Human Thoughts and Memory Are Gigantically Connective, But Brains Have Only Low Connectivity

The human mind and human memory are gigantically connective. A person's thoughts can quickly dart around between vastly different areas of human knowledge. For example, suppose you ask me, "How could modern technology have made a difference if the ancient Romans had possessed it?" Darting around instantly between many different pieces of knowledge in my memory, I might very quickly give an answer like this:

"It's easy to think of many different ways modern technology could have made a difference around the time of Julius Caesar and Octavian. Julius Caesar might have avoided his assassination, maybe by wearing a Kevlar vest and Kevlar collar, or maybe by installing metal detectors at the Senate building. Mark Antony might have won the battle of Actium, by having jet fighters bomb the ships of Octavian into pieces. The Romans might have used tanks and bombers to wipe out the barbarian hordes, preventing the fall of Rome from ever happening. And with smartphones and TV helping everyone to instantly communicate, there would been none of the 'too big an empire' problem that plagued the Romans. The Roman empire might have spread across half of Eurasia."

Or, to give another example, when asking myself, "Name some famous Johns," I quickly wrote down the following, extracting things from a variety of historical eras, and from both fact and fiction:

"Well there's Prince John and Little John in the Robin Hood story. And there's John the author of one of the gospels. Then there's John Updike, an American writer. And there's the famous assassin John Wilkes Booth. Then there's Pope John Paul II. And there's John Lennon.  And Johnny Walker and Johnny Carson. Then there's US presidents John Adams and John Quincy Adams. Then there's John Brown who raided Harper's Ferry. And don't forget the scientist John Dalton."

It seems that the human mind and human memory are gigantically connective. But does the human brain have any degree of connectivity that can explain the almost perfect connectivity of the human mind and human memory? A person might claim that the brain has perfect connectivity, on the grounds that it is possible to trace a path between any two regions of the brain. But it would be hasty to draw a conclusion about brain connectivity from so simple a fact. Analyzing how connective the brain is turns out to be a much more complicated task. 

Neurons in the brain can be analyzed as nodes in a network. With any network there are ways of quantifying how connective the network is. Some important questions may be asked to judge the connectivity of a network:

(1) What is the ratio between the total number of nodes in the network and the total number of connections between nodes in the network?

(2) What percentage of the total nodes in the network is the average node in the network directly connected to?

(3) What is the average time needed to communicate between two random nodes of the network?

(4) How reliably does a signal travel between two nodes in the network?

Let me give some very simple examples of answering some of these questions. Let's consider the very simple network shown below:

Here is a partial analysis of this network's connectivity:

Number of nodes: 7.

Number of connections: 12.

Average number of connections per node: 3.28.

What fraction of the total nodes in the network is the average node in the network directly connected to? 3.28 divided by 7, or .468

A network with  higher connectivity is shown below:

Here is a partial analysis of this network's connectivity:

Number of nodes: 7.

Number of connections: 17.

Average number of connections per node: 4.57.

What fraction of the total nodes in the network is the average node in the network directly connected to? 4.57 divided by 7, or .65, which is roughly two-thirds.

It is the last question that gives us the "bottom line" on how much connectivity the network has. The first network has a "bottom line" connectivity of only .468, but the second network has a substantially higher "bottom line" connectivity of .65.  A network with perfect connectivity would have a "bottom line" connectivity of 1.0. 

Now, having got a bit "warmed up" in analyzing the connectivity of networks, let us consider the question: just how connective is the human brain? We can use the same format as above.

Number of nodes: about 100 billion (which is the number of neurons in the human brain).

Number of connections: about 100 trillion (which is the number of synapses in the human brain, each neuron having an average of about 1000 synapses).

Average number of connections per node: about 1000. Although it is sometimes claimed there are thousands of synapses per neuron, the 2021 study here (Table 1) finds fewer than 100 connections per neuron in primates, finding 25 excitatory synapses per neuron in primates and 44 inhibitory synapses per neuron in primates.

What percentage of the total nodes in the network is the average node in the network directly connected to? 1000 divided by 100 billion, or 0.00000001.

