled with toothpicks. You can't store information by so disordered an arrangement.
Reason #5: The brain has no synapse pattern reader.
We may further rule out the idea of memories being stored by something in the large scale arrangement of synapses when we consider that the brain has no mechanism for reading the arrangement of synapses in the brain. There are no little eyes floating around in the brain that might allow a brain to retrieve information based on some arrangement of synapses. Nor is there any moving cellular part in the brain that might traverse some arrangement of synapses to figure out what was the particular arrangement of synapses in the brain.
Reason #6: Like muscles in the arm, synapses in the brain do not have some discrete small set of possible strength levels, but have an analog range of strength levels ranging continuously from very weak to very strong.
As the quotes above indicate, it is sometimes suggested that memories are stored by changes of strength levels in synapses. This idea is as nonsensical as claims that your memories can be stored by changes in the strength levels of your arms or legs. One reason that could never work is that the strength levels of your arms and legs do not have a limited set of discrete discontinuous values. Unlike a coin which can only have two discrete states on a table -- a state of "heads" or "tails" -- things such as synapses and arms can have a million different strength levels. You can't store information by variations of an analog continuous variable such as "strength" that can have any number of values, particularly if there's no "strength reader" around to read such a variable.
Reason #7: Chemical synapses (by far the most common type) do not reliably transmit information, so synapses cannot be the explanation for human memory recall which occurs so reliably.
There are two types of synapses: chemical synapses and electrical synapses. The parts of the brain allegedly involved in thought and memory have almost entirely chemical synapses. (The sources here and here and here and here and here refer to electrical synapses as "rare." The neurosurgeon Jeffrey Schweitzer refers here to electrical synapses as "rare." The paper here tells us on page 401 that electrical synapses -- also called gap junctions -- have only "been described very rarely" in the neocortex of the brain. This paper says that electrical synapses are a "small minority of synapses in the brain.")
The predominance of chemical synapses in the brain is a huge problem for all theorists of synaptic memory storage, because of the fact that chemical synapses do not reliably transmit signals. How reliably does a signal travel when it passes between two neurons? It has been repeatedly stated in neuroscience literature that brain signals travel across chemical synapses with a reliability of only .5 or smaller, and almost all synapses in the brain are chemical synapses. In an interview, an expert on neuron noise states the following:
"There is, for example, unreliable synaptic transmission. This is something that an engineer would not normally build into a system. When one neuron is active, and a signal runs down the axon, that signal is not guaranteed to actually reach the next neuron. It makes it across the synapse with a probability like one half, or even less. This introduces a lot of noise into the system."
A scientific paper tells us the same thing. It states, "Several recent studies have documented the unreliability of central nervous system synapses: typically, a postsynaptic response is produced less than half of the time when a presynaptic nerve impulse arrives at a synapse." Another scientific paper says, "In the cortex, individual synapses seem to be extremely unreliable: the probability of transmitter release in response to a single action potential can be as low as 0.1 or lower."
A 2020 paper states this:
"Neurons communicate primarily through chemical synapses, and that communication is critical for proper brain function. However, chemical synaptic transmission appears unreliable: for most synapses, when an action potential arrives at an axon terminal, about half the time, no neurotransmitter is released and so no communication happens... Furthermore, when neurotransmitter is released at an individual synaptic release site, the size of the local postsynaptic membrane conductance change is also variable. Given the importance of synapses, the energetic cost of generating action potentials, and the evolutionary timescales over which the brain has been optimized, the high level of synaptic noise seems surprising."
Faced with such facts, the theorist of synaptic memory storage will try to insinuate that human memory is unreliable, citing a few anecdotes and maybe asking you to recall some embarrassing time you forgot something. But claims that humans cannot remember reliably can very easily be defeated, by citing examples such as these:
- Actors who play Hamlet recall with 100% accuracy more than 1400 lines with complete accuracy.
- Wagnerian tenors who sing the role of Seigfried recall with 100% accuracy not just a comparable number of lines, but also the musical notes corresponding to each of the syllables in the role.
- It is a well established fact that some Muslims can recite with 100% accuracy all the verses in their holy book, a work with more 6000 verses, each consisting of several words.
- Some even more impressive cases of human memory performance are listed in my post here.
Humans can recall things with an accuracy that would never be possible if memory recall required accessing synapses that do not reliably transmit information.
Reason #8: Chemical synapses (by far the most common type) do not transmit information with a speed that can account for instant human memory recall; and no type of synapses have any addresses, indexes or sorting that could explain fast recall.
Besides reliability, a central fact of human memory is speed. Humans routinely recall obscure facts instantly. Any credible theory of memory would have to be one in which memory recall can occur instantly. But we know of an extremely strong reason for thinking that memory recall could never occur instantly if it was occurring by retrieving information stored in synapses. The reason is that traversing synapses would take quite a bit of time. Every jump across the gap of a chemical synapse requires a delay called the synaptic delay. A single synaptic delay is only about 5 milliseconds. But for a signal to travel a decent distance in the brain, there would be very many such synaptic delays. These would add up to a severe slowing factor that would prevent the instantaneous recall that humans routinely experience. We know of things that enable fast retrieval of information in products that human create: things such as addresses, indexing and sorting. No such things exist in synapses or any other structures in the brain. Synapses actually act as kind of neuron anchors that exclude any type of sorting from occurring in the brain (you can't sort something that is anchored to a particular position).
