New Poll Suggests About 29% of Neuroscientists Doubt the Synaptic Memory Theory

 Although it is often claimed that memories are stored in the brain (specifically in synapses), there is no place in the brain that is a plausible storage site for human memories that can last for 50 years or longer. The proteins that make up both synapses and dendritic spines are quite short-lived, being subject to very high molecular turnover which gives them an average lifetime of only a few weeks 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).  

Both synapses and dendritic spines are a “shifting sands” substrate absolutely unsuitable for storing memories that last reliably for decades. Synapses are connected to dendritic spines, which have short lifetimes. 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). 

So it should be doubly-clear that synapses cannot store memories that can last for decades. Similarly there are two reasons why information would not last long if written on maple leaves outdoors: (1) the fact that maple leaves decay after a few months, and (2) the fact that the wind tends to blow away leaves lying outdoors. 

If humans were storing their memories in brains, there would have to be a fantastically complex translation system (almost infinitely more complicated than the ASCII code or the genetic code) by which mental concepts, words, images and episodic memories are translated into neural states. But no trace of any such system has ever been found, no one has given a credible detailed theory of how it could work, and if it existed it would be a “miracle of design” that would be naturally inexplicable.

If human brains actually stored conceptual and experiential memories, the human brain would have to have both a write mechanism by which exact information can be precisely written, and a read mechanism by which exact information can be precisely read. The brain seems to have neither of these things. There is nothing in the brain similar to the “read-write” heads found in computers.  

If memories were to be stored in a brain, it would take you "ages" to retrieve an answer to a question, because brains are totally lacking in any of the things that make fast retrieval possible: sorting, addresses and indexes. The brain has no type of addresses or coordinates or indexes. The brain has a structure in which neurons are rooted in place like trees in a forest, and synapses are rooted in place like the roots of trees in a forest. With such a physical arrangement, sorting is impossible. 

 So if memories were stored in brains, you would have to suffer the most ridiculously long delays every time you wanted to retrieve knowledge or a memory. 

As discussed here, humans can form new memories instantly, at a speed much faster than would be possible if we were using our brains to store such memories. It is typically claimed that memories are stored by “synapse strengthening” and protein synthesis, but such things are relatively sluggish processes that do not work fast enough to explain the formation of memories that can occur instantly.

For decades microscopes have been powerful enough to detect memories in brains, if memories existed in brains. Very much brain tissue has been studied by the most powerful microscopes: both brain tissue extracting from living patients, and brain tissue extracted from someone very soon after he died. Very many thousands of brains preserved soon after death have been microscopically examined.  Microscopes now allow us to see very clearly what is in the tiniest brain structures such as dendritic spines and synapse heads. But microscopic examination of brain tissue has failed to reveal any trace whatsoever of learned information in a brain.  No one has found a single letter of the alphabet stored in a brain; no has found a single number stored in a brain; and no one has ever found even a single pixel of something someone saw a day or more before.  If memories were stored in human brains, microscopes would have revealed decisive evidence of such a thing decades ago.  But no such evidence has appeared. 

There is nothing in the brain that looks like learned information stored according to some systematic format that humans understand or do not understand. Even when scientists cannot figure out a code used to store information, they often can detect hallmarks of encoded information. For example, long before Europeans were able to decipher how hieroglyphics worked, they were able to see a repetition of symbolic tokens that persuaded them that some type of coding system was being used. Nothing like that can be seen in the brain. We see zero signs that synapses or dendritic spines are any such things as encoded information. 

We know that human memory recall can occur massively with complete accuracy. There are numerous cases of people who memorized with complete accuracy the text of books of hundreds of pages. But synapses do not reliably transmit information. Scientists have repeatedly told us that an individual synapse will transmit a nerve signal with a reliability of 50% or less. So every time a nerve signal crosses a synapse, it is a coin flip as to whether that signal will be successfully carried across the synapse gap. So how could memories could ever be reliably retrieved from synapses? That would require a gigantic number of traversals across synaptic gaps, with a 50% chance of failure during each such traversal. You could never get perfect recall of large bodies of text from such a state of affairs, or even recall that was 10% accurate. 

The theory that human memories that can last for 50 years and can be instantly recalled are stored in synapses is a theory that contradicts pretty much everything we know about systems that can permanently store and instantly retrieve information, and contradicts everything we know about synapses, and contradicts everything we observe about the best examples of human memory performance. You could reasonably compare such a theory to the theory that certain clouds in the sky are nuclear missile bases set up by the Swiss to threaten your nation. That would pretty much contradict everything we know about the Swiss, everything we know about clouds, and everything we know about nuclear missile bases. 

