Volatility of Human Memory

prostoalex writes "Scientific Americans looks into the human brain, trying to figure out why some events just tend to stick in our memories forever, while the others are gone: "How does a gene "know" when to strengthen a synapse permanently and when to let a fleeting moment fade unrecorded? And how do the proteins encoded by the gene "know" which of thousands of synapses to strengthen? The same questions have implications for understanding fetal brain development, a time when the brain is deciding which synaptic connections to keep and which to discard. In studying that phenomenon, my lab came up with an intriguing solution to one of these mysteries of memory.""

Comments

This is kinda interesting

[gtrubetskoy]

From the recently noted on slashdot Edge poll What do You believe is true even though you cannot prove it, I remember this bit by Terrence Sejnowski caught my attention (I'm pasting it here cause I can't figure out how to link to that specific part of the page):

How do we remember the past? There are many answers to this question, depending on whether you are an historian, artist or scientist. As a scientist I have wanted to know where in the brain memories are stored and how they are storedthe genetic and neural mechanisms. Although neuroscientists have made tremendous progress in uncovering neural mechanisms for learning, I believe, but cannot prove, that we are all looking in the wrong place for long-term memory.

I have been puzzled by my ability to remember my childhood, despite the fact that most of the molecules in my body today are not the same ones I had as a childin particular, the molecules that make up my brain are constantly turning over, being replaced with newly minted molecules. Perhaps memories only seem to be stable. Rehearsal strengthens memories, and can even alter them. However, I have detailed memories of specific places where I lived 50 years ago that I doubt I ever rehearsed but can be easily verified, so the stability of long-term memories is a real problem.

Textbooks in neuroscience, including one that I coauthored, say that memories are stored at synapses between neurons in the brain, of which there are many. In neural network models of memory, information can be stored by selectively altering the strengths of the synapses, and "spike-time dependent plasticity" at synapses in the cerebral cortex has been found with these properties. This is a hot area of research, but all we need to know here is that patterns of neural activity can indeed modify a lot of molecular machinery inside a neuron.

If memories are stored as changes to molecules inside cells, which are constantly being replaced, how can a memory remain stable over 50 years? My hunch is that everyone is looking in the wrong place: that the substrate of really old memories is located not inside cells, but outside cells, in the extracellular space. The space between cells is not empty, but filled with a matrix of tough material that is difficult to dissolve and turns over very slowly if at all. The extracellular matrix connects cells and maintains the shape of the cell mass. This is why scars on your body haven't changed much after decades of slougare contained in the endoskeleton that connects cells to each other. The intracellular machinery holds memories temporarily and decides what to permanently store in the matrix, perhaps while you are sleeping. It might be possible someday to stain this memory endoskeleton and see what memories look like.what makes you a unique individualhing off skin cells.

My intuition is based on a set of classic experiments on the neuromuscular junction between a motor neuron and a muscle cell, a giant synapse that activates the muscle. The specialized extracellular matrix at the neuromuscular junction, called the basal lamina, consists of proteoglycans, glycoproteins, including collagen, and adhesion molecules such as laminin and fibronectin. If the nerve that activates a muscle is crushed, the nerve fiber grows back to the junction and forms a specialized nerve terminal ending. This occurs even if the muscle cell is also killed. The memory of the contact is preserved by the basal lamina at the junction. Similar material exists at synapses in the brain, which could permanently maintain overall connectivity despite the coming and going of molecules inside neurons.

How could we prove that the extracellular matrix really is responsible for long-term memories? One way to disprove it would be to disrupt the extracellular matrix and see if the memories remain. This can be done with enzymes or by knocking out one or more key molecules with techniques from molecular genetics. If I am right, then all of your memories

Re:This is kinda interesting

[FleaPlus]

That's bullshit.

I wouldn't be so quick to dismiss it. Terry Sejnowski is probably one of the most prominent neuroscientists alive today, and generally knows what he's talking about.

