I recently discovered a web site called The Transmitter (www.thetransmitter.org) that mainly covers neuroscience research and neuroscience theory. When read in a critical manner, an article on the last site serves to powerfully remind us that neuroscientists lack any such thing as either a real theory of memory storage or a real theory of life-long memory persistence. When scientists speak on these topics, they offer only the flimsiest catchphrases, soundbites that have the weight of soap bubbles.
The title of the article is "What makes memories last—dynamic ensembles or static synapses?" The reference to "static synapses" is a very misleading one. Everything we know about synapses tells us that a synapse is an unstable thing that cannot last for years.
"The debate over how information is stored in the brain is often represented as one between two extremes. One viewpoint posits that learning induces changes in gene expression that ultimately alter the structure and function of specific synapses within the physical memory circuit, or engram. These molecular changes at the synapses can remain stable for the lifetime of the memory. The other viewpoint claims that information is represented not in a specific set of cells or synapses but rather across a loose set of cells and circuits that 'drift' over time."
The narrative of two rival theories is a false one. The situation is really "no theory at all" but merely empty, vacuous sound bites and slogans such as "synapse strengthening," which may differ from one speaker to the next. The claim above that "molecular changes at the synapses can remain stable for the lifetime of the memory" is something entirely contrary to fact. We know that human memories can persist for more than 50 years. Synapses, on the other hand, are "shifting sands" type of things that are dramatically unstable. The proteins that make up synapses have an average lifetime of less than 3 weeks. Synapses are connected to dendritic spines, which are known to have short lifetimes, not lasting for years. Remarkably synapses are built of proteins which have an average lifetime about 1000 times shorter than the maximum length of time that humans can remember things. This discrepancy is one of very many reasons why the idea that memories are stored in synapses is one of the most nonsensical ideas that scientists have ever advanced.
Notice well the utter emptiness of what is discussed as an alternative to the utterly-vacuous-by-itself idea that memories are formed by "synapse strengthening." The alternative is presented as the idea that " information is represented not in a specific set of cells or synapses but rather across a loose set of cells and circuits that 'drift' over time." That's an utterly vague, vacuous, empty sound bite that is as much of an empty soap bubble as the equally empty notion of "synapse strengthening." Not the slightest bit of weight is added by the next two sentences:
"In this view, the cells that initially encoded an experience are not the same set of cells that actually store the information. Indeed, the precise set of cells do not matter in this framework—the information for a specific memory is instead decoded from the computational space of firing patterns across a set of cells."
As some type of attempt to explain stable memories that can last for 50 years, this idea is as supremely goofy as the idea that memories that last for 50 years are stored in the "shifting sands" of synapses. The "firing patterns" in the brain are ever-changing. Trying to claim that stable memories are stored in "firing patterns" is as goofy as the claim that your tax records and childhood photos are stored in the wind patterns around your house.
Shepherd gives us some "rival cases" paragraphs. Under a heading of "The case for memory engrams," he makes some untrue statements. He states this:
" In experiments that used this approach, light-sensitive receptors were expressed only in the cells active during learning. Shining a light to activate these cells days or even weeks after training resulted in the recall of a memory without any external experience or cue. This remarkable observation set the stage for the idea that 'engram' neurons that encode learning are sufficient to store and recall a memory."
No robust research of any such type ever occurred. Shepherd is simply repeating a groundless achievement legend of neuroscientists. When you read the papers that claim to have done such things, you will always find that they were junk-science studies guilty of multiple types of Questionable Research Practices such as the use of way-too-small study group sizes, and the use of unreliable techniques for attempting to judge recall in rodents: the unreliable method of trying to judge "freezing behavior."
Under the heading of "the representational drift perspective," Shepherd presents nothing in the way of any evidence. We get only the most roundabout hand-waving.
Shepherd then asks eight neuroscientists for their opinions on the topic of memory storage by a brain. Shepherd follows a senseless procedure. A good open question to ask would be something like this:
"Do you have a good, credible theory of how a brain could store memories, and how memories could persist a lifetime? If so, describe the best evidence for such a theory, and tell us how confident you are that such a theory is true."
And a good follow-up question would be questions like this:
- "Are there any physical factors in the brain that argue against such a theory? Explain how such a theory could really allow 50-year memory storage despite all the molecular and structural turnover in the brain."
- "Trying to be precise, and avoiding vague language, can you explain exactly how a detailed memory could be stored under such a theory? For example, exactly how could a brain store a page of text that someone had memorized, so that the person could retrieve that whole page?"