We are left with a shockingly low "bottom line" number on the connectivity of the human brain. The human brain would seem to have a connectivity very, very many times lower than the two networks depicted above. The "bottom line" connectivity of the brain is a number only about 1 in 100 million. 

Here are some interesting findings from the neuroscience literature. The source here says, "Electrophysiological studies detect connections only in approximately 10% of pairs of neurons." This would seem to mean that when scientists check whether two neurons right next to each other are connected, they find that in only about 1 case in 10 are such neurons connected. Referring to a type of brain structure in which neurons are rather densely packed (pyramidal cells), the paper states, "Virtually all electrophysiological studies in vitro find connection probabilities of order 0.1–0.2 for pairs of nearby pyramidal cells."

Using older and different estimates about the number of brain cells and the number of connections (synapses) between brain cells, a scientific paper ("Is the brain really a small-world network?") states the following:

"On average, the density of human brain connectivity at the cellular level is very sparse. The average number of synapses of neurons (~104) (Braitenberg and Schüz 1998) divided by the number of neural elements (~1010) (Herculano-Houzel 2012) results in a very low average probability of any two neurons in the brain making contact (10−6), implying a highly dispersed network." 

The paragraph above is telling us that if you were to pick two random neurons in the brain, there would be only about 1 chance in a million that they are directly connected. It seems that the connectivity of neurons in the brain is very low, way too low to explain the almost perfect connectivity of ideas, thoughts and memories in the human mind. 

There are two other crucial factors we should consider when considering the connectivity of the brain:

(1) How fast do signals travel between neurons?

(2) How reliably does a signal travel when it passes between two neurons?

Considering the first of these questions, the widely quoted figure of about 100 meters per second for brain signals is very misleading. That is the fastest that a signal can travel in any part of the brain, when signals pass through myelinated axons. But most axons in the cortex are not myelinated, and most of the tissue in the brain consists of relatively slow dendrites. According to neuroscientist Nikolaos C Aggelopoulos, there is an estimate of 0.5 meters per second for the speed of nerve transmission across dendrites (see here for a similar estimate). That is a speed 200 times slower than the nerve transmission speed commonly quoted for myelinated axons. Then there is the enormous slowing factor caused by the need for brain signals to cross across synapses, serious "speed bumps" that should slow down brain signals very much. 

There is a scientific term used for the delay caused when a nerve signal travels across a synapse. The delay is called the synaptic delay. According to this 1965 scientific paper, most synaptic delays are about .5 milliseconds, but there are also quite a few as long as 2 to 4 milliseconds. A more recent (and probably more reliable) estimate was made in a 2000 paper studying the prefrontal monkey cortex. That paper says, "the synaptic delay, estimated from the y-axis intercepts of the linear regressions, was 2.29" milliseconds. It is very important to realize that this synaptic delay is not the total delay caused by a nerve signal as it passes across different synapses. The synaptic delay is the delay caused each and every time that the nerve signal passes across a synapse. 

Such a delay may not seem like too much of a speed bump. But consider just how many such "synaptic delays" would have to occur for, say, a brain signal to travel from one region of the brain to another. It has been estimated that the brain contains 100 trillion synapses (a neuron may have thousands of them).  So it would seem that for a neural signal to travel from one part of the brain to another part of the brain that is a distance away only 5% or 10% of the length of the brain, that such a signal would have to endure many thousands of such "synaptic delays" requiring a total of quite a few seconds of time. 

There is no reason to think that the average speed of signals in the brain should be much faster than the speed at which electrical signals travel around the brain during seizures. The paper here lists a speed of only about 1 millimeter per second for seizures in the human brain, saying, "Seizures propagate slowly to connected areas with speeds on the order of 1 mm/s."  There is no reason to think that some hypothetical brain signals involved in thinking would occur much faster than seizures. 

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."

Such a result (a very serious brain physical shortfall) is surprising only to those who believe that your brain stores your memories and that your brain makes your mind.  Those who disbelieve such a thing may expect exactly such shortfalls to be repeatedly found. 

To summarize, there are three gigantic reasons why a human brain cannot be regarded as any kind of high-connectivity network:

(1) The "bottom line" connectivity of the brain (as defined above) is very low, with the average neuron being directly connected to fewer than 1 in a million of the brain's neurons, and as few as 1 in 100 million of the brain's neurons. 

