Long-Term memory

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"I really didn't know an MRI would be able to determine anything about white matter.
I've heard many NLDers claim that it can't."
I could be mistaken about this...my reasoning was as follows. A structural MRI is, literally, like taking a picture of the brain. The white matter shows up as white, the gray matter as gray, etc. So if there's something strange about the white matter that would be visible to the naked eye, it ought to show up on a structural MRI. In practice, I don't know how many white matter abnormalities could actually be picked up that way. I would go with your NLD friends on this one.

"Why exactly are these studies normally so unwilling to give out MRI
results? What if the results yield some significant neurological issue?
Do they just send people on their way without telling them anything
about it?"
In most cases it probably isn't necessary--as you know, they take great pains to include the healthiest, most neurotypical people possible. I imagine if someone had a tumor or something, they'd be told. Consent forms do typically say that any information "that might affect your willingness to continue the study will be provided to you," and a tumor would seem to be a pretty extreme case of this.

It takes time to analyze fMRI results--first hours of preprocessing, then the basic contrasts, then whatever more advanced procedures you want to do. Basic fMRI data, AFAIK, aren't useful until preprocessing and basic contrasts have been done; the actual machine produces a 4D matrix of fairly meaningless numbers. In addition to actual analysis time, we spend a lot of time trying to interpret them--there's a lot of scratching our heads and referring back to prior studies to see if there's any precedent. People are under a lot of pressure to analyze the data and get it published as quickly as possible, so unless there's a very good reason, they're not going to analyze one person's data separately. I don't know what issues there are, if any, with structural MRI, although I would imagine it takes a lot of expertise to interpret the scans accurately.

Sedaka, I look forward to hearing more about the hippocampus, too.

Mosaicofminds wrote:

You probably aren't mistaken. One problem is that I don't know
exactly what type of MRI these NLDers had. None of the NVLDers i've
encountered online who said they had an MRI specified the kind
of MRI it was. They just said the MRI showed nothing in terms of
any white matter involvement. I don't know enough about white
matter abnormalities to be able to tell you which ones could be
picked up on structural MRI and which ones couldn't. I do know
that the NVLD syndrome is believed to be the result of SOME kind
of white matter involvement. It doesn't necessarily need to be an
actual absence of white matter. It could be a diffusion or some
other kind of abnormality/dysfunction of the white matter in various
parts of the brain. I'm pretty sure you know all this and you probably
know that the right-hemisphere contains a relatively greater amount
of white matter than the left. Thus the common NVLD deficits usually
involve abilities associated with the right hemisphere.

In any case....considering I don't even know what kind of MRI
these people had, I have no idea as to whether any white matter
abnormalities associated with NLD can show up on any type of
MRI or not. I've always heard that they can't and i've heard this
from professionals as well. Needless to say...agenesis of the
corpus callosum DOES show up on an MRI (at least structual
ones) and that CAN result in many NVLD characteristics in
people. As for any other type of white matter abnormalities
associated with the disorder, I just can't be sure what can and
cannot be determined by an MRI.





The necessary cases are the only ones I was wondering about.
I know that they need "healthy" neurotypical people for control
control groups. I'm sure that if anything serious shows up, the participate
would be told. In the case of the other poster's friend who participated
in this Pitt study, he was told nothing about his own MRI/s except that
there were "no gross abnormalities". I am guessing this person was
part of the "with autism" group, but many, if not most, people with
autism don't exhibit any "gross abnormalities" on MRIs.



While I wasn't aware of the actual details you shared here,
I was pretty sure this is more or less how it works. Obviously
it takes quite a bit of expertise just to interpret X-rays.
accurately. I was involved in car accident (with no loss of
consciousness or head injuries) when I was 17 and even
though I didn't have any injuries aside from some minor
cuts and scratches, the EMT advised me to go to the
hospital anyway for some spinal X-rays. I took her
advice and the technicians who read my X-ray results
told me I had a fracture in my C7 vertebrae. They put
me in a neck brace and gave me an appointment to
see a neurosurgeon. I had to wear the neck brace for
two weeks until my appointment. I took the X-ray film
to the neurosurgeon, he took one look at and told me
take the neck brace off and go home. There was nothing
wrong with my C7 vertebrae at all aside from a common
and harmless aberration. The neurosurgeon just said the
X-ray techs are incompetent and don't know what they're
looking at.