But, you may say, "We should trust the theory of synaptic memory because all the neuroscientists believe in it." Do they really? We don't know that at all. To determine what percentage of neuroscientists believe the dogmas typically stated by neuroscientists, you need well-designed secret ballot opinion polls; and such polls are almost never done.  A recent study attempted to poll neuroscientists on their beliefs about memory storage.  The study (which you can read here) is entitled "What are memories made of? A survey of neuroscientists on the structural basis of long-term memory." 

Unfortunately the study fails to follow some of the main principles that should be followed by any study attempting to do an opinion poll of scientists. Specifically:

(1) The survey was not a secret ballot survey. Scientists were sent emails encouraging them to participate in the survey. The survey form promised anonymity, but it seemed like an arrangement where the participants had to trust that those running the survey would not reveal how individual scientists had voted. Anyone responding might have suspected that there might be some way in which his responses could be identified publicly as coming from him, if there were some future  breach in the promised confidentiality. 

Imagine you are a scientist getting an email like this:

Hello, Professor Waterskein. We have here a survey we would like you to fill out, asking you about all kinds of controversial questions. Please send it back to us. Don't worry, we won't ever publicly reveal which answers you gave. We'll only publish the collected results from the entire group of respondents. 

Are you going to feel it is safe to speak your mind? Or, are you going to still fear that somehow your answers might get you into trouble if they are too candid? I think you might tend to "play it safe" by assuming the person who sent you this email (who you know nothing about) cannot be trusted. 

Devising a true secret-ballot opinion poll (as opposed to a "promised anonymity" opinion poll) requires some cleverness and ingenuity, which did not go on in this case. So we can't know how much the responses were affected by scientists thinking "I had better answer as they expect me to answer."

(2) Contrary to all good standards of properly doing opinion polls, the badly fumbling survey organizers wrote a survey form in which the survey questions are preceded by statements strongly tending to bias  respondents towards a particular type of answer.  The survey form is found here. On page 4 of the survey form, before any questions are asked, we have the statement, "Memories are not standalone entities but are embedded within the complex network structure of the brain." Such a statement precedes questions about the nature of memory creation. But the statement "stacks the deck" in favor of a particular type of answer that could be given to one or more of the questions later asked. 

The clumsiness here is very big. It is a cardinal rule of serious polling that you should not precede questions with statements tending to yield particular types of responses to that questions. So, for example, if you are doing an objective poll about Presidential Candidate William Tygersoll, you absolutely should not precede your questions about this person with a statement such as "Here are some questions about that great American hero and patriot William Tygersoll."  Or, to give another example, if you polling people about some scandal involving this candidate, you absolutely should not be preceding your questions by some statement such as "Many are deeply upset about the scandal involving William Tygersoll. We would like to ask you your opinion."

Equally bad is that the survey conductors have stated on page 4 of their survey form this untrue claim: "Some studies have already demonstrated the ability to decode simple information such as visual field from brain maps (e.g. Scholl et. al. 2020." The reference is to the "no real evidence at all" study here involving a way-too-small sample size of only three monkeys. The quoted claim is an untrue one. The paper mentioned did not "demonstrate the ability to decode simple information such as visual field from brain maps."

Once again the scientists conducting the survey have violated the first rule of conducting a survey, which is "do not do anything to pre-sell a particular answer."  Here is Question 11 that appears in the survey form:

"11.Some neuroscientists have suggested that while molecular and subcellular details play a role, the majority of information for long-term memories is likely physically stored in the brain at the level of neuronal connectivity patterns and ensembles of synaptic strengths (e.g. Poo et al., 2016).

To what extent do you agree with the following statement: ' The structural basis of long-term memories primarily consists of lasting changes in neuronal connectivity and ensembles of synaptic strengths, rather than in molecular or subcellular details.'  "

This is a blunder from any standpoint of trying to objectively survey the opinion of scientists. We have a survey question that is preceded by a sentence pre-selling a particular answer to the survey question, as if the survey conductors were interested in pushing a particular response.  

Here are the responses the survey got from the question above asking neuroscientists about agreement with the following statement: "The structural basis of long-term memories primarily consists of lasting changes in neuronal connectivity and ensembles of synaptic strengths, rather than in molecular or subcellular details."