You do not need constancy of material/molecules to keep a memory - in a sense you can exchange a building brick by brick, one at a time, with new bricks, and maintain your building like new, for millenia.

This is true, and undoubtedly works well for short-term and medium-term memories. However, all of this exchange takes energy, and if there's a more energy efficient way of doing things (such as, perhaps, storing memories in the extracellular matrix), evolution would tend to select in favor of it.

Re:This is kinda interesting

[nucal]

The idea that the extracellular matrix might control neuron plasticity is not all that far fetched - there are many studies showing that cell function is controlled by the extracellular environment.

Another aspect to consider is that diseases such as Alzheimers are associated with the accumulation of misfolded proteins (plaques) in the extracellular environment. Although the prevailing idea is that these plaques might be toxic or the residue of dead cells, it's not impossible to think that plaques could also "de-program" neurons by altering the normal extracellular environment.

Re:This is kinda interesting

[Tlosk]

While I belive Sejnowski is absolutely correct that there's probably a lot worth investigating in the extracellular material, one possibility is that very long term memories are illusory.

Rarely are these long term memories of the same quality as very recent memories, and I don't just mean of strength, but that they are qualitatively different. That you no longer have access to what one might call witness memory, where if someone asks you questions about the event you can search the myriad details of the event to find the answer.

Given that the bulk of our early memories are lost over time, what's special about that handful of memories that we do hold onto and that are veridical? I suspect that most of this subset of retained memories are not the original memories but rather memories of the memories.

Personally, when I go over the longest memories I still hold onto, they are almost all experiences that I at some point either told someone else about, thought about, or had cause to remember at some point in the past. Each time you do this the memory is copied to other areas (whatever those might be, we still don't have a good grasp on this). And most of a given memory that I now have owes its features to the nature of the account I gave earlier.

For example say someone remembers the experience of riding on their grandmother's lap on a train when he goes to visit her at the age of three. Shortly after that he will have all sorts of specific stored information relating to that particular event. If the event is never revisited it will likely be almost entirely lost, but if several years later he tells someone else about the experience, a memory of the event recounted still many years further down the road would depend heavily on what exactly the person shared during that earlier recounting. That is, the person is no longer remembering the event, but rather recalling the earlier recounting.

Oh if you're cued well enough you can remember all sorts of things from way back, but they are so fragmentary that it's probably just the distributed nature of memory that saves them from complete loss most of the time. There will always be a few bits and pieces floating around in there.

Pain for me

[purduephotog]

I remember back to when I was only 2 years old- I had had surgery on ... well, we'll call it a sensitive part of the body.

Now I don't remember the surgery, and I don't remember the antics I pulled at showing nurses why I was in the hospital... but I *do* remember the first time I had to goto the bathroom after surgery.

That memory is so seared into my brain I can even recall I was high enough to look out a window over the cityscape, and that there was a bricked church in the background and the window had blinds (the black slatted ones) on it.

And I remember so much so terribly much pain I don't know how I survived it.

My parents tell me that after that brief moment of screaming I was OK... and I don't remember anything else of that event save for that moment.

And just for comparison (of a little kid) I've had 18 kidney stones... I have a good memory for pain. But that memory makes me cringe and shiver every time I have it.

Re:Pain for me

[softparade]

While my grandfather was going through some old rubbish in the garage he found an old photo album that was my dads. In the album are photos of my Dad while in Vietnam. When we showed it to him he couldn't remember who made the album or many of the people in the photos. Given it was more than 30 years ago, but its weird how such events can be forgotten.

Re:Pain for me

[rbarreira]

Pain usually wants to be forgotten by the brain... And everyone is different, which might explain why your dad "forgot" (I'm sure he knows it deep inside even if he thinks he doesn't), and the grand-parent poster remembers his experience.