Keep in mind these X-rays were performed at a respected
major hospital in Pittsburgh, not some witch-doctor clinic
in the Columbian amazon. A somewhat opposite situation
occured to me after I was assaulted and robbed in downtown
Pittsburgh not long after the car accident. I was struck several
times in the jaw and I was in a great deal of pain. I went to
Allegheny general hospital for some X-rays of my head and
jaw. The results came back clean according to the X-rays techs
AND a doctor who also looked at them. They told me to go
home and that the pain would subside in a few days. The pain
didn't subside and I could even eat, so I knew something was
amiss. I went back for another set of X-rays at the same hospital
where my spinal X-rays were misread and this time they got it right.
I had a fractured jaw and even a doctor at Allegheny general hospital
failed to determine that from his own readings of the X-rays. Then it
was off to a maxilllofacial surgeon to have my jaw wired shut for six
weeks.


From what I know..... it's far easier to correctly interpret the results
of X-rays as opposed to those of an MRI. If the technicians (and even
doctors) can screw up on their interpretations of X-ray results, i'm sure
an accurate interpretation of structural MRI ones (maybe especially MRI's
of the brain) is formidable and time-consuming task indeed.

Last edited by Horus on 17 May 2010, 7:13 pm, edited 1 time in total.

Sedaka~


I watched the youtube video and I have several comments about
it. Considering all that was said about the reason for John's memory
impairments/hippocampal damage was that "his brain was damaged
as a baby", I can't be sure if this could be defined as an actual case of
developmental amnesia or not. DA is apparently quite rare and based
upon all i've read about it, it usually impacts episodic memory while
leaving semantic memory intact. There are supposedly a few cases of
DA in which semantic memory is also impaired and MAYBE in some
of these cases, episodic memory is left intact. Based on this video, it's
hard to determine if John's semantic memory is also impaired or not.
But there can be no doubt that his episodic memory certainly is.

There's pretty good evidence to suggest that there is not one
unified system governing declarative memory (semantic and
episodic.) and that selective damage to the hippocampus often
does not result in significant deficits in semantic memory.

In fact, the VK results mentioned in the following essay suggest that
essay suggest that the cortical areas surrounding the hippocampus
are largely responsible for the formation of context-free semantic
memory whereas the hippocampus is responsible for the storage
of episodic memory.




"Conclusion: In conclusion, recent evidence (VK) suggests that selective hippocampal damage affects episodic memory to a greater degree than semantic memory. To some extent this supports a view of episodic memory as embedded within semantics but it is not clear that semantic memory in developmental amnesics is near normal as some proponents of the theory claim. Although probably less damaged than would be expected by unitary declarative memory theory (Squire, 1987) it is premature to claim that such patients have normal semantic memory given that difficulties are likely to be cumulative and mediated by the complexity of their lives (which are unlikely to be normal given their episodic problems). Holdstock et al’s (2002) study would be especially interesting to replicate using developmental amnesic patients as this would provide a strong test of the complementary learning systems model outlined above. Any differences between acquired and developmental amnesic patients could then be more confidently attributed to developmental adaptation.



Squire’s (1987) notion of a unitary declarative system seems consigned to history by the development of functionally more interesting models based around aspects of this theory combined with a greater appreciation of the specific mechanisms through which the hippocampus could function as a learning device. Although there is dispute as to which areas of the brain exactly are damaged in different patients (c.f. Manns and Squire, 2003) an potentially more interesting issue and one brought up by the CLS approach of Holdstock et al (2002) is that of interaction with the complexity of the learning and testing environments. Extensions of this approach combined with functional scanning/ selective inactivation in healthy patients (perhaps during learning of more or less densely integrated semantic associates) look set to provide the most interesting next neuropsychological clues in understanding the organisation of our knowledge structures. It seems likely that if episodic memory is special to humans, that in the hippocampus, one at least of the systems that makes it special, also assists with complex structuring of semantic learning and disambiguation of similar stimuli".


http://members.tripod.com/cassius_cat/dev-am.htm




I suppose I should attempt to describe my own memory problems
problems in more detail. I need to make it very clear that I do not
believe my deficits in episodic memory are nearly as severe as the
ones experienced by John in this youtube video. The same would
be true of my semantic memory as it could be compared to an
individual like HM. My own problems in both areas seem to fall
somewhere within the *borderlands* between John/HM and normal.