Strongly Agree:  51 respondents

Agree:  111 respondents

Not Sure: 37 respondents

Disagree:  26 respondents

Strongly Disagree: 5 respondents

So 68 out of 230 respondents (or about 29%) refused to endorse the synaptic theory of memory, even though the survey was strongly pre-selling such a theory. 13% flatly said they disagreed or strongly disagreed with such a theory.  We can only wonder how much higher that 29% figure would be if a true secret ballot had been used, and if the survey had followed proper standards of opinion surveying, such as not trying to pre-sell some answer to the questions it was asking. 

Clearly there is no consensus of neuroscientists about the theory that memories are stored in synapses. We are being misinformed when people try to suggest that such a consensus exists. A bad example of that type of misleading statement occurred in the paper "What is memory? The present state of the engram," a paper with many misstatements and many references to junk neuroscience studies failing to qualify as robust research. In that paper Mu-ming Poo stated, "There is now general consensus that persistent modification of the synaptic strength via LTP and LTD of pre-existing connections represents a primary mechanism for the formation of memory engrams." The new poll discussed above shows there is no such consensus. 

When someone tries to make a theory sound more popular than it is, they have done one of the bad deceits of science theory pitchmen. It's a deceit as old as the hills. It works by people trying to make some not-yet-triumphant theory gain more popularity by insinuating that almost everyone already believes in it. For a discussion of the trickery and equivocation and deceit that so often occurs in such cases, see my post "So Much Misleading Talk Occurs in Claims of a Scientific Consensus."

A better-designed poll might have asked a question such as this:

"Which reflects your thinking:

• 'Human memories are stored mainly in synapses.'
• 'Human memories are stored by some other brain mechanism, perhaps something involving neurons or brain chemistry.'
• 'Most memories are not stored in brains, and human memory is mostly a spiritual, psychic or metaphysical phenomenon, or some other subtle reality different from information storage in brains.'
• 'I don't know/no answer.'

Given a question such as this, and also a secret ballot not requiring respondents to trust the confidentiality of those doing a survey,  I doubt whether even 60% of neuroscientists would choose the first answer. 

The poll discussed above also shows us that most of those professing belief in the synaptic theory of memory lack a strong confidence in it. When given a set of poll choices allowing you to choose "agree" or "strongly agree," a mere 22% of the respondents chose to say that they "strongly agree" with the theory of synaptic memory storage. 

I have been generously referring above to a synaptic theory of memory, although it is probably more accurate to say that such a thing is not even a theory, but merely a small group of vague, vacuous jargon phrases repeated by scientists who have yet to develop a real theory on this topic. It's really a "there's no there there" situation. 

Given the huge diversity of the types of things that human can remember, an actual theory of neural memory encoding would require maybe 1,000,000 times more effort than involved in the production of the diagram above. 

Below are some relevant quotes, all statements by scientists:

• "Direct evidence that synaptic plasticity is the actual cellular mechanism for human learning and memory is lacking." -- 3 scientists, "Synaptic plasticity in human cortical circuits: cellular mechanisms of learning and memory in the human brain?" 
• "How the brain stores and retrieves memories is an important unsolved problem in neuroscience." --Achint Kumar, "A Model For Hierarchical Memory Storage in Piriform Cortex." 
• "We are still far from identifying the 'double helix' of memory—if one even exists. We do not have a clear idea of how long-term, specific information may be stored in the brain, into separate engrams that can be reactivated when relevant."  -- Two scientists, "Understanding the physical basis of memory: Molecular mechanisms of the engram."
• "There is no chain of reasonable inferences by means of which our present, albeit highly imperfect, view of the functional organization of the brain can be reconciled with the possibility of its acquiring, storing and retrieving nervous information by encoding such information in molecules of nucleic acid or protein." -- Molecular geneticist G. S. Stent, quoted in the paper here. 
• "Up to this point, we still don’t understand how we maintain memories in our brains for up to our entire lifetimes.”  --neuroscientist Sakina Palida.
• "The available evidence makes it extremely unlikely that synapses are the site of long-term memory storage for representational content (i.e., memory for 'facts'’ about quantities like space, time, and number)." --Samuel J. Gershman,  "The molecular memory code and synaptic plasticity: A synthesis."
• "Synapses are signal conductors, not symbols. They do not stand for anything. They convey information bearing signals between neurons, but they do not themselves convey information forward in time, as does, for example, a gene or a register in computer memory. No specifiable fact about the animal’s experience can be read off from the synapses that have been altered by that experience.” -- Two scientists, "Locating the engram: Should we look for plastic synapses or information- storing molecules?
• " If I wanted to transfer my memories into a machine, I would need to know what my memories are made of. But nobody knows." -- neuroscientist Guillaume Thierry (link). 
• "While a lot of studies have focused on memory processes such as memory consolidation and retrieval, very little is known about memory storage" -- scientific paper (link).
• "While LTP is assumed to be the neural correlate of learning and memory, no conclusive evidence has been produced to substantiate that when an organism learns LTP occurs in that organism’s brain or brain correlate."  -- PhD thesis of a scientist, 2007 (link). 
• "Memory retrieval is even more mysterious than storage. When I ask if you know Alex Ritchie, the answer is immediately obvious to you, and there is no good theory to explain how memory retrieval can happen so quickly." -- Neuroscientist David Eagleman.
• "How could that encoded information be retrieved and transcribed from the enduring structure into the transient signals that carry that same information to the computational machinery that acts on the information?....In the voluminous contemporary literature on the neurobiology of memory, there is no discussion of these questions."  ---  Neuroscientists C. R. Gallistel and Adam Philip King, "Memory and the Computational Brain: Why Cognitive Science Will Transform Neuroscience,"  preface. 
• "The very first thing that any computer scientist would want to know about a computer is how it writes to memory and reads from memory....Yet we do not really know how this most foundational element of computation is implemented in the brain."  -- Noam Chomsky and Robert C. Berwick, "Why Only Us? Language and Evolution," page 50. 
• "When we are looking for a mechanism that implements a read/write memory in the nervous system, looking at synaptic strength and connectivity patterns might be misleading for many reasons...Tentative evidence for the (classical) cognitive scientists' reservations toward the synapse as the locus of memory in the brain has accumulated....Changes in synaptic strength are not directly related to storage of new information in memory....The rate of synaptic turnover in absence of learning is actually so high that the newly formed connections (which supposedly encode the new memory) will have vanished in due time. It is worth noticing that these findings actually are to be expected when considering that synapses are made of proteins which are generally known to have a short lifetime...Synapses have been found to be constantly turning over in all parts of cortex that have been examined using two-photon microscopy so far...The synapse is probably an ill fit when looking for a basic memory mechanism in the nervous system." -- Scientist Patrick C. Trettenbrein, "The Demise of the Synapse As the Locus of Memory: A Looming Paradigm Shift? (link).
• "Most neuroscientists believe that memories are encoded by changing the strength of synaptic connections between neurons....Nevertheless, the question of whether memories are stored locally at synapses remains a point of contention. Some cognitive neuroscientists have argued that for the brain to work as a computational device, it must have the equivalent of a read/write memory and the synapse is far too complex to serve this purpose (Gaallistel and King, 2009; Trettenbrein, 2016). While it is conceptually simple for computers to store synaptic weights digitally using their read/write capabilities during deep learning, for biological systems no realistic biological mechanism has yet been proposed, or in my opinion could be envisioned, that would decode symbolic information in a series of molecular switches (Gaallistel and King, 2009) and then transform this information into specific synaptic weights." -- Neuroscientist Wayne S. Sossin (link).
