[dentstudent (OP)]

I know that I was making a hot beverage at the time, in either 2 or 3 cups. I know that my girlfriend at the time and her mother were in the room next to the hallway and that I took one cup from my left hand with my right to place it on the table in the middle of the room. What colours the cups were, whether it was tea or coffee, what kind of table it was, what they were wearing, pass. No idea. Perhaps these are the bits of the memory that the brain "decides" to lose, as they are peripheral to the memory, and not important as such.

The dogs name was "Sammy". But as you say, this bit isn't important, as I must have known that already. But, how do I suddenly remember it? What is it that suddenly enables me to recall that piece of information, when 10 minutes ago, I couldn't?

[Karen W.]

You have have probably seen or done something in the period of time that either caught your eye visually or triggered a memory.. There are things in my past that I blocked that have been triggered by something as silly  as seeing my husband removed the belt from his pants... or to see someone use a riding crop on a horse..

every time I see something spin.. my mind immediately remembers a silly toy my daughter had when she was 2 or three weeks old...not even old enough to play with it! LOL... silly things like the color of something or a smell hitting my nose just right! It is weird how that works!

[another_someone]

OK, I will try and explain my understanding about how memory works, but I will stress that this is my own conjecture based on my observations, and not anything authoritative.

Firstly, memory obviously comes in many forms.

The most persistent type of memory is very crude and limited.  This is deeply learnt memory, either learnt by extreme repetition (particularly in early life) or by deep emotional trauma.  It is the kind of memory that, even when we have a very deep amnesia, will probably still allow us to talk in our native tongue.  It is the kind of memory that will allow a pianist who has amnesia to still play the piano, even if he may not necessarily know the names of the pieces of music he is playing, nor visualise the music, but his hands know where they must go, although he may not know why they should go there.  In the most extreme case, I suspect it is also related to the nature of addiction, since addiction too will make permanent changes to one's brain that will remain in place even if one has total amnesia about every fact of one's everyday life.  To a lesser extent, it also I suspect explains how I can sometimes travel along a road that I have not travelled in for many years, and have totally forgotten the route I should take, yet at each turning, I know which way I should turn, even though I cannot visualise the next turning I need to take until I have actually got there, see the junction, and then instinctively know whether I should turn left or should turn right.

At the opposite end of the spectrum we have sensory input, and I don't actually believe that sensory input is stored for more than the most transient time (hence why I don't believe that people have true photographic memories – although different people may remember more or less of the factual information within an image, it is still not the image itself that they remember).  When one closes one's eyes, and imagines some memory from the past, I don't believe you actually recall the images of the past so much as reconstruct the images from factual information that you stored pertaining to the image.  One example of this reconstruction of sensory information is in dreams.  An example of this is where a friend of mine recounted a dream she had where she was living in Roman Briton, and overheard some centurions speaking in Latin, and despite the fact that her knowledge of Latin was of a few Latin classes in school some almost  6 decades earlier, and she clearly could not have had the skills to understand complex conversational Latin, yet she was able to understand every word the centurions were speaking.  Clearly, this was nonsense; not least because, within her dreams, she could not have heard anything – her sensory perceptions could not have been associated with any sounds she heard then, or at any time in the past.  The only sensible explanation is that she created the facts of the meanings of the words she heard, and she, in her dream, created the fact that the language spoken was Latin, and then she tried to backfill the sensory information to match the facts that she believed she knew.  I believe the same is true of your memory of being bitten by the dog.  I do not believe you have any sensory memory of that incident, for if you do have a true visual recollection of the incident, it cannot be explained how you can remember that your mother and girlfriend were present, yet you do not recollect such components of the same visual image as anything pertaining to the clothing they were wearing.  Rather, you remember many facts of the incident, but the only way you are able to verbalise those facts is by trying to reconstruct a visual image by backfilling sensory information from the abstract facts that you recall.

As for the question about how we remember, and how we forget, and the boundary between them.  I believe the brain, aside from the habitually learned information that I started this post with, is mostly a very forgetful machine.  Facts that we learn every day we forget very, very quickly.  In order for the brain to remember information for any period of time, it has to keep constantly copying that information.  Every time you access a piece of information, you make a copy of that information (and incidentally make a copy of information that is closely related to that information).  Thus, if you keep copying information faster than you are forgetting information, then you will build up more and more copies of that information.  Once you cease to access the information regularly, and so cease to make regular copies of the information, the rate at which you lose the memories of the information will begin to exceed the rate at which new copies of that information is made.