(2) You cannot assume that this shortfall is fixed by signals traveling reliably between many neurons (such as from Neuron 1 to Neuron 2 to Neuron 3 to Neuron 4 to Neuron 5 to Neuron 6), because the reliability of signal transmission across synapses is so low that the signal would very probably be lost when even trying to pass across only four different neurons.

(3) Very serious slowing factors such as the low transmission speed of dendrites and synaptic delays should worsen brain connectivity even further. 

Your mind and memory are almost perfectly connective. But your brain has poor physical connectivity. Such a discrepancy is one of very many reasons for thinking that your brain cannot be the source of your mind. 

Postscript: The 2022 paper "What Kind of Network Is the Brain?" by John D. Mollon  and others gives us some facts that cast doubt on claims that the brain is a very highly connected network. We read this:

"Excluding callosal neurons, efferent neurons, and all non-pyramidal cells, they estimate that the total number of neurons making ipsilateral connections within one hemisphere is 6 × 10⁹. However, they estimate that there are only ~10⁸ axons in all the major long-range tracts combined. Thus, of all the cells that make cortico-cortical connections, most are local in their projections, and only ~2% have access to the long-range tracts within one hemisphere (and the proportion having access to any individual tract is likely to be still smaller) [46]. The proportion of non-efferent cells contributing axons to the corpus callosum is similarly ~2%.

The estimates obtained by Schüz and Braitenberg were based on classical histology, but they draw confirmation from a recent analysis of diffusion MRI (dMRI) data. Rosen and Halgren [48] analyzed tractography data for 1065 individuals in the Human Connectome Project. They calibrated their dMRI measure by reference to the known density of axons in the corpus callosum and the cross-sectional area of the corpus callosum of each individual (obtained by structural MRI). They then used this conversion factor to estimate the number of axons in the long-distance fasciculi. For each of the 360 'parcels' [49] of cortex, they calculated the number of fibers connecting to every other parcel. Long-range connections (callosal plus intra-hemispheric) were sparse, about 3.7% in total – a value close to Schüz and Braitenberg's estimate of 4%. The limited capacity of the long-distance tracts is difficult to reconcile with models that suppose the brain is a meta-net [9] or with accounts of memory in which cell assemblies depend on many long-range excitatory connections. [50]"

The 2022 paper "An estimation of the absolute number of axons indicates that human cortical areas are sparsely connected" found that human cortical areas are "sparsely connected," contrary to popular depictions of a brain in which all the neurons are very highly connected. The paper makes this revealing statement:  "We find that the widespread cortical integration implied by behavioral and  mental coherence, and routinely observed in widespread physiological synchronization, belies a surprising small absolute number of long-range axons connecting cortical areas."  In other words, human mental performance tells one story, and your brain tells another story not expected from human mental performance.  This is just what we might expect if the brain is not the source of the human mind. 

Why a Brain Should Be Unable to Reliably Transmit Any Memory or Thought Signal

When neuroscientists attempt to describe electrochemical effects moving around in the brain, they describe it in terms of what is called an action potential.  An action potential is an electrical change in a neuron which can be transmitted to other nearby neurons.  Now, there is a related question very relevant to the issue of whether the brain can actually be the storage place of human memory or the source of human thought. This question is: can these action potentials make up reliable memory signals or thought signals that travel around in the brain?  For example:

1. Could a brain retrieve some memory information stored in one part of a brain, and send that information reliably (as a kind of coherent signal) from one part of the brain to another part of the brain (perhaps from one part storing the information to another part more involved in attention or current thought)? 
2. Could a brain send some information arising from thinking from one part of a brain to another part (something that would presumably be necessary for a brain to have complex thoughts combining simpler ideas)?

In previous posts on this site I have discussed a major reason for thinking that the answer to the first question must be: no. The reason is that information does not reliably transfer across the synapses that separate neurons. It has been established that action potentials only travel across synapses with a likelihood of about 50% or less (some estimates are as low as 10% or 20%).  So if the brain tried to retrieve detailed information (such as a sentence of text) from one part of the brain to another, and each synapse transmitted an action potential with a likelihood of less than 50%, than the information would not be reliably transmitted.  