In the paper "Emission of Mitochondrial Biophotons and their Effect on Electrical Activity of Membrane via Microtubules" by 7 scientists, we read this.
"Synaptic transmission and axonal transfer of nerve impulses are too slow to organize coordinated activity in large areas of the central nervous system. Numerous observations confirm this view. The duration of a synaptic transmission is at least 0.5 m/s, thus the transmission across thousands of synapses takes about hundreds or even thousands of milliseconds. The transmission speed of action potentials varies between 0.5 m/s and 120 m/s along an axon. More than 50% of the nerves fibers in the corpus callosum are without myelin, thus their speed is reduced to 0.5 m/s."
The authors then call these "low velocities," and ask how these "low velocities" can explain fast phenomena such as instant recall.
Reason #9: The proteins that make up synapses have short lifetimes of only two weeks or less, causing synapses to be unstable structures unsuitable for explaining memories that can last for 50 years.
Synapses are built from proteins. Research on the lifetime of synapse proteins is found in the June 2018 paper “Local and global influences on protein turnover in neurons and glia.” The paper starts out by noting that one earlier 2010 study found that the average half-life of brain proteins was about 9 days, and that a 2013 study found that the average half-life of brain proteins was about 5 days. The study then notes in Figure 3 that the average half-life of a synapse protein is only about 5 days, and that all of the main types of brain proteins (such as nucleus, mitochondrion, etc.) have half-lives of 15 days or less. The 2018 study here precisely measured the lifetimes of more than 3000 brain proteins from all over the brain, and found not a single one with a lifetime of more than 75 days (figure 2 shows the average protein lifetime was only 11 days).
A ratio every person should remember is that human memories can last for 1000 times longer than the average lifetime of synapse proteins. This is because synapse proteins have average lifetimes of less than two weeks, but humans can reliably remember things for more than 50 years; and 50 years is 1000 times greater than two weeks.
Reason #10: Synapses are connected to other structures in the brain (dendritic spines) known to be unstable short-lived structures, causing synapses to be unstable structures unsuitable for explaining memories that can last for 50 years.
Besides the reason just mentioned, there is a separate reason why synapses are unstable things unsuitable for explaining memories that last for decades: the fact that synapses are typically connected to unstable dendritic spines. Synapses typically 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 2002 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. 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. Speaking of dendritic spines, a 2007 paper says, "Most spines that appear in adult animals are transient, and the addition of stable spines and synapses is rare." A 2016 paper found a dendritic spine turnover rate in the neocortex of 4% every 2 days. A 2018 paper found only about 30% of new and existing dendritic spines in the cortex remaining after 16 days (Figure 4 in the paper).
The Synaptic Memory Claimant Is Like This
Using the term "synaptic memory theorist" is probably too flattering a term to use, because it suggests that people claiming synaptic memory storage actually have a theory. They don't really have any theory at all. All they have is a slogan or sound bite that they keep muttering. When asked about how a brain could store a memory, such people mutter the empty sound bite of "synapse strengthening." If you press for more details, and ask how that could work, all you will get is hand waving.
I can give an analogy for the synaptic memory claimant (a person claiming memories are stored in synapses). He is like an accuser in America who claims that some very old slow-moving widow living in a small cottage is one of the most important spies for the Russians. Let's imagine the old woman's cottage is thoroughly searched by the FBI and CIA, using their most advanced equipment, and no trace of any secret information is found, just as no trace of memories can be found from a microscopic examination of brain tissue, using the most advanced electron microscopes. Suppose observations of the old woman reveal her speech and writing and walking are weak, slow and unreliable, rather like chemical synapses that do not transmit information reliably or very quickly.
We can imagine the desperate attempts the accuser might make to try to keep his story afloat. He might speculate that maybe the dust particles on the woman's floor are using some secret code storing top-secret information. He might claim that the birds chirping on the old woman's roof are specially trained birds which transmit information to hidden nearby Russian microphones. He might claim that maybe when the woman pays for her groceries, she writes secret information in invisible ink on the dollars she gives to the cashier. Making such groundless accusations claiming a woman who bears not the slightest resemblance to a spy is a spy capable of great marvels of espionage, such an accuser would be like the synaptic memory claimant who claims synapses (which bear not the slightest resemblance to a fast-retrieval system for permanently storing information) are the explanation for the astonishing wonders of life-long human memory preservation and instant recall. To such an accuser, we should say: nonsense, nonsense, nonsense, nonsense, NONSENSE. And that is just what we should say to the person claiming that memories are read from synapses: nonsense, nonsense, nonsense, nonsense, NONSENSE.
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