We also know that the brain has both short term, and long term, memory.  I suspect there are many nuances between, where some memory in also in intermediate, and some memory is in very long term (the most extreme being the habitual memory where we have burnt in habitual motor skills, language skills, etc.).  How quickly memory can be accessed (in a totally random fashion – this is different if one is accessing memory sequentially, where the context of a previous recollection makes it easy to access something close by) depends on the size of the memory storage it is accessing.  Shorter term memory has a smaller capacity, so access to information within it is faster.  This shorter term memory relates to most recent events, and so is quick to be laid down, and quick to forget.  Nonetheless, memories within the shorter term memory that are heavily duplicated will be copied to longer (intermediate) term memories before they are lost from the shorter term memories (although I am expressing this as if a single piece of fact is moved from one storage to another, I don't actually believe that facts are discrete units, which is why one also copies some associated memories with the primary memory – it is more like each level of memory has a fuzzy image of a set of facts, and as time progresses, as long as the memory is actively being accessed, then the fuzziness gets ever more in sharper focus, but as the memory atrophies, so it becomes ever fuzzier again).  One has to bear in mind (if you'll pardon the pun) that the brain is a neural network, rather than a database engine; so is more like a hologram than a photograph (i.e. if you have a high definition photograph or two people standing next to each other, then if you cut that photograph in two, you then have a high definition photograph of one person; while, because each point on the hologram contains some information about every part of the image, if that same image is recorded on a hologram, and you cut that hologram in half, rather than being left with a high definition photograph on one person, you are left with a low definition hologram of two people).

As to why it sometimes takes a long time to access some old memories; I suspect that after having searched its recent memories, and failed to find the information it is looking for, the brain then goes about trying to construct lots of different keys with which it might be able to locate the information in the longer term storage.  It may be that some event may occur that might suddenly trigger the right key to be created, but even if this event does not take place, the brain keeps on trying one key after another.  Probably, while the brain is quiescent, it has less other tasks to undertake, and so can rush through more key trials, which is probably why one most often finds the memory one is looking for when one is actually resting, and apparently thinking of nothing.

I am not saying the above makes total sense, but it is the best sense I can think of at present to explain my observations of how the brain's memory works.

[dentstudent (OP)]

George – many thanks for spending the time unravelling the intricacies of your thought process. Perhaps we’re both learning something?

In principle, I agree with how your definitions relate to memory storage and retrieval. I have 1 area in which my thoughts are perhaps slightly different to yours, which can be highlighted in 2 areas in your text:

I do not believe you have any sensory memory of that incident, for if you do have a true visual recollection of the incident, it cannot be explained how you can remember that your mother and girlfriend were present, yet you do not recollect such components of the same visual image as anything pertaining to the clothing they were wearing.  Rather, you remember many facts of the incident, but the only way you are able to verbalise those facts is by trying to reconstruct a visual image by backfilling sensory information from the abstract facts that you recall

As to why it sometimes takes a long time to access some old memories; I suspect that after having searched its recent memories, and failed to find the information it is looking for, the brain then goes about trying to construct lots of different keys with which it might be able to locate the information in the longer term storage.  It may be that some event may occur that might suddenly trigger the right key to be created, but even if this event does not take place, the brain keeps on trying one key after another.  Probably, while the brain is quiescent, it has less other tasks to undertake, and so can rush through more key trials, which is probably why one most often finds the memory one is looking for when one is actually resting, and apparently thinking of nothing.

In the first paragraph, you discuss the premise that memory fills in the parts that it doesn’t remember with details from other events. In the second paragraph, you discuss the brain spending time finding keys to unlock memories that have remained closed for some time. My train of thought is this: My memory of the dog episode to date has been that I have recalled many times over the last 15 years the event and the pertinent information to the event, ie, those memories I shared yesterday. The recollection of clothing and so on are not relevant to the event in that the event title, if it were to be labelled for storage would be “Dog bite” and not “Things that people were wearing on such and such a date. Oh, and that dog thing too”. This means that I have not ever spent the time recalling or trying to recall what they were wearing. This is I think where we differ in thought. To me, this does not mean that I didn’t store this information somehow. All it means is that I haven’t accessed it for a considerable time, and hence the immediate links are missing. As you say, there may be elements that have been filled in through later or earlier events, in that I know about the collar, but that is not proof that I didn’t make a memory of it from that occasion. The second paragraph from your comments supports how I think it would be recalled, in that if I were given time, some other stimulus and perhaps trained in a different mechanism for extracting the memories, I would be able to. How much time, I don’t know. Perhaps even longer that our own lifetime?

So, as I say, in principle, I agree. Older memories are probably bits of an event which you then add knowledge to, to create a “pseudo” memory, but I do believe that it is all stored somewhere, and therefore that I do have a sensory memory of that incident - it’s just that the correct stimuli have not yet been applied, which is why it cannot yet be fully recalled.

[Karen W.]

Stuart do you remember that day when you got up.. had you already planed on the visit to the place you were bitten, or did that occur in your home? Perhaps thinking about the planing of that day and things you did before the event might trigger it, Did you shower that morning and did the dog bite your finger and draw blood did you get blood on your clothes. did it make a mess. did anyone help you remove the dig or did he just stop the attack or bite with your command.!4 years is a lot of time, things do get fussy with time and sometimes it helps to remember why or how your day started and why you were in the place you were when the bite happened.. that could help you recall things like clothing etc.. on you or the ladies at the time.