Re:Pain for me

[MBCook]

That's true, and I've heard it before. Many people remember traumatic events, and they remember that they WERE in pain, but they often don't remember the pain, or despite it's severity they don't "expiriance it" when they remember it.

This is very often true of pregnancy. I've been told (being a 21 year old guy, I'll never really know) that while childbirth is painful for humans (duh), women don't tend to remember it after childbirth. This is supposedly a genetic trait becuase otherwise women wouldn't be likely to have a second child, which could be bad for our species.

Memory is facinating.

Re:Pain for me

[elbobo]

I'm not sure I'm understanding you right. You're saying you think there's no such thing as repressed memories? I can't see that anyone could argue such a thing in the face of all the counter evidence.

I, for one, know for absolute certain that repressed memories exist. I suffered a very traumatic and gory accident when I was 13. I have vivid memories of the details right up to and right after the event, but have absolutely no memory of the moment of the accident. I know for certain that I would have seen it with my eyes, and would have felt it, but yet I have no recollection of seeing it or feeling it.

I can reasonably safely assume that I had recollection of the event immediately afterwards, as I recall immediately looking to the part of my body where it happened. So my mind must have blanked the event out sometime shortly after that.

Repressed memories exist. I imagine it's to do with the mind blocking out events which are so traumatic that we wouldn't be able to cope with reliving them in thought.

Oh, for the record, my accident was having one of my legs sliced repeatedly by a boat propeller. It's the kind of thing you'd think you'd remember.

Re:Pain for me

[Pooua]

I, for one, know for absolute certain that repressed memories exist.

By way of introduction, I am not so certain.

I suffered a very traumatic and gory accident when I was 13.

I have experienced several intense, painful and traumatic accidents.

I have vivid memories of the details right up to and right after the event, but have absolutely no memory of the moment of the accident.

Do you remember a loud noise, which seemed to drown out everything around you?

I know for certain that I would have seen it with my eyes, and would have felt it, but yet I have no recollection of seeing it or feeling it.

It is likely you would have been looking at it. You might not have felt it, as pain takes some time to set in, especially if it is extreme pain. You may not have had enough time to have felt the event as it happened (sensory overload).

I can reasonably safely assume that I had recollection of the event immediately afterwards, as I recall immediately looking to the part of my body where it happened.

So you knew about the event, but can we be certain that you were conscious of the event as it happened? I don't believe that would be the case. I say this, based on my own experiences with sensory overload. Suppose that at the same time that this event was happening to you, your emotional state was sending very strong signals to your brain. It is possible that your emotions would swamp the other signals. You would lose the information in a white out.

So my mind must have blanked the event out sometime shortly after that.

I speculate that you only had a short-term memory of the event, which rapidly faded.

Repressed memories exist. I imagine it's to do with the mind blocking out events which are so traumatic that we wouldn't be able to cope with reliving them in thought.

If your memory were repressed, it would be a memory that something is inhibiting. My theory is that whatever memory you might have of the event is only a very weak signal, because your awareness of the event was limited, and hardly recorded.

Oh, for the record, my accident was having one of my legs sliced repeatedly by a boat propeller. It's the kind of thing you'd think you'd remember.

I think it depends on your state of mind at the time.

When I was about 15 years old, I was riding a moped down the right-hand side of a highway out in the country. I decided that I had to make a left turn ahead of some approaching traffic. As I made the turn, I heard car tires screeching on pavement behind me. I knew what was happening. I remember hearing the pitch of the screeching drop, as if the tires were sliding through gravel, instead of on pavement. I attribute this to a change in my sense of time (this has happened to me on several other occassions, particularly when I am in danger). I remember many little details from that point that could not have taken more than a few milliseconds to transpire. I looked down, and saw the front of the car (travelling somewhere around 40 mph by then) about 3 feet from my left leg. I was able to look up, plan a course of evasive action, and begin to tighten the muscles in my right arm as I attempted to turn the steering handles of the moped. I remember the muscles in my arm tightening. Then, I found myself in another world. I have three memories of what happened, but they are all like a dream-state or an alternate universe. In two of the dreams, I was aware of my body being in mid-air on its back. In one dream, I actually looked at my body floating in the air, as I watched it from the side of the road. According to a witness, I was unconcious for about 15 minutes, following my landing on the hood of the car as it continued across to the far side of the highway. When I awoke, I was standing on the ground on the other side of the highway from where I had been when I was struck by the car, across 3 lanes. Through all that, I was doing my best to stay mentally