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."

Such a result (a very serious brain physical shortfall) is surprising only to those who believe that your brain stores your memories and that your brain makes your mind.  Those who disbelieve such a thing may expect exactly such shortfalls to be repeatedly found. 

In the brain, information would need to travel though very many synapses for even a short trip in the brain. What analogy can we give for such a setup, if each trip across a synapse occurs with low reliability? An analogy would be if I send an email from New York to Los Angeles, with the email passing through seven different computer servers, each of which transmits each particular character  with a reliability of less than 50%.  Under such a setup, it would be a lucky if a single word of my email got from New York to Los Angeles.  There would be such message garbling and loss of characters that it would be a kind of like trying to read a pen-written message on a piece of paper that had gone through a washing machine seven different times. 

There is another major reason for thinking that a brain should be unable to transmit any memory or thought signals. The reason is that most neurons have so many connections that there would be a signal overload preventing the reliable transmission of information. 

Let us consider three different devices that effectively transmit information: a computer with a simple web browser,  a radio and a television.  There is one very important thing common to each of these inventions: each is arranged so that signals are received from only one source at a time.  For example:

• A television set is arranged so that it can display TV signals from only one TV channel at a time.
• A radio is set up so that it can receive signals from only one radio station at a time.
• A computer with a simple web browser can display information from only one URL or web site at a time (let's ignore the not-so-simple web browsers that allow you to display different web sites in different tabs, and ignore the possibility of bringing up multiple instances of a web browser on the same computer). 

Now, let's imagine what chaos would result if these things were not arranged in such a way:

• If a television set were arranged so that it displayed TV signals from five or ten TV channels at the same time, you would see and hear such a confusion of pixels and sounds that you would not be able to understand or enjoy any of the channels.
• If a radio were set up so that it received signals from five or ten different radio stations at a time, you would probably get such a confusion of sounds you would not be able to understand or enjoy anything coming from the radio.
• If a computer used a web browser that displayed five or ten web pages all at the same time, the browser's screen would show such a confusion of pixels that you would not be able to understand anything. 

For example, if your TV set displayed five stations at the same time, you might see something like the jumble below, which would not be coherent, intelligible information. 

What we know about the physical arrangement of the brain tells us that the brain should suffer from the same type of problem described above. Since each neuron is bombarded with signals from many other neurons, most of which fire randomly, it should be impossible for neurons to accurately transmit thought or memory signals.  It has been estimated that the average neuron has 7000 connections to other neurons. Every neuron should be like some malfunctioning TV set that picks up simultaneously 100 different TV stations at the same time, resulting in an incomprehensible jumble like the jumble shown above. 

Below we see a diagram of a neuron. The yellow part is a myelinated axon, and the orange parts are dendrites.  

For anyone who thinks that a neuron receives an "action potential" (AP)  nerve signal only from an axon, the article here tells us the following:

"In fact, dendrites can be the site of AP initiation and propagation, and even neurotransmitter release. In several interneuron types, all functions are carried out by dendrites as these neurons are devoid of a canonical axon."

The wikipedia.org article on dendritic spikes tells us the following:

"In neurophysiology, a dendritic spike refers to an action potential generated in the dendrite of a neuron. Dendrites are branched extensions of a neuron. They receive electrical signals emitted from projecting neurons and transfer these signals to the cell body, or soma. Dendritic signaling has traditionally been viewed as a passive mode of electrical signaling. Unlike its axon counterpart which can generate signals through action potentials, dendrites were believed to only have the ability to propagate electrical signals by physical means: changes in conductance, length, cross sectional area, etc. However, the existence of dendritic spikes was proposed and demonstrated by W. Alden Spencer, Eric Kandel, Rodolfo Llinás and coworkers in the 1960s[1][2] and a large body of evidence now makes it clear that dendrites are active neuronal structures. Dendrites contain voltage-gated ion channels giving them the ability to generate action potentials."

