Memory

"Memory" is the title of the eleventh book in Lois McMaster Bujold's Vorkosigan series, and is best read after the preceding two books, Brothers in Arms and Mirror Dance.

In the beginning, Miles Vorkosigan goes into combat while still suffering from the after-effects of being killed and revived in the previous book. As a result, he suffers an epileptic seizure and injures friendly personnel. He tries to conceal this by falsifying his mission report, but he is caught lying by Simon Illyan, head of Imperial Security, and forced to resign from ImpSec.

Soon afterwards, Illyan's implanted memory chip which gives him a photographic memory begins malfunctioning, and Miles suspects that a plot to destroy Illyan's career and subvert ImpSec is in the making. His attempts to investigate this are blocked by Illyan's deputy, who appears to suspect him of the crime, so he asks Emperor Gregor Vorbarra to assign an Imperial Auditor to the case to give him the necessary authority. Gregor instead decides to give Miles himself a temporary Auditor's appointment; after Miles successfully resolves the crisis, this is made permanent.

One had a lovely face,
And two or three had charm,
But charm and face were in vain
Because the mountain grass
Cannot but keep the form
Where the mountain hare has lain.

- W.B. Yeats, 1919.

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From Cats by Andrew Lloyd Webber

This, the main Torch Song from the musical Cats, is the only number in the show that doesn't take its lyric from T.S. Eliot's Old Possum's Book of Practical Cats.

The lyric is, at least primarily, composed by Eliot, but it comes instead from Prufrock and Other Observations a 1917 collection aimed at an adult audience, where the OPBoPC targeted children. Given the erudition and obscurity of Eliot's adult poetry, it's not surprising that whereas the other songs in the show are simply the poem set to music, there are some significant changes - all simplifications- between this and its source poem Rhapsody on a Windy Night.

One must be fair, the changes are somewhat necessary:

TWELVE o'clock.
Along the reaches of the street
Held in a lunar synthesis,
Whispering lunar incantations
Dissolve the floors of memory
And all its clear relations
Its divisions and precisions,
Every street lamp that I pass
Beats like a fatalistic drum,
And through the spaces of the dark
Midnight shakes the memory
As a madman shakes a dead geranium.

I have been unable to find any attribution for who did the adaptation, unless it was Andrew Lloyd Webber himself - this seems unlikely, given the fact that he has never been known as a lyricist, though not impossible - I would personally be inclined to speculate they are the work of Don Black who was most closely associated with working with Lloyd Webber (collaborating with him on the show Song and Dance which was concurrent with Cats), although given his personal relationship with Elaine Paige, who was to play the lead and sing the song, it's possible that Tim Rice did the job.

Whoever penned the words, Memory became the best known, and most recorded track from the libretto, with the essential performance probably being that of Barbra Streisand, rather than either Paige or the other long-running female lead, Marti Webb.

memory (november 30, 2000)

my brain hit the re-Cord
  button one day,  i looked
 at him, forgetting his name
      and uttered,

  "  sam?  "   --  --

odd, since i've a picture of
    him a--or, i'd a picture
 of him at my kindergarten
birthday party --- ... but i
was at the time in, what, fourth
or third grade? . . .

      ~

   later i was influenced or made
   to  ..;,    .. well i decided
to challenge time by going in
   a--confuse time--circle and repeating
the same actions ... odd
thing to do at .. 10? 9?

   and so i circled the campus
feeling smart and there was mike
  and mister munzer  . . but
mostly joaquin wondering
    what the hell i was doing,
                             '
                           |/_

Memory that unfamiliar echo
Broad spectrum sliced into a rainbow
The here and now become a fading signal
The analog life begets the digital

And sometimes I think too much of the noise is lost
Since only the shattered pieces of the mirror are reflecting
And something about the wiring is a bit too lossy
Since I always remember the thought but never the thinking

So when you cross the same old street
You better make sure you move your feet
Because you might get hit crossing the way
And remember something that happened today

-Uberfetus, 1999

March chokes April
And I choke the throttle
The memory chokes Mary
And Mary chokes the bottle

Blue always wanted to die on a Saturday)
Yellow didn't find the car till mid-May)
Brown said the front half was buried in mud)
Red threw up because of all that blood)

I choke on the silence
And Mary chokes up
And Phil chokes on his vomit
While driving his truck

-Uberfetus, 2001

You wake up with the metallic penny taste of blood in your mouth again. This is one of those things you'll never get used to, like an orgasm. You lick your lips searching for any cut, but you find none. Maybe it isn't even your own blood. Your life was hard as a kid, your parents fought a lot, there were constant crises, so you blocked out all of your past. Every time you wake up to a question about anything, it reminds you of how blank most of your life is.

You wish you knew what this soft and ethereal stuff that memories are made of was, and why you could only hold on to some of it, or why some of it was buried deeper inside you than you could dig. There were prickly pinpoints of sentient thoughts that pierced into your consciousness, providing a quick look, but ultimately reminding you how unattainable you were to yourself. The cruel joke you're always playing on you.

You search your upper lip and mouth further for any source of the blood. Still nothing. Suddenly, the violent coughing starts. More blood taste. Congratulation Sherlock, you've figured it out. The blood is coming from inside. Then you notice the gash that runs along your gut and the fact that half your organs aren't in you any more.

It's funny how as the life drains from you, your mind has the inverse effect. Parts of your life that were gone forever come back. The flood of solace and consolation washes over you. The beauty of your personal mystery, however, begins to slowly fade into a hard reality. Now you remember why you blocked out your life. The ugliness replaces the justification you feel in knowing yourself again.