Does this shed any more light on coding solutions?

[Sowelu]

I've been tracking the periphery of AI for quite a while. Even though directly emulating the human brain is probably not the best solution for artificial intelligence, has this research opened any new doors lately?

Fake memories

[D H NG]

Sometimes our brains can be tricked into remembering things that did not happen. Elizabeth Loftus had done much research in the area of misinformation effect, which actually has legal repercussions.

Re:Fake memories

[Nutty_Irishman]

There is an interesting memory approach called Image streaming that deals with conjuring memories that you didn't think ever happened. The odd thing about it is that many times the things you forgot actually get remembered(and not fake memories). It makes one wonder if indeed we actually ever forgotten them at all or just misplaced them.

http://www.geocities.com/Athens/Forum/6243/imstri. html

You can laugh and not believe it at all, but Image Streaming is remarkeably effective in remembering events you think you had forgoten. For you can start with an old childhood memory of a person but not remember exactly what they looked like. After a period of time streaming and describing what they looked like you can build up the image of the person that you thought you had forgotten. It's like putting together the peices of a jigsaw-puzzle. You start off with a little bit, but you slowly add peices to the puzzle. As time goes on and you see more of the puzzle you find peices that you thought you lost. Eventually, you get to see the whole puzzle.

It is also quite effective in creativity and random guessing. I was actually quite suprised at how much easier it is for me to come up with ideas or solutions that I would never have thought of before. Once you really get into it you'd be suprised how effective it actually is, and following the mental progression of images to some solution is quite remarkeable. If you don't believe me, check your local library and pick up the book and read the first few chapters. Try it for a week or two, and if you still don't believe it put it down. I bought the book more for shits and giggles between undergrad and grad but was quite suprised with the results and my creativity afterwards.

or, 'Potential Programmability of Human Memory'

[brian.glanz]

A leitmotif the article turns on is the potential programmability, more than the volatility, of human memory. They discuss how the older view of our memory as volatile and mysterious has been refined, as we've discovered the mechanisms for transition between short and long term memory. From the physiological to the cellular level, the idea here is a familiar one -- we know more than ever, and we're learning faster than we had before, in this case about memory and about learning.

Most intriguing are the material implications of the article -- they find memories transitioning to long term storage when information is reinforced at specific intervals and with specific techniques. This matches some experimental evidence as referred to, like the familiar ideas of studying or preparing in the same location you will test or perform in -- but, its level of specificity begs for more experimentation and refinement of memory management techniques. Learning and memory across the whole human experience can be biologically maximized if we find just the right process -- read that slippery section in x minute increments and take 10 minute brakes between 3 repetitions. Or maybe, do asdf to remember x words by rote for the next 4 hours, and do ;lkj to sufficiently remember x for a month. Without running a cord into your ear, the article is promising for its level of detail in exact ways we might approach finding best practices for our current hardware.

I'm curious generally about how soon articles like this, especially up at the Scientific American level of exposure, translate into experiments at universities (and, self-help books?). I'm tempted to modify my own learning accordingly, n/m waiting.

BG

Re:Data storage

[laughingcoyote]

However, there seems to be another difference...