[another_someone]

In principle, I agree with how your definitions relate to memory storage and retrieval. I have 1 area in which my thoughts are perhaps slightly different to yours, which can be highlighted in 2 areas in your text:

As you say, the difference between us is not a huge gulf, and since both of us are speculating about things for which we have only limited hard evidence, some of it will have to come down to unprovable speculation on both of our parts.

In the first paragraph, you discuss the premise that memory fills in the parts that it doesn’t remember with details from other events. In the second paragraph, you discuss the brain spending time finding keys to unlock memories that have remained closed for some time. My train of thought is this: My memory of the dog episode to date has been that I have recalled many times over the last 15 years the event and the pertinent information to the event, ie, those memories I shared yesterday. The recollection of clothing and so on are not relevant to the event in that the event title, if it were to be labelled for storage would be “Dog bite” and not “Things that people were wearing on such and such a date. Oh, and that dog thing too”. This means that I have not ever spent the time recalling or trying to recall what they were wearing. This is I think where we differ in thought. To me, this does not mean that I didn’t store this information somehow. All it means is that I haven’t accessed it for a considerable time, and hence the immediate links are missing. As you say, there may be elements that have been filled in through later or earlier events, in that I know about the collar, but that is not proof that I didn’t make a memory of it from that occasion. The second paragraph from your comments supports how I think it would be recalled, in that if I were given time, some other stimulus and perhaps trained in a different mechanism for extracting the memories, I would be able to. How much time, I don’t know. Perhaps even longer that our own lifetime?

I don't think there is anything there that I disagree with, but I think what we have agreed about differs from the original premise that you ever stored an image of the event.

So, as I say, in principle, I agree. Older memories are probably bits of an event which you then add knowledge to, to create a “pseudo” memory, but I do believe that it is all stored somewhere, and therefore that I do have a sensory memory of that incident - it’s just that the correct stimuli have not yet been applied, which is why it cannot yet be fully recalled.

My early replay was phrased to deliberately indicate that you almost certainly did originally store more facts about the event than you now recall (how much more facts, and how much was missing right from the start will have to remain speculation).  But the key point I was trying to make was that right from the start, you never stored a complete unitary memory of the incident, but right at the beginning you had already broken the image down into separate abstract ideas.  This is why different ideas from the image have a different life span in your memory, for if they were only ever stored as a single unitary visual image, you would expect that you recall all of the visual parts from the image equally.  Even more so, if you remember the image, then you should readily remember what the people in the image were wearing, for those are visual parts of the image, even as you may forget that one of the people in the image was your girlfriend (for the fact that she was your girlfriend cannot be obvious from the visual image, but is an unequivocal abstract fact that was extracted from the original incident - it is part of your original interpretation of the incident, but not part of the image).

[dentstudent (OP)]

I think that we've taken this as far as we can - I also think that we've established that memory is a rather complex and intricate process. Thanks for the discussion George.

[coglanglab]

OK, I will try and explain my understanding about how memory works, but I will stress that this is my own conjecture based on my observations, and not anything authoritative.

Firstly, memory obviously comes in many forms.

another_someone's explanation was a nice start. There are definitely many, many types of memories, and they differ from each other in different ways.

For instance, if considering just visual memory, there is iconic memory, short-term memory and long-term memory. Visual iconic memory is almost like an echo or an after-image. It lasts only a very brief period of time (a few hundred milliseconds), and is essentially a reconstruction of the original visual experience.

Right after that, you have visual short-term memory, which is said to last a few seconds. Some recent research I did suggests that it isn't so much limited by time as by space. When you see something new, whatever was in your short-term memory gets pushed out in favor of the new information. You can also read these blog posts I wrote about visual short-term memory:

http://www.scienceblog.com/cms/visual-memory-does-it-even-exist-14213.htm [nofollow]
http://www.scienceblog.com/cms/whats-relationship-between-short-term-memory-and-long-term-memory-14135.html [nofollow]


Then, there is long-term memory, which we are all more familiar with.

And that's just visual memory, which is distinguishable for verbal memory, which definitely has long-term and short-term components. I don't recall if there is an iconic verbal memory as well.

Long-term visual and verbal memory, along with other types of memory, is generally considered to be part of declarative memory, which is generally your memory for facts. I believe declarative memory also includes "source memory," which is the memory for where you learned something. This is a bit different from the memory itself. It's one of the reasons advertising works. You remember that you heard Trident is the best toothpaste; you forget that you heard that in a commercial.

There is also procedural memory, which is the memory for how to do something, like ride a bicycle.

What amnesics have lost is long-term declarative memory. Procedural memory and short-term memory systems are all intact, which is why they can remember new facts only for short periods of time, but they can learn entire new skills (like how to play the piano) and it sitll sticks with them.

[another_someone]

http://www.scienceblog.com/cms/visual-memory-does-it-even-exist-14213.htm

Could not reach this link - had not problem getting to the other link.

[dkv]

There is no distinction ...
If we close our eyes and imagine a real world event then it illuminates the same area of brain which is used during "real" world event.
Dream theory can not be falsified.