An example of such a thing is an article that appeared in the online site of the major British newspaper The Guardian. The article by neuroscientist Dean Burnett was entitled "What happens in your brain when you make a memory?" Burnett follows a kind of standard formula followed by writers on this topic. The rules are rather as follows:
(1) Attempt to persuade readers that you understand memory by talking about the difference between long-term memory and short-term memory. Whenever such discussion occurs, it actually does nothing showing any understanding of a neural basis for memory, for such a discussion can occur based on purely phenomenal observations about how well people perform on different memory tasks.
(2) Attempt to persuade readers that you understand memory by talking about the difference between episodic memory and conceptual memory. This again is something that can be discussed without any reference to the brain, so any such discussion doesn't do anything to establish some understanding of a neural basis for memory.
(3) Make frequent use of the word "encoding," without actually presenting any theory of encoding. Neuroscientists love to use the word "encoding" when discussing memory acquistion, as if they had some understanding of some system of encoding or translation by which episodic or conceptual memories could be translated into neural states or synapse states. They do not have any such understanding. No neuroscientist has ever presented a credible, coherent, detailed theory of memory encoding, of how conceptual knowledge or episodic experiences could ever be translated into neural states or synapse states. Any attempt to do such thing would cause you to become entangled in an ocean of difficulties.
(4) Mention one or two parts of the brain, usually exaggerating their significance. I'll give an example of this in a moment.
(5) Talk dogmatically about synapses, creating the impression that memories are stored in them, without discussing their enormous instability and unsuitability as a place for storing memories that might last for decades.
Burnett pretty much follows such a customary set of rules. He uses the word "encoding" or "encode" four times, but fails to present any substantive explanation or idea as to how any human episodic or conceptual information could ever be encoded, in the sense of being translated into neural states. Burnett claims, "The hippocampus links all of the relevant information together and encodes it into a new memory by forming new synapses." He provides no evidence to back up this claim. There are some important reasons for thinking that the claim cannot possibly be correct.
One reason is that studies have shown that people with very heavy hippocampus damage can have a normal ability to acquire conceptual and learned information. The paper here discussed three subjects who had lost about half of the matter in their hippocampi. We read the following:
The same thing was found by the study here. A group of 18 subjects were studied, subjects with severe hippocampus damage. Some 28% to 62% of the hippocampi of these subjects were damaged or destroyed. The subjects had episodic memory problems, but "relatively preserved intelligence, language abilities, and academic attainments." We are told, "In all but one of our cases, the patients...attended mainstream schools." Could patients with such heavy hippocampus damage have normal academic achievements if it were true that "the hippocampus links all of the relevant information together and encodes it into a new memory by forming new synapses"? Not at all. In a similar vein, the study here involving 17 rhesus monkeys found that "monkeys with hippocampal lesions showed no deficits in learning and later recognizing new scenes."
A study looked at memory performance in 140 patients who had undergone an operation called an amygdalohippocampectomy, which removes both the hippocampus and the amygdala. Table 1 of the study found that such an operation had no significant effect on nonverbal memory, causing a difference of less than 3%. Table 3 shows that most patients were unchanged in their verbal memory and nonverbal memory. More patients had a loss in memory than a gain, although about 13% had a gain in nonverbal memory. These results are not at all consistent with Burnett's claim that "the hippocampus links all of the relevant information together and encodes it into a new memory by forming new synapses."
There is a reason why it cannot be true that a new memory requires a formation of new synapses. The reason is that humans can form new memories instantly, but both the formation of a new synapse and the strengthening of a synapse require minutes of time. If someone fires a bullet that passes near your head, you will instantly form a permanent new memory that you will remember the rest of your life. The same thing will happen the moment you break your leg in a biking accident. Claiming that memories require either the formation of new synapses or the strengthening of synapses is incompatible with a fact of human experience, that humans can form new memories instantly.
In this experiment, pairs like those shown below were used. A subject might be presented for 3 seconds with one of the two images in the pair, and then hours later be shown both images in the pair, and be asked which of the two was the one he saw.
There is another reason why it cannot be true that we remember things because "the hippocampus links all of the relevant information together and encodes it into a new memory by forming new synapses," as Burnett claims. The reason is that synapses are too unstable to be a storage place for memories that can last for decades. The proteins in synapses have short lifetimes, lasting for an average of no more than about two weeks.
A fairly recent paper on the lifetime of synapse proteins is 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 less than 20 days. The synapses themselves do not last for more than a few years. So synapses lack the stability that would have to exist if memories are to be stored for years. Humans can reliably remember things for more than 50 years. Such a length of time is about 1000 times longer than the lifetime of proteins in synapses.
Without providing any evidence for such a claim, Burnett teaches the widely taught idea that memories migrate from one part of the brain to another. He states the following:
"Newer memories, once consolidated, appear to reside in the hippocampus for a while. But as more memories are formed, the neurons that represent a specific memory migrate further into the cortex."
We have no understanding of how a neuron could represent a memory, no evidence that memories are written to any part of the brain, and no understanding of how any such thing as a writing of a memory could occur in neurons and synapses. We also have zero understanding of how a written memory could migrate from one place in a brain to another place, nor do we have any direct evidence that any such migration occurs. But we do have an extremely strong reason for thinking that accurate memories could not possibly migrate from a hippocampus into the cortex. The reason has to do with the very low reliability of signal transmission in the cortex.
A scientific paper 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."