Data on a hard drive, until the hard drive -does- begin to malfunction, is stored perfectly. That is, if I type a paragraph (or an entire book), save it, come back a year later, and reopen that file, then provided that the hard drive is functioning properly, that book will be pulled right back up, word-for-word. While the brain might remember the -idea- of the book, then chances are, if you are asked to repeat, word for word, the third paragraph on page 287, you will not be able to do so, even five minutes after reading it.

Of course, the ability to condense, interpret, and distill the important points out of information is what makes humans superior to computers. But there's something to be said for having a medium (paper and pen, computer, camera, whatever) that can store something exactly, and pull it up to refresh your memory (which likely still has the outline and highlights of important subjects, but may be missing the details) when the need be.

Also, whatever the brain may do, it doesn't always seem to work flawlessly at distinguishing important from unimportant. I have quite a few things pop into my head, at various times, some from when I was as young as 2. These things weren't really important to me even then, and sure in the hell aren't now. But they stay around. Now on the other hand, I'm sure my boss told me to do something, but I just can't remember what it might've been...

Re:Catch 22

[nEoN nOoDlE]

Call me crazy, but I'd love to have the ability to remember every license plate number and commercial order on tv. Some people already have such photographic memories (to some extent). I think even with the capacity to recall every little detail, doesn't mean that the big details will go into the background. We will still have the ability to categorize those memories as we do now, but instead of the small ones getting lost in the ether, we will be able to recall them at will. I think if the contents of everything we've ever read and done is logged permanently in our brain for easy recollection, we would be infinitely more intelligent, and would be able to link concepts that we've read about years ago with newly learned ones with a lot greater ease.

Is there anything new here?

[Glowing Fish]

This article is a rehash of basic neuronal theory (known for at least a 100 years ago), and slightly less basic information on Long Term Potentiation (which has been known about since the early 70s, although they have been discovering more in recent years); followed by some guesses at how the calcium influx triggers genetic change, because "genetics" is the trendy branch of Biology that is familiar from the cover of Time.

What we don't know is where and how Long Term memories are stored. We know that they are formed through synaptic input in the limbic system. Presumably, they are then passed to somewhere in the cortex. Why? How? Where? That is what we don't know.

BTW, it is quite easy to do your own experiments on LTP. Although they can be a bit dangerous.

Re:Yes interesting indeed!

[Stuart Poss]

A point of the original article and known from
various studies in neuroscience is that "memory" and "mental activity" can not be fully distinguished from the "architecture" of the nerves themselves. Neurons are connected via synapses on dendrites and connections are being formed and reshaped (new topologies of interconnectness. Thus, as differential activity ensues, differential connectedness and synapse development occurs concomitantly. Some neuronal paths will be selected for, while others will be selected against. Hence, "memories" may be stored as "architecture" as well as by the multiple biochemical pathways modulating the formation and "strength" of different "circuits" that ultimately "add" or "multiply" the effect of the firing patterns on the genetic machinery in the nucleus of the neuron, which are critical to the maintenance of longterm memory. It may be a fundamental mistake to assume that "memories" are individual molecules, even though many molecules ultimately are ultimately involved in their existence.

The article is interesting in that the neuron may in some respects by acting like an antenna, whose cellular/genetic machinery and morphology (architecture of dendrites and synapse topology) are designed to adaptively differentially "tune" for different action potential input/output logic via differential signal strength from relative importance of different connections, different dendrite size, and different numbers of synapses.

Perhaps this may suggest that the path to wisdom is to be found by becoming a much better "listener". Attention to subtle nuance may be far more important than our current political culture admits.

This might also go a long way towards explaining why different species have such different brains, yet brains whose underlying organization is so similar.

Imperfect memory? Yes, please...

[Reteo Varala]

Personally, I'd prefer a volatile memory.

There are some good things about a clear memory. Being able to recall things with a minimal amount of effort, and maybe, if it's stubborn, the easy recall of where to find it. Immediate notice of a flaw in a pattern, no matter how miniscule or unnoticeable. Noticing inconsistency in a conversation. Tracking how much money you have left.