They are not obvious to anyone save myself and again, they haven't
even come to clinical attention. I myself didn't even start suspecting
any problems with my memory until I started to play guitar at 15.
I was amazed by what other guitarists seem to be able to remember
in regards to solos/leads and songs with alot of complex and intricate
changes in them (chord changes or otherwise.) I seemed to have no
capacity at all to remember anything aside from a few very simple
and very short guitar solos/leads. Likewise....I wasn't able to play
songs with alot of changes whether these changes involved alot
of chord changes per se or changes in picking style, notes, bends,
pull-offs, hammer-ons, harmonics, etc....

As far as i've heard....music involves four distinct kinds of memory:

-Conceptual
-Auditory
-Kinesthetic
-Visual

I do have clinical confirmation of deficits in visual/non-verbal memory
and these are quite common for NLDers. Kinesthetic memory is probably
one and same as motor/procedural memory. I'm not sure how auditory
or conceptual memory are related to semantic, episodic and procedural
memory or if they're related at all. I suspect both auditory and conceptual
memory are functions largely, if not entirely, dependent on semantic memory
though.

Provided my ideas about the four aforementioned types of memory
are correct, there seems to be a "this far and no further aspect" to my
long-term memory in terms of semantic, episodic and procedural memory.
For example....i'm sure my semantic/episodic memory is much better than
HM's was in general. To try and illustrate this...i've been a voracious reader
all my life. I've probably read thousands of book's worth (within and without
the context of actual books themselves) of material in my life. All this reading
has allowed me to perform fairly well, probably better than most people, at
Jeopardy. In the clinical sense, it has allowed me to score exceptionally high
on the "Information" subtest on the WAIS IQ tests. That subtest is supposedly
a good indicator of one's long-term memory, but in my case, I think it's a very
misleading one.

For example...one the questions i've encountered on the Information
subtest was; "What is the name of the author who wrote Faust"? That
was a painfully simple question for me to answer as i've probably read
and heard that Goethe wrote Faust a thousand times. Therefore, alot of
correct answers to questions like this seems to allow psychologists to
assume the person they're testing has a good long-term memory. First
of all....considering that i've probably read far more than the average person,
I SHOULD be able to answer many of these questions correctly. It's hard to
view such questions as anything more than isolated and fundamental factoids
within a variety of subjects.

What's more telling to me, at least, is what I DON'T seem to be able
to remember in comparison to what most people are able to remember.
The ability to retain and recall a minute amount of very basic facts from
any given body of material alone is obviously not an indication of good
semantic memory and that's pretty much what the information subtest on
WAIS consists of.

But the real test of my long-term memory (at least in terms of semantic
memory) can be best illustrated by my experiences in college. Considering
I didn't even bother to study AT ALL in K-12 and still somehow managed
to pass (though by the "skin of my teeth" and it wasn't like I took any
difficult courses either. I was never in special ed, but I didn't take any
math courses beyond the pre-algebra level in K-12, nor did I take any
science courses beyond basic biology and physical science) through
all those years without repeating a grade and without having to attend
summer school. That said....my K-12 experiences are irrelevant here.

The introductory psychology course I took in college would be
a good example of how my semantic memory DOESN'T work.
To an extent....it would work in the context of the exams. The
retrieval/trigger "cues" of multiple choice, true/false and completion
on exams served me well and I got A's on all of them. I would read
(and highlight the relevant portions) a night or two before the exams
and then go in and ace the test. Now this may seem like an awful study
habit as opposed to "chunking" the material into memory over a series
of days, or even, weeks. In fact...maybe some may say this study habit of
mine is really the reason I claim to have long-term memory problems and
if i'd just gradually read and highlight the material over longer periods of
time, i'd come to see my long-term memory problems are merely products
of poor study habits.....not some neurological abnormality.


This is impossible for me to accept. I have read countless books outside
of the classroom environment, both non-fiction and fiction alike. I have
read these books over a series of weeks and sometimes even months. I
was usually very interested in all my recreational reading. I comprehended
most, if not all, of what I read and I often read the same books ten times or
more. Nonetheless....I only seem to be able to retain and recall a few basic
facts from anyone one of these books. When I say a few I can't give you an
exact percentage of what I can retain/recall, but let's just say it's far, far less
than what most people seem to be able to retain/recall if they read the
same books time and time again. Many would be able to retain/recall far
more than me after only one reading. So in this sense, my "study habits"
were not unlike the ones usually recommended and I STILL recall/retain next
to nothing of everything I read.