Given such realities, we can describe a neuron as being subject to the most severe signal overload, like some TV set that is getting 100 channels at once, or some radio picking up 100 stations at once. Given the physical arrangement of neurons in brains, there is no chance that memory signals or thought signals could be reliably transmitted by neurons. Given many signal-slowing factors discussed at length here, it should be impossible for signals to travel through the human cortex at much faster than a snail's pace.  Yet humans can think and recall with the greatest speed and accuracy. This is shown by cases such as actors playing the role of Hamlet, who recall more than 4000 lines with perfect accuracy, and at high speed. It is also shown by calculation savants who do extremely complicated mathematical calculations in their mind very quickly with perfect accuracy. 

There are many historical cases of math prodigies that could calculate with incredible speed and accuracy.  The passage below describes the blazing fast and very accurate calculation powers of Zerah Colburn:

"This child undertook, and completely succeeded in, raising the number 8 progressively up to the sixteenth power. And in naming the last result, viz.: 281, 474, 976, 710, 656, he was right in every figure. He was then tried as to other numbers consisting of one figure, all of which he raised (by actual multiplication, and not by memory) as high as the tenth power, with so much facility and dispatch that the person appointed to take down the results was obliged to enjoin him not to be so rapid. With respect to numbers consisting of two figures, he would raise some of them to the sixth, seventh and eighth power....He was asked the square root of I06,929, and before the number could be written, he immediately answered, 327. He was then required to name the cube root of 268,336,125, and with equal facility and promptness he replied, 645. Various other questions of a similar nature, respecting the the roots and powers of very high numbers, were proposed by several of the gentlemen present, to all of which he answered in a similar manner. One of the party requested him to name the factors which produced the number 247,483: this he immediately did by mentioning the numbers 941 and 263 — which, indeed, are the only two numbers that will produce it...One of the gentlemen asked him how many minutes there were in forty-eight years; and before the question could be written down, he replied 25,228,800; and instantly added that the number of seconds in the same period was 1,513,728,000."

The passage below tells us about the incredibly fast and accurate calculation speed of  Jacques Inaudi, born in 1867:

"In his exercises of mental calculation, Mr. Inaudi is remarkable in two particulars, the complexity of his work and the rapidity with which he completes it. The greater number of questions given to him contain many figures. He will add in his head two numbers consisting of twelve figures each ; he will multiply two numbers composed of eight figures ; he will tell how many seconds there are in any promiscuously chosen number of years, months, days, and hours. These operations demand that he shall hold in his memory the exact problem and the partial solutions up to the time when the complete result is found. For such a considerable work as this, Mr. Inaudi gives an extremely short time, so short, indeed, as sometimes to produce the illusion of instantaneity. The following paragraph has been published concerning him. 'He adds in a few seconds seven numbers of eight or ten figures each; he subtracts one number from another each composed of twenty-one figures in less than a minute; he finds as rapidly the square root or the cube root of numbers consisting of from eight to twelve figures, if these numbers are perfect squares or cubes; it takes a little longer for the last-named work if there is a remainder necessitating a fractional part to the answer. He finds with incredible celerity the sixth or the seventh root of large numbers. He will multiply or divide in less time than it takes him to announce the results. As an example of what has been said, we give the following: He was asked the number of seconds in 18 years, 7 months, 21 days and 3 hours. The response was given in thirteen seconds.' "

The gap between the physical shortcomings of the brain and the realities of the most impressive human mental performance is like the gap between Earth and Jupiter. It is therefore foolish to continue the speech custom of saying that thinking and recall comes from brains, a custom that is an example of hollow hubris.  It would be far wiser for us to say, "Humans have magnificent mental powers, and we don't know where they come from."

"Brains Store Memories" Dogma Versus the Reality of Noisy Brains

Neuroscientists typically maintain that human mental phenomena are entirely produced by the brain. But this claim is inconsistent with many low-level facts that neuroscientists have discovered. Remarkably, the facts and details that neuroscientists have learned on a low level frequently contradict the dogmatic high-level assertions neuroscientists make.

The table below summarizes this conflict.