• "We take up the question that will have been pressing on the minds of many readers ever since it became clear that we are profoundly skeptical about the hypothesis that the physical basis of memory is some form of synaptic plasticity, the only hypothesis that has ever been seriously considered by the neuroscience community. The obvious question is: Well, if it’s not synaptic plasticity, what is it? Here, we refuse to be drawn. We do not think we know what the mechanism of an addressable read/write memory is, and we have no faith in our ability to conjecture a correct answer."  -- Neuroscientists C. R. Gallistel and Adam Philip King, "Memory and the Computational Brain Why Cognitive Science Will Transform Neuroscience."  page Xvi (preface). 
• "Current theories of synaptic plasticity and network activity cannot explain learning, memory, and cognition."  -- Neuroscientist Hessameddin Akhlaghpourƚ (link). 
• "How memory is stored in the brain is unknown." -- Research proposal abstract written by scientists, 2025 (link). 
• "We don’t know how the brain stores anything, let alone words." -- Scientists David Poeppel and, William Idsardi, 2022 (link).
• "If we believe that memories are made of patterns of synaptic connections sculpted by experience, and if we know, behaviorally, that motor memories last a lifetime, then how can we explain the fact that individual synaptic spines are constantly turning over and that aggregate synaptic strengths are constantly fluctuating? How can the memories outlast their putative constitutive components?" --Neuroscientists Emilio Bizzi and Robert Ajemian (link).
• "After more than 70 years of research efforts by cognitive psychologists and neuroscientists, the question of where memory information is stored in the brain remains unresolved." -- Psychologist James Tee and engineering expert Desmond P. Taylor, "Where Is Memory Information Stored in the Brain?"
• "There is no such thing as encoding a perception...There is no such thing as a neural code...Nothing that one might find in the brain could possibly be a representation of the fact that one was told that Hastings was fought in 1066." -- M. R.  Bennett, Professor of Physiology at the University of Sydney (link).
• "No sense has been given to the idea of encoding or representing factual information in the neurons and synapses of the brain." -- M. R. Bennett, Professor of Physiology at the University of Sydney (link).
• ""Despite over a hundred years of research, the cellular/molecular mechanisms underlying learning and memory are still not completely understood. Many hypotheses have been proposed, but there is no consensus for any of these."  -- Two scientists in a 2024 paper (link). 
• "We have still not discovered the physical basis of memory, despite more than a century of efforts by many leading figures. Researchers searching for the physical basis of memory are looking for the wrong thing (the associative bond) in the wrong place (the synaptic junction), guided by an erroneous conception of what memory is and the role it plays in computation." --Neuroscientist C.R. Gallistel, "The Physical Basis of Memory," 2021.
• "To name but a few examples, the formation of memories and the basis of conscious  perception, crossing  the threshold  of  awareness, the  interplay  of  electrical  and  molecular-biochemical mechanisms of signal transduction at synapses, the role of glial cells in signal transduction and metabolism, the role of different brain states in the life-long reorganization of the synaptic structure or  the mechanism of how  cell  assemblies  generate a  concrete  cognitive  function are  all important processes that remain to be characterized." -- "The coming decade of digital brain research, a 2023 paper co-authored by more than 100 neuroscientists, one confessing scientists don't understand how a brain could store memories. 
• "The human brain isn’t really empty, of course. But it does not contain most of the things people think it does – not even simple things such as ‘memories’....We don’t create representations of visual stimuli, store them in a short-term memory buffer, and then transfer the representation into a long-term memory device. We don’t retrieve information or images or words from memory registers. Computers do all of these things, but organisms do not." -- Robert Epstein,  senior research psychologist, "The Empty Brain." 
• "Despite recent advancements in identifying engram cells, our understanding of their regulatory and functional mechanisms remains in its infancy." -- Scientists claiming erroneously in 2024 that there have been recent advancements in identifying engram cells, but confessing there is no understanding of how they work (link).
• "Study of the genetics of human memory is in its infancy though many genes have been investigated for their association to memory in humans and non-human animals."  -- Scientists in 2022 (link).
• "The neurobiology of memory is still in its infancy." -- Scientist in 2020 (link). 
• "The investigation of the neuroanatomical bases of semantic memory is in its infancy." -- 3 scientists, 2007 (link). 
• "Currently, our knowledge pertaining to the neural construct of intelligence and memory is in its infancy." -- Scientists, 2011 (link). 
•  "Very little is known about the underlying mechanisms for visual recognition memory."  -- two scientists (link). 
• "Conclusive evidence that specific long-term memory formation relies on dendritic growth and structural synaptic changes has proven elusive. Connectionist models of memory based on this hypothesis are confronted with the so-called plasticity stability dilemma or catastrophic interference. Other fundamental limitations of these models are the feature binding problem, the speed of learning, the capacity of the memory, the localisation in time of an event and the problem of spatio-temporal pattern generation."  -- Two scientists in 2022 (link). 
• "The mechanisms governing successful episodic memory formation, consolidation and retrieval remain elusive,"  - Bogdan Draganski, cogntive neuroscientist (link). 
• " The mechanisms underlying the formation and management of the memory traces are still poorly understood." -- Three scientists in 2023 (link). 
• "The underlying electrophysiological processes underlying memory formation and retrieval in humans remains very poorly understood." --  A scientist in 2021 (link). 
• "As for the explicit types of memory, the biological underpinning of this very long-lasting memory storage is not yet understood." -- Neuroscientist Cristina M. Alberini in a year 2025 paper (link).