Futhermore....the efficacy of the retrieval/trigger cues is pretty
time-dependent. I found that everything was fresh on my memory
if I studied the night before an exam. If I stretched my studying out over
a series of days or weeks and then attempted to take an exam without a
thorough and complete review of the material, I probably would've failed
miserably.

So the efficacy of the retrieval/trigger cues is bound to degrade after
a series of time. Sure I could pass an exam with flying colors after
reading/highlighting the material the night before. Without a
comprehensive review, I probably wouldn't be able to pass the
exam a few weeks, or maybe even a few days, after my initial
reading/highlighting of the material.

Hopefully you can plainly see how all this doesn't bode well
for me within and without the academic milieu. Sure I could
pass many classes via the methods i've described. But god
forbid I should take a course which is largely dependent on
a recollection of the material I encountered in the prerequisite
course that I passed, perhaps even with "flying colors". For
example, suppose I could pass Anatomy and Physiology-I.
As far as I know...you will need to remember quite a bit from
A & P-I if you expect to pass A & P-II. This seems like something
I could never do, at the VERY least without constant and extensive
reviews

Outside the academic world....this is even more problematic.
Suppose I could get through law school with a constant and
comprehensive review of prequisite courses. What about when
it comes time to take the bar exam? I'm pretty darn sure you
have to remember much, though not everything of course, of
what you learned in law school in order to pass the bar exam.


Sure there are bar exam preps and reviews. But what happens
when I actually become a lawyer? What "reviews and preps" can
I rely on then when a client asks me some esoteric legal question
and I can't remember the answer? How about when I appear in
court in front of a judge? What "reviews" can I depend on then when
I can't remember basic legal procedures, terminologies, precedents,etc...
most first-year law students have down pat?


I'm sorry for this very long and rambling post, but try to understand
I find it very difficult to describe these memory problems of mine in
a manner others might understand. I often don't know where to begin
and just as often I don't know where to end. I just don't think others have
any point of reference since my problems seem to fall into a miscelleanous
category.


Basically what i'm trying to say is that it's really like I don't "KNOW"
much about anything. Can a pass a test in psychology using the
methods described in this post?...yes. Can I sit here and tell you,
strictly from memory, a whole lot of facts i've read about psychology
over the years? (many of which i've read time and time again)....no.

The same seems to hold true for my procedural memory. I can
remember how to ride a bike to this day even though I learned
as a child and haven't been on a bike for at least two years. I can
remember how to swim and it's something i'll likely never forget.
Same thing with driving a car and many other things which require
SOME minute degree of procedural memory. But if you ask me to
remember the insane amount of moves that go into an extensive
dance routine (even like the usual routines of Brittany Spears) I could
probably never do it no matter how much I practiced and rehearsed.

That's not to say i've ever tried....but it just doesn't seem like something
I could ever do no matter how hard I try.

Thus...it's almost impossible for me to talk or write about any subject
in the world based strictly upon what I remember about it. You might
get a few minute's worth of conversation out of me, or perhaps a page
or two of written material. But if I was expected to write a history of say,
the Third Reich, based upon what I REMEMBER from William Shirer's "The
Rise and Fall of the Third Reich" (a book i've read from cover-to-cover
more times than I can remember) you might only get a few pages out of
me and that's about it. Ditto if I was expect to give a talk about the
history, facts, characters, etc.....involved in the third reich. I should also
add that I am not able to THINK about anything any better than I could
talk about it or write about it. I decided to add this because alot of people
might be inclined to chalk this up as some difficultly with oral and/or
written communication people on the autistic spectrum encounter often
enough.

So in a very large nutshell..... this is how my memory doesn't seem to
work.

There is quite a bit more I could say about it.....and many more questions
I could ask. But all this would take at least twice as much typing as i've
already done and I doubt anyone will read what i've written so far.

As long as this post is...this is what I feel it takes to provide a
very rudimentary description of my memory deficits.

Sorry for all this and I certainly don't expect anyone to read it. Still...
I can hope someone might be willing to slug their way through it
and offer me any insights they may have. I personally am tapped
out of insights for the moment. Nothing seems to fit and I have yet
to have an "A-ha"! !! moment when it comes to my memory deficits.
This is part of the reason I often believe I don't really have any and
that i've somehow unintentionally exaggerated or even imagined the
whole thing.