High-level Neuroscientist Claims	Low-Level Facts Discovered by Neuroscientists
“Brains produce thinking”	Human cognitive ability and memory is not strongly damaged by hemispherectomy operations in which half of a brain is removed to treat epilepsy seizures.
	Most of Lorber's hydrocephalus patients with brains mostly consisting of watery fluid had above average intelligence, and a Frenchman was able to long hold a civil service job while almost all of his brain was gone.
	Brain scans do not show brains working significantly harder during either heavy thinking or recall, and no signal change greater than 1% occurs during such activities.
“When we do accurate mental calculations, it is our neurons that are doing the work”	Neurons are noisy, and synapses transmit signals with only a 50% likelihood or less– the type of thing that should prevent accurate mental arithmetic as savants can perform.
“Our memories are stored in our brains”	Neurons and synapses have been extensively examined at very high microscopic resolutions, and no sign of stored information or encoded information has been found in them other than the gene information in DNA.
	There is high protein turnover in the synapses that neuroscientists claim to be the storage place of memories, and the average lifetime of the proteins that make up synapses is only a few weeks – only a thousandth of the lifespan of very old memories in old people.
	There seems to be nothing in the human brain resembling the write mechanism like we see in storage systems such as computers.
“When we remember, we read data from our brains.”	There seems to be nothing in the human brain resembling the read mechanism like we see in storage systems such as computers.
	There is in the human brain no position coordinate system, no indexing, no neuron numbering system, nor anything else that would seem to make possible an instantaneous recall of information from some very precise location in a brain, in a manner similar to a retrieval of data from a particular page of a particular book
	Although we would expect information to be reliably transmitted across neurons during precise and accurate human recall, neurons are actually quite noisy, and transmit signals with only a low reliability.
	Synaptic density studies show that the the density of synapses in brains strongly drops between puberty and adulthood, at the very time when learned knowledge is piling up.

By following the links above, you can read detailed discussions of the claims I make in the right column – except for my claims about neurons being very noisy, which I will justify in this post. 

When we talk about the noise in a communication system, we can imagine this as a kind of static that prevents the transmission from occurring without errors. A young reader may not even know what static is, since nowadays digital communication occurs with very little noise. But I experienced static frequently in my youth, back in the days long before the internet. One type of static would occur when I listened to the radio. When I tuned in to a radio station too far away, the radio signal would be mixed with a crackling noise or static that might prevent me from hearing particular words or musical notes in the transmission. In my youth there was also a problem with television noise or static. On top of a TV set there would be an antenna, and if it wasn't pointing just right, a TV signal might be rather noisy. The noise might be of a visual type, with random little blips appearing on the TV screen. Sometimes the static would be so bad you couldn't see much of anything on the TV you recognized.

The table below illustrates an example of noise in a signal transmission system.

Type of system	Input	Output
Low-noise system	“Toto, I've a feeling we're not in Kansas anymore.”	“Toto, I've a feeling we're not in Kansas anymore.”
High-noise system	“Toto, I've a feeling we're not in Kansas anymore.”	“Tojo, I've a f2@eling we're Xot in K3$sas anymore.”

A neuron acts as an electrical/chemical signal transmitter. A neuron will receive an electrical/chemical input, and transmit an electrical/chemical output. But a neuron does not act as efficiently and reliably as a cable TV wire or a computer cable that transmits signals with a very low error rate. Neuroscientists know that a large amount of noise occurs when neurons transmit signals. In other words, when a neuron receives a particular electrical/chemical input signal, there is a very significant amount of chance and variability involved in what type of electrical/chemical output will come out of the neuron. The wikipedia.org article on “neuronal noise” identifies many different types of noise that might degrade neuron performance: thermal noise, ionic conductance noise, ion pump noise, ion channel shot noise, synaptic release noise, synaptic bombardment, and connectivity noise.

In a very recent 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."

So according to this expert, synapses (the supposed storage place of human memories) transmit signals with a probability of less than 50 percent. Now that's very heavy noise – the kind of noise you would have if half of the characters in your text messages got scrambled by your cell phone carrier.  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."

Such a result (a very serious brain physical shortfall) is surprising only to those who believe that your brain stores your memories and that your brain makes your mind.  Those who disbelieve such a thing may expect exactly such shortfalls to be repeatedly found. 