However, it does have it's downside.

Ever hear the saying "Someday we'll look back and laugh at this?"

I'm still waiting. I still cringe over every single embarassing memory in the 30-year period that is my life. Those memories, when I recall them, are much too clear, and it feels like it just happened, despite the fact that some of those events had occurred over 20-25 years ago. Sometimes it's so strong, I feel the need to shut down, and lately, it's started to cause nervous reactions; too many things are drawing them up as I work to re-integrate myself into that thing known as "Humanity."

Thankfully, my memory, while vivid, is still selective, and I can find the mercy of forgetfulness. I don't think I could survive a photographic memory with my sanity intact.

It is said that if you recalled every single thing, it would take a strong will not to go mad. I believe it.

Memory vs. Memories

[Couzin2000]

It's interesting to read the point of view of others. That generally is the way for us to form opinions, and, well, I have my own opinion formed.

I think it's probably not so much a matter of "strengthening" a synapse to remember more clearly. I think it's more of an associative memory thing. As we all know, remembering certain things are "triggered" by events, occurences and coincidences. Certain things could be remembered during a conversation on a certain topic, for example; haven't we all played that game where someone says how bad a fall they took from their bike when that someone was young, and then we go on to say "Well, check out the fall I took..." and then go on to tell them an even worse fall? I think it's things we see, hear, taste, smell, touch, that trigger these memories into surfacing.

Part of this is associative, and we all do it. But, some events are almost omnipresent in our minds. For example, a rape victim. The victim will remember this event on the premise that so many times she's heard about how bad that could be, how intolerable a behaviour that could be for a human, and we get it drilled in our minds. When the event actually happens to her, it will trigger all these memories of hearing how bad it is all at once.

The reverse will then happen: anytime a rape victim will see a commercial on rape prevention, or a attempted rape scene in a movie, that will in turn trigger all these times that she was told that rape is bad, and the event itself. (Keep in mind here, I'm in no way saying rape is just an "event" - I do NOT condone it. We're just not discussing the moral implications here.)

Associations are made between memories and, in turn, synapses, because of all the possible interconnections they have. Based on all the similarities or closeness of incidents in our lives, we re-associate events that happen daily to old, pushed-away-to-the-side memories. That's how when you see an old friend you haven't seen in so long can "bring back" so many great memories.. and bad ones as well.

I doubt that certain events are more powerful than others, but I think they might be more potent than some, simply by all these things we associate together.

My 2 cents!

Mental heart-beat

[jedwardsnz]

In light of this article, perhaps the following mental discipline may be useful:

Every ten minutes, review the important experiences of the preceding ten minutes. Also review the important events of the preceding couple of ten-minute intervals.

I guess this would be like a 'mental heart-beat', that would serve to keep your mind active and your useful memories intact.

Witness discreditation program

[ynotds]

This kind of research is slowly undermining the legal fiction of eye witness testimony.

If in order to commit something to long term memory you need to reactivate relevant synapses after an interval measured in minutes, then the reactivation will surely be compromised by whatever rationalisation you have managed to do in the interim.

If I recall correctly, there have been controlled experiments done in which a stooge managed to readily convince witnesses that certain details of an event where quite different to what had actually happened.

My brain without me.

[cabazorro]

My project wound down in October. Since then I've been doing documentation and non-programming duties.

Yesterday I had to add a line to a file.
A simple unix command that a few months ago I could have spitted out like second nature...

was gone!

I walked aimlessly through the cube-maze string at blank faces trying to remember but I couldn't.

Was that a cat command? set? awk?

I asked some gurus and referred my to the >> command. Than I sat back in front of my white board and gently and swiftly the line emerged from my dry marker.

>echo "my line" >> myFile

Panick receded and was replaced with cautious optimism.

The understand the nature of volatile memory one has to read ./ for a few months, fall in Love or perhaps read Thomas Mann "Magic Mountain".