I keep never being able to quite keep up with the pace of this thread... And I am reticent to post further w/o reading it to completion...

But w/o addressing the thread directly... if you like:

I have some links to websites in my signature that are basically search engines for scientific papers. I think you'd be able to find tons of stuff there... That's where I was (am) going to go hunting for you. A lot of them are free papers, but a lot aren't... But I have university access to most of these subscription papers.

If you happen to find any papers you'd fancy to read, you can PM me their citation and I could email them to you, assuming our uni. has that subscription.

Don't feel like you're putting me out... I need to be studying for my comps anyway, so I need to look all this stuff up. It's just been a long couple weeks in the lab.

Sedaka~

No worries at all....i'm barely able to keep up with it myself insofar
as responding to everyone's posts at least. I'm not even in school,
there's just alot of other things going on in my life.

I'll check up the websites you mentioned ASAP. It sounds like
a great source for the kind of info i'm looking for. If I find
anything among the subscription papers, i'll PM you the
citation.

Thank you very much for this, it means alot to me


Since I really don't have access to any professionals at the
moment who know anything about my issues, I sort have
to play my own neuropsychologist/neurologist.

And i'm hardly qualified for the job, but you and Mosaicofminds
have given some valuable info as well as some sources to
potentially valuable info.

Horus posted (in part): Very sorry for yet another immense post. As usual...i'm just seeking insight from anyone who might read this... As many of you know, I believe I have very unique and profound deficits in long-term memory. - Horus - Very few persons have perfect, long term memories. http://www.waiting.com/glossarym.html - (Memory) - http://www.waiting.com/glossarya.html - (Attention) - http://en.wikipedia.org/wiki/Neuroanatomy_of_memory - pgd

I have quite a bizarre memory.

I can recite the roll call/class register of my 7th grade class at school (nearly 40 years ago)

I can also remember the minutest parts of conversations that the other person is barely able to acknowledge.

Horus,

It could be that what you see as semantic memory impairment is caused by executive functioning problems. Attention is central to all aspects of memory and helps determine what gets transferred from short-term to long term memory.

Your dysthymia is also very likely to affect what gets transferred into your long-term memory. Anything that affects you motivation/attention also affects your short term memory and this will in turn affect your long-term memory. I know your neuron-psych eval said that you had good short-term memory. It is possible that you were very attentive during the testing because you are interested in finding out more about yourself (understandably so). However, during your everyday life your mood may affect your short term memory, which affects your ability to transfer new information to long-term memory.

Do you remember the facts/ideas/theories about memory and the brain that you put in these posts a few hours after you post them....or the next day? This would require semantic memory. I ask you this because you seem to very interested (maybe obsessively interested in your memory and therefore memory and the brain in general). Also, you have a very good vocabulary....vocabulary learning is dependent on long-term semantic memory!

There is some evidence that people with ASD's are impaired in procedural learning. Difficulty with the acquisition of motor skills and dyspraxia has been demonstrated in people with ASD. What makes you think that your procedural memory is impaired?

FYI, I've begun writing this reply while reading because it's too long for me to remember everything you mention, at least without reading it several times, and then thinking about it while I'm out walking ... so don't be surprised by its disjointedness. And I also didn't proofread ...

How odd. I am supposed to have quite a good long term memory and people often are astonished by the facts I present them about a topic - yet I have to rely on cues. If you asked me what I learnt in my entire biology classes in school, I'd stare at you and first say '... I ... don't remember?'
But my brain then starts to search and jump from link to link.
The thing is, I would probably be able to answer specific questions correctly, yet not be able to give an overview of what I learnt in biology - not immediately. Why should I be able to? It were ... more than five years, by any account, and I never before sat down and actually thought about it. The information is scattered all around my memory, is linked to items like cockroaches, genetic diseases, reproduction, metabolism ...
as that's where I actually use the information to comprehend things I might encounter in my daily life!
And if you gave me the task to do such a compilation of facts I know about a topic out of their normal trigger situation, I would use my episodic memory to start collecting the scattered information. I would both come up with a framework of the general time and to remember anecdotes that help me to find my way to more memories using episodic memory.

Now, if given the task to recall the arguments given in a book I read without the intention to later give a report about it ... ugh, difficult. I would not do such a good job, but I'd try to remember one argument or conclusion, and then try to find links in my mental system so that I can recover the other ones.
I'd basically try to cue myself.