Another scientific paper tells us, “Neuronal variability (both in and across trials) can exhibit statistical characteristics (such as the mean and variance) that match those of random processes.” Another scientific paper tells us that “Neural activity in the mammalian brain is notoriously variable/noisy over time.” Another paper tells us, "We have confirmed that synaptic transmission at excitatory synapses is generally quite unreliable, with failure rates usually in excess of 0.5 [50%]." A paper tells us that there are two problems in synaptic transmission: (1) the low likelihood of a signal transmitting across a synapse, and (2) a randomness in the strength of the signal that is transmitted if such a signal transmission occurs. As the paper puts it (using more technical language than I just used):

The probability of vesicle release is known to be generally low (0.1 to 0.4) from in vitro studies in some vertebrate and invertebrate systems (Stevens, 1994). This unreliability is further compounded by the trial-to-trial variability in the amplitude of the post-synaptic response to a vesicular release. 

The 2010 paper "The low synaptic release probability in vivo" by Borst is devoted to the topic of what is the chance that a synapse will transmit a signal that it receives. It tells us, "A precise estimate of the in vivo release probability is difficult," but that "it can be expected to be closer to 0.1 than to the previous estimates of around 0.5." 

Another paper concurs by also saying that there are two problems (unreliable synaptic transmission and a randomness in the signal strength when the transmission occurs):

On average most synapses respond to only less than half of the presynaptic spikes, and if they respond, the amplitude of the postsynaptic current varies. This high degree of unreliability has been puzzling as it impairs information transmission.

This is a problem for all claims that memories are retrieved from brains, because humans are known to be able to remember things very accurately, but “neural noise limits the fidelity of representations in the brain,” as a scientific paper tells us.

Now, a neuroscientist might claim that such facts can still be reconciled with the mental performance of humans. He might argue like this:

Yes, neurons and synapses are pretty slow and noisy, but that's why human memory is slow and unreliable. Think of how it works when you suddenly see some old schoolmate that you haven't seen in twenty years. It may be a while before you remember their name. And when you remember something about that person, your memory will probably be not terribly accurate. So you have a kind of a slow “noisy” memory.

But it is easy to come up with examples of human memory performing without error in a noiseless manner. I just closed my eyes and recited the following lines without any error at a rate faster than you can read these lines aloud:

I am the very model of a modern Major-General

I've information vegetable, animal, and mineral
I know the kings of England, and I quote the fights historical
From Marathon to Waterloo, in order categorical

I'm very well acquainted, too, with matters mathematical
I understand equations, both the simple and quadratical
About binomial theorem I'm teeming with a lot o' news
With many cheerful facts about the square of the hypotenuse

But that's not very impressive, for there are singers who can flawlessly sing without any errors at a very rapid pace the entire delightful song “I Am the Very Model of a Modern Major General” from Gilbert and Sullivan's “The Pirates of Penzance,” and the song is about eight times longer than what I have quoted. Also, in the world of opera there are singers who can flawlessly sing every note and every word of the part of Hans Sachs in Wagner's four-hour opera Die Meistersinger von Nurnberg, an opera in which Hans is on stage singing for a large fraction of those four-hours. There are other singers who can flawlessly sing the title role in the opera Siegfried, which requires the lead singer to sing on stage for most of its three hours. There are other singers who can flawlessly sing the role of Tristan, which also requires a similar demand. In such cases we have a very rapid and flawless error-free retrieval of an amount of information that would take many, many pages to write down.

A rock singer at a funky free-wheeling concert might get away with an error rate of 2% in his memory recall of words, but opera fans are very intolerant of errors. When Wagner fans (who have typically heard an opera many times on recordings) go to something like the Bayreuth festival, they expect singers to recall Wagner's notes and words with 100% fidelity, and that is what they usually get, even when hearing roles such as Tristan and Siegfried which require a singer to memorize hours of singing.  Every time an actor performs Hamlet, he recites 1480 lines of dialog, and many such actors recall all such lines without any errors. 

Then there is Leslie Lemke, who according to this article in wikipedia.org "can remember and play back a musical piece of any length flawlessly after hearing it once."  It is well documented that there are quite a few Muslims who can recite the entire holy book of their religion, a book of some 80,000 words. Then there are people who flawlessly remember content that is hard to remember. According to the site of the Guiness Book of World Records, Rajveer Meena memorized pi to 70,000 digits, reciting those 70,000 digits without any errors. Lu Chao memorized pi to 67,000 digits. A 1917 scientific paper stated that one or more people had accurately "memorized the exact layout of words in more than 5,000 pages of the 12 books of the standard edition of the Babylonian Talmud."

