[Added January 2005]
Normal sleep consists typically of periods lasting around 90 minutes that repeat 4 or 5 times each night.
Each period starts with a non-REM phase where we
go through 4 stages of sleep until we reach the stage of deep sleep with low
frequency electrical brain waves. Then the REM sleep starts with a lot of brain
activity and rapid eye movements. This ends when we get awake for usually a very short time and then a new cycle of sleep starts: light sleep, deep sleep, REM sleep.
Early experiments have shown that rem sleep doesn’t have any influence
on remembering lists of words or facts(i.e. declarative memory).
Instead rem sleep influences procedural memory (like the ability
to recognize patterns in a computer screen).Motor skills which depend
on procedural memory, are affected also by non-rem deep sleep.
Skills that require visual abilities are improved by both rem and
non-rem deep sleep.Sometimes also an hour with shut-eyes makes a big
It seems that different kinds of memory need different kinds
of sleep.This may explain why sleeping on a problem can produce sometimes
the result of getting awake the next morning with a solution.
Studies in animals have shown that during the sleep the same neurons
activated during the day by doing some task like traversing a maze, are activated again.
It seems as if during the night we are re-enacting (simulating) the same
experiences that we had during the day. This seems to produce two results:
- reinforce some pathways making permanent some memories
- drop memories connected to experiences considered irrelevant
This second task may be the result of the work done during slow waves deep
sleep when connections between neurons seem to be indiscriminately weakened.
So the sleep is perhaps a series of repeated cycles of pruning and strengthening neural connections that let you learn new skills without forgetting old ones.
[Added January 2005]
This fascinating article by Douglas Field on Making Memories Stick describes the mechanism how a short term memory becomes a long term memory at the level of the single neuron. For this to happen, a gene in the nucleus must be activated. This gene will produce “memory proteins” that are sent to all
neuron’s synapses but will strengthen only the particular synapse that has started the gene.
In this way a temporary activation of the synapse may become permanent.The same mechanism is also responsible , during recall, of memory reconsolidation. If protein synthesis is inhibited for some reason,
you can erase long term memories .
[Added January 2005]
In the film “Paris,Texas” by Wim Wenders, the main character is trying to get
his memories back walking around. When someone asks him how he knows where
to go, he answers : My body remembers for me. This sentence
has always made a great impression on me. It may mean many things. That when
we reach some place, we remember easily the way we got there. Another meaning
is that this knowledge is based on procedural memory so is unconscious
and difficult to erase. In Alzeimer’s disease the procedural memory is the
last to go.Amnesics including the famous patient HM (with hippocampus removal)
can still learn implicit knowledge of procedures.
It is possible to say from this that by including some procedural knowledge (especially if you are old) you
can improve your learning and memory? For example , with the use of the Web,
there is a big procedural component in our knowledge because we can learn
something by remembering how to get to that information. Another strategy
that I have found useful is the following: this is applied to learning a list
of let’s say 10 “concepts”. I give a number to each concept and write down
the 10 numbers on a sheet of paper in a ordered way:
1 2 3
4 5 6
7 8 9
As I write the numbers I try to recollect the “concepts” connected.
I will repeat the exercise many times each time starting with a new blank
sheet. The idea is to base the recollection of the 10 concepts on the
recollection of the procedure of writing down the ten numbers.
I have reinvented the method of loci!
[Added September 2004]
Since we dream so much, why the dreams we remember are so few? The answer is
astonishing:it is true that we dream a lot of time but most of this time
the brain circuitry needed to register those dreams is off. Only in the very
few moments that we get awake during the night, we are able to register
a few dream images , That’s all.It seems that every night, also if we think
that we slept all night, there are a few moments where ,for few seconds, we get
awake and can register the end of the last dream. This explains why,with some
training, everyone can remember many dreams every night.
[Added February 2004]
A small percentage of people with autism have some remarkable abilities: it is the
so called Savant Syndrome.They show mostly artistic abilities (play music or paint).The reason fo these abilities may be a normal right brain hemisphere that compensates for a damaged left hemisphere .
But what about the extraordinary memory that such people show(this phenomenon was depicted in the film Rain man)?The almost limitless memory of savant
people seems to be of the kind called procedural.This is the kind of implicit memory that we use when we learn to do something like riding a bicycle.
This memory is the last to be lost by people with Alzheimer.
Again, it seems that the damage that produces the autism has destroyed the explicit semantic memory, leaving intact this “low-level” memory.
Although the autistic people don’t know the meanings of what they learn,
they are able to remember a lot of things almost without effort. Some autistic savants
become able to describe how they do it. Their account is fascinating and may
be of great help in understanding how the brain works.
For example see the case of Daniel Tammet
and Temple Grandin.
[Added November 1997]
Memory reconsolidation is the process by which consolidated long term memories become temporarily labile after retrieval.