As you say you can come up with the memories using external cues, I think your problem might partially lie withing the faulty episodic memory (which for most people serves as a cue giver), and faulty system of links between different memory items.
Maybe you can try to find relevant information for you searching brain connectivity theory? I think that might give you some leads.

You might also try to find something about ... recognition of familiar information. I can't find the right words for it atm, but your description of your study habits sounds like you're doing exactly what I often do: I look for whatever seems more familiar, and usually I am correct about it. (In a way I am very good at spotting familiar information, and interestingly enough that means that my brain shuts down. I usually can't even bear to read the same book twice, because I feel like I know everything standing it it already, and in a way I do ... just not in any way that's actually useful for me.)

Rote memorization is generally said to not help comprehension, because in order to comprehend a subject, you need to make mental connections to other items that belong to the same context, and therefor you can't utilize the learned subject in the way you can when you 'understood' it. And that makes it more likely to be forgotten with time. That is to say, rote memorization is an important part of learning, especially procedural learning.

I used to suffer from clinical depression for about ten years (plus anxiety and depressive moods before and after), which means it is most likely that my hippocampus was shrunk for a significant time span. I can't really tell whether the memories formed during that time are less than the ones from other times (I think so); and if, whether that was caused by the shrunk hippocampus itself, or by my horrible concentration and general lack of energy which caused me to make very few new experiences. However, during those times my episodic memory was a lot worse than it is now, so that for many things I learnt I can not put them in any meaningful framework other than the topic they belong to, and that usually works with triggers. (By the way you'd never have heared me say 'my long term memory sucks' or something as specific - while I was depressed, I would have complained about how stupid I am. Well, I did. Numerous times every day, though I tried to not let other people be around to hear it. The thing is that during my depression, I didn't have the processing capacity to actually pinpoint my problems!)

Your depression indicates that you are more likely to think bad things concerning yourself are true than that good things are. It's a self-defense mechanism that is backfiring. So, even though you might find your situation debilitating I think that your fears are exaggerating the impact this has on your capacity and holds you back from finding more possible coping mechanisms, just like mine do for me.

Do you have any sleep disorder that might inhibit memory consolidation?
I don't know if there is a way to test this yourself, but you're supposed to get better at a new task after one night's sleep. (I sometimes need two nights, don't ask me why.)

I also do a lot of memory consolidation and preparing it for usage in a verbal context while walking. Don't ask me why ... but often, when I learn very new things or new thoughts occur to me, for me it seems to be very clear and I feel like I can see and grasp it, yet when I try to explain it to others all that comes out is an incomprehensible mess. The same is true for any kind of procedural knowledge. I need to imagine telling people about it, and I need to do that while walking, before I actually can talk to people about a topic.

One thing I was reminded of while reading this was Vera Birkenbihl's 'Memory Optimizer' which partically works with re-structuring known information. I think the first demonstration they give was to say out loud the names of the months - in alphabetical order. (I listened to half of it and couldn't for the heck of it tell you the content other than this tidbit )

Wouldn't hippocampal damage mean that you actually not learn the new items, instead of learning them and not remembering where you put them until something leads you to it?

By the way, my visual-spatial memory and imagination are just fine, but I am really lacking in the department of auditory processing, imagination and memory. That's why I gave up playing the guitar ... I couldn't remember how the song was supposed to sound like, so I couldn't tell when I was wrong or right! But during the last years of my depression I spent a lot of time on learning English, and then picked up Japanese, then Spanish. I've been putting a lot of hours into learning to understand the spoken languages, and I actually got better at tasks like remembering spoken instructions in my native language! (Still far from where I'd like to be, though - I should be researching auditory memory like I did before I started reading in this thread, instead of babbling here.)


ETA: I just remembered something.
As I mentioned, I self-study languages (in a very messy way) and when you read through the relevant sites and boards, you'll soon find mention of so-called SRS, or spaced-repetition-software.
It's flash cards with repetitions set using the forgetting curve, and basically are there to test if you still know a specific piece of information. They are pretty good for vocabulary revision, but I know of people who use them for any kind of material they have to learn for school or college. (I am trying to get into that habit, too.)
Now, at one point I read a post by someone who referred by a paper from some university, in which was stated that it seems that the brain omits information it isn't tested on. But I simply can't find the paper! I found other ones about the usefulness of quizzes in long term retention, though.