- "Under such a theory, how would it be possible for someone to instantly recall lots of relevant detailed information after seeing a single face or hearing a single name? For example, how could someone ever recite a paragraph describing the life of Abraham Lincoln after merely hearing his name? How could information about Lincoln stored in a brain ever be found quickly enough to allow instant recall?"
But Shepherd asks no such challenging questions to his eight neuroscientists. Instead he asks each of them the softest of softball questions. Each neuroscientist is asked these questions:
- "Is information stored in the brain at the level of cells (or circuits) or at the level of synapses?"
- "Can we reconcile observations that show distinct engram circuits seem to store memories versus observations that show the neuronal activity of these memory engram drifts?"
- "What experimental data would be helpful to reconcile these observations to help bring these theories together?"
- Andre Fenton of New York University has nothing of any substance to say. He says "information is not stored in any single element," and "it may not be practically possible to separate the process of storage from the access," both of which suggest that he has no understanding of how a brain could store a memory. People who understand how some type of information is stored do not say such things.
- Loren Frank of the University of California gives us no impression that he understands how a brain could store a memory. He says, "It might be that changes in gene expression lead to changes in activity levels, although at the moment we really don’t understand the scope of these changes." He offers only the vaguest hand-waving, with a mention of the hippocampus. We have an example of the vaguest and most conceptually empty hand-waving in this statement by Frank: "Focusing on memories for the events of daily life, our current conception is that the events themselves drive activity across the brain, engaging specific neurons whose activity represents the various sights, sounds, smells and feelings that are part of the experience."
- Kari Hoffman of Vanderbilt University also offers only the vaguest handwaving, an example being this statement: "I would submit that much of the heavy lifting is done at both the synaptic and circuit/ensemble level. Which levels dominate depends on factors such as memory type, when information was acquired and how it is integrated with the existing structures, themselves reflecting changes from earlier experiences. " Another statement by her indicates she has no real understanding on this topic: "That said, we may need to be careful in using the term 'these memories' or 'these memory engrams.' Such terms suggest that experience creates biological bins to hold discrete memories, that memories exist as entities that are created 'de novo,' and that neural modifications must reside at only one level, all of which are positions that are not or may not be true."
- Yingxi Lin of the University of Texas says, "It is, however, too early to say that those cells and synapses are sites of stored memory per se, as they may simply function to gain access to the memory." She also says, " It is also possible that there aren’t specific sites for memory storage; cells and synapses may be part of a brain-wide code for memory expression." She seems to have no understanding of how a brain could store a memory.
- Cian O'Donnell of Ulster University sounds like a weak scholar of neuroscience when he states, "The field has held synaptic plasticity up as the main mechanism for information storage in the brain for several decades now, and I haven’t heard any good reasons to start doubting it yet." There are very many such reasons, such as the fact that synapses are composed of proteins with very short lifetimes, the fact that synapses bear no resemblance to any system for writing or reading information, the fact that synapses do not reliably transmit information, and that synapses are connected to dendritic spines that are unstable and do not last for years. Nothing O'Donnell says makes him sound like anyone with an understanding of how a brain could store memories.
- Timothy O'Leary of Cambridge University (not to be confused with the late Timothy Leary of Harvard) says nothing to inspire any confidence that he has any understanding of how a brain could store a memory. All he does is to reveal that he fell "hook, line and sinker" for bad neuroscience experiments using way-too-small study group sizes and the utterly unreliable technique of trying to judge recall by judging "freezing behavior."
- Tomas Ryan of Trinity College also says says nothing to inspire any confidence that he has any understanding of how a brain could store a memory. He engages in the emptiest of hand-waving when he says this: "It seems to me that the plausible level for the storage of long-term memories is in the topography of the connectome. So, the information is engraved through stable changes in the brain’s microanatomical circuit." The "connectome" he refers to is the collection of all synapses. But synapses are not stable, but the opposite of stable. So his claim makes no sense.
- The last of the eight neuroscientists is Evan Schaffer of the School of Medicine at Mount Sinai. He states this: "As a consequence, I don’t think information can be stored in cells or synapses in the hippocampus in a way that is stable over a lifetime. In other parts of the brain, this may not be the case." No, actually, there is no credible storage place for memories in the brain, either in the hippocampus or anywhere else. Not sounding like anyone who understands how a brain could store memories, Schaffer also sounds like a very bad student of human mental performance. Most misleadingly, he tries to suggest that humans may not be able to remember things for weeks. He says, "On a timescale of a few days, memories seem pretty stable. On a timescale of a few weeks, there’s less evidence for stability." To the contrary, there is abundant evidence that humans can very well remember things for decades.
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