Apparently something happening during or shortly after the retrieval can
change and in some cases completely destroy the memory.
This has been shown experimentally with rats and other animals.
[Added October 2003]
I am a steady moviegoer and,as such, I like to speak with friends and relatives
about movies. In these talks it is of course important to remember
movie titles,actors and director names.
As the number of films seen increases , remembering all these names becomes more and more difficult.Of course this is understandable, you can’t remember thousands of names.
But what is really amazing is the following phenomenon: there are names that switch
on and off almost endlessly in your memory. You can remember them easily for a few
days , then they go away to come back after ,etc,etc. Also amazing is that some
names instead, you never forget.This is sometime understandable:for example, if you
have seen some actor or actress in person, you won’t forget the name so easily.
But perhaps this is not so difficult to understand.The problem is that we think about memories recall as a computer that retrieves information from storage.
If the information is there we must find it. Is it really like this?
Let’s think about it from the point of view of our mammal cousin: for example
a cat.There is no doubt that a cat has a memory. But what about recall: can a
cat like a computer recall anything anytime? No, he recalls something only if
there is some stimulus connected in some way with the object to be remembered.
This means that our ability to “remember at will” like a computer is
unique for us humans and has probably been acquired with language.
But as such it is not perfect and difficult to maintain.On the other
hand , “remembering like a cat” is more low level and is less damaged by aging.
[Added January 2003]
First a news:
Blog to Cope With Alzheimer’s Fog
Seniors in the early stages of Alzheimer’s disease, with mild to moderate memory loss, are writing Web logs to help them make sense of their daily lives. And the activity, they say, is slowing the onset of their symptoms.
Human memory is very difficult to study because of its complexity and the
impossibility to carry out experiments with living subject. But Alzheimer’s
disease is nothing else that a memory experiment carried out by nature.
A terrible experiment:what happens to memory if you destroy little by little
neurons almost everywhere in the brain in around ten years? Which memory
subsistem will go down first, which will last up to the end.
The result of this terrible experiment is that episodic memory will go
first. What lasts more is procedural memory.
In fact the memory impairment in Alzheimer’s patients is the same that
experiment aged people but instead of proceeding slowly it is very fast.
For this reason some scientist says that AD is not a proper disease but
only the simptoms of a very fast aging.
[Added April 2002]
With people that have no connection between the left and right brain hemisphere,
it is possible to do some startling experiment. You can show an object only
to the right hemisphere and see that the person is unable to name the object.
What does all this mean especially regarding memory? That we have in fact
two brains and each brain processes information in its way and has its
special way to store this information. So, an object , for the left hemisphere
is a word and for the right hemisphere is a shape. If they cannot comunicate,
the left hemisphere will be unable to give a name to some object that we know
very well. It is possible that also in normal persons, a reduced communication
between the hemispheres can be the origin of memory failings?
We know for certain, that in most people the left hemisphere is connected
to language and normally acts as the boss: i.e. if there are contrasts
between the two hemispheres, the left wins. This is understandable, otherwise
we will be all like Dr. Jeckyl and Mister Hide. But it is possible in some cases when,
we have problems with memory, to improve recall trying to use explicitily
the right hemisphere memory store? I am not an expert, so this experiment
that I have tried, has no scientific basis, but anyhow…
So, taking in account that my left hand is controlled by the right hemisphere
, when I have a problem recalling something, I will ask my left hand to describe it. What happens is that my left hand will make some sign in space
or against my body and I will try to use this sign to recall what I have
forgotten. Does it work? Yes, but I am not sure how it works.
Perhaps, it only works because it breaks some thought patterns that were
taking me nowhere. Perhaps some scientist should do some serious research in this field.
[Added March 2002]
This is a report on the effect of child abuse on their brain development: it gives some
glimpses on how the memory works in normal people. For example :
our memories have ,for survival purposes , all an emotional content. This
is regulated by the limbic system. For example, the amygdala (part of this system) is responsible to filter and interpret incoming sensory information in
emotional terms (it is a snake or a stick?) to help initiate the appropriate
response early enough(the “rational” processing of the same information comes too late for survival).
Persistent stress produces a smaller amygdala and this is connected to
depression, hostility and irritability.
Hippocampus (also part of limbic system) is important in determining
what information will be stored in long term memory: it seems that the
left part of this organ has smaller size as result of overexcitation of
the limbic system. This points to the possibility that there is a reduced
communication right-left hemisphere. In fact the organ responsible for this
communication, the corpus callosum, has a reduced size. The left hemisphere
is specialized in language whereas the right hemisphere is specialized in
spatial information and emotions.Is this reduced communication and increased
importance of right-hemisphere connected to the fact that disturbing memories
are stored in the right hemisphere? Can this be the cause of depression?