Maybe death is just a final discovery of yourself and everything that's in you. A total realization of your entire life in a second. They say that your life flashes before your eyes before you die, but what if your life is a reel of hate and sadness? There is no heaven or hell; there is only a moment of reflection on everything stored in your brain.

You taste the blood again, and you're starting to get light-headed. You are now little more than a husk of a person experiencing your whole life over again, and soon you will be less than that. Just before you lose all consciousness, right before you submit, you remember the one time you were happy and content in your life, a time when the anger and hurt was gone, and you die more complete than you ever lived.

As virtuous men pass mildly away,
And whisper to their souls to go,
Whilst some of their sad friends do say,
The breath goes now, and some say, No;¹

Memory is the mental process of storing and retrieving information in the brain. There are various levels of memory processing and different types of storing capacities that accompany each level. When information is received in the brain, it goes through several levels of sensory processing while it is stored; this is how human beings learn, by storing previously experienced environmental signals and comparing new ones to the ones already stored in the brain. The basic information-processing model for memory functioning is as follows:

Sensory Input → Sensory Memory → Short Term Memory → Long Term Memory

As information progresses through each of these levels, there tends to be a greater chance for retention farther into the future.

Levels of Memory

• Sensory Memory: Sensory memory is defined as the capacity to remember minute aspects and physical features of an object for very brief periods — most likely about a second or less. Due to this, sensory memory is almost indistinguishable from perception itself. This type of memory remains largely in theory; few analyses have been performed on information while it is in this stage of processing. The human mind cannot be directly aware of information while it exists in this level in the brain since it is so fleeting. It tends to be understood as the recognition of a perceptual whole, such as the brief memory of the experience of a faint sound or a briefly viewed image.

• Iconic Memory: Sensory memory is broken down further to include visual sensory memory, which holds a visual stimulus for the span of about one second. One of the best examples of how iconic memory functions is to imagine how your brain responds when viewing a lightning bolt. The image flashes for only a brief moment, yet the form of the lightning will linger in iconic memory for a second or so after the stimulus is removed.

• Echoic Memory: Another type of sensory memory is echoic memory, which accounts for sounds that have just been perceived. One of the easiest ways that this type of memory can be recognized is in the interpretation and processing of speech. As a word is pronounced by someone, we perceive it one syllable at a time. In order to grasp the whole word, each sound must be temporarily stored in the brain in order to more fully understand them later. If it weren't for this type of memory, then speech would be a disorganized chaos; humans would be unable to integrate information as it was delivered to them via speech.

• Short Term Memory: Short term memory is very similar to sensory memory in that its capacity is very limited by both the amount of information that can be held in it and also the duration that information can be held. In order to illustrate the capacity of short term memory, try the following.
  
  Read the numbers below only once and then close your eyes and repeat them to yourself:

3 8 1 4 7 0 2

More than likely, you had little difficulty recalling those pieces of information. Now, try reading the following different set of numbers once and closing your eyes to repeat them again:

1 6 2 9 0 4 3 7 2 5 1

Most people with normal memory capacities cannot recall 11 pieces of information in succession after having read them only once. This is because these stimuli were stored in short term memory, which has a capacity of between 7 and 9 pieces of information for the average person.

• Phonological short term memory: This is a type of short term memory that relies strongly on long term memory. Often when we are observing our surroundings, we will recognize certain objects, such as a tree, and we will think the word "tree." "Thinking" this word in this way is called a subvocal articulation, which is defined as an unspoken speech utterance. This is a manner of retaining information about our surroundings that integrate our language capacities with our perceptive faculties.

Subvocal articulations can also be used when information is transferred from short term memory to long term memory. This process is called the articulatory loop, and is part of the newer theories of working memory, an expansion of short term memory. Basically, this occurs when a person attempts to remember a piece of information by repeating it to themselves as well as recalling a mental picture of that piece of information to enforce it both verbally and visually.

• Long Term Memory: Long term memory holds information that is stored on a semi-permanent basis. There are no known limits on this type of memory. It occurs due to connections that are formed between neurons in the brain that are fairly static. Researchers argue that there can be strong connections between short term and long term memory. For example, the set of English characters "TXLKB" is much more easily recalled than the set of Greek characters "ΓΙΑΔΞ" (assuming that you're more knowledgeable of English than Greek, and have average memory capacities). This is because English letters have been learned by English-speaking people, and are stored in memory much more easily. This is related closely to phonological short term memory.

• Episodic Memory: This is a type of long term memory that acts as a recorder for events and experiences.

• Semantic Memory: Semantic memory is another type of long term memory that is associated with memories of data, such as vocabulary and general knowledge.

• Kinesthetic Memory: When performing physical tasks such as writing and walking, a type of memory known as kinesthetic memory is used. This type of memory is still highly theoretical; it is difficult to apply limits to it due to the lack of clinical testing. It applies to sequences of movements of the muscles and their relationship to each other while in motion, which is all retained in these types of memories.²

The articulatory loop is one process of encoding information into the long term memory. Further, there are two groups of long term memory processing.

• Effortful Processing: As its name suggests, this type of memory processing refers to the ways in which we consciously try to remember something. When students use flash cards to stimulate their minds visually and verbally, this is one example of effortful long term memory processing.

• Automatic Processing: This type of long term memory occurs when information is recalled with little attention to them. This can include events that are traumatic or startling.

Memory Conditions

• Conduction Aphasia: This condition results