How could such feats occur if memory retrieval is being performed by neurons and synapses that are very noisy? They cannot be. In these cases, human memory is acting at a reliability vastly surpassing what should be possible if memory retrieval or thought is a neural phenomenon.  A scientific paper states, "Neural noise limits the fidelity of representations in the brain."  But humans such as those I have mentioned seem to be able to recall huge amounts of learned text or song without any such problem of a degradation of "fidelity of representations." 

A similar conclusion is forced on us when we consider the accuracy of the most impressive human calculators. In 2004 Alexis Lemaire was able to calculate in his head the 13th root of this number:

85,877,066,894,718,045, 602,549,144,850,158,599,202,771,247,748,960,878,023,151, 390,314,284,284,465,842,798,373,290,242,826,571,823,153, 045,030,300,932,591,615,405,929,429,773,640,895,967,991,430,381,763,526,613,357,308,674,592,650,724,521,841,103,664,923,661,204,223

In only 77 seconds, according to the BBC, Lemaire was able to state that it is the number 2396232838850303 which when multiplied by itself 13 times equals the number above.  Here we have calculation accuracy far beyond anything that could be possible if noisy neurons are the source of human thought. 

Given the high amount of noise in neurons and synapses, which would strongly degrade the accuracy of neural memory retrieval and neural signal transmission, the facts of very accurate human calculation and very accurate human memory recall (as shown by calculation savants, Hamlet actors, and Wagnerian opera singers) are very much in conflict with the dogmas that our thinking is performed by our brains and our memories are stored in and retrieved by our brains.  This is yet another case in which the low-level facts of neuroscience defy the dogmatic claims of neuroscientists. 

Think for a moment about the implications if a synapse can only transmit a signal with about a 50% reliability, as indicated by the previously quoted expert on neuron noise. This does not at all mean that people would recall things with about 50% accuracy if memories are stored in brains; it's much worse than that. Since any act of neural memory retrieval would involve innumerable different signal transmissions through innumerable neurons, we would expect the actual accuracy to be only some tiny fraction of 50% if we were using synapses to retrieve our learned knowledge.  Similarly, if you play the game "Chinese whispers" (also called "gossip") at a school lunch table, and have everyone at the table be playing noisy music in earphones as they hear the gossip story being whispered among the players, the tenth person to receive the story will be unlikely to receive even 20 percent of it accurately. 

Let us imagine a planet in which the sky was perpetually covered in very thick clouds, so that no one had seen the stars or the local sun.  On such a planet there would be a great mystery: from where comes the heat that keeps life on the planet warm? If you were a rather clumsy thinker on such a planet, you might come up with some cheesy theory to explain the heat on your planet, and dogmatically cling to it -- maybe the theory that rocks on your planet warm the planet through radioactivity, or that heat shoots up from the hot core of the planet. But if you were a better thinker, you would say, "There is nothing anyone has observed that can explain this planet's heat -- it must come from some mysterious unseen reality."  It is something similar that we should say about our mental capabilities: that nothing we have observed can explain them, and that they must come mainly from some mysterious unseen reality. 

Postscript:  It is sometimes suggested that by transmission redundancy we can escape the consequences of unreliable and noisy synaptic transmission (in which signals may travel across a synapse only 50% of the time or as little as 10% of the time). But this paper makes clear that in the cortex of the brain there is little such redundancy. It states the following:

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 . In other words, as many as nine out of ten presynaptic stimuli fail to trigger transmitter release. The critical difference between these cortical connections and those at the neuromuscular junction is that, in the cortex, the synaptic connection between a pair of cells is often made up of only a few release sites, sometimes only one [6], [7]. In the cortex, then, the postsynaptic response to a single presynaptic action potential is highly variable, because it is the average over a small and unreliable population....In the periphery [of the brain], reliability is achieved by averaging over many release sites. In the cortex, rich interconnectivity within a restricted volume limits the possible number of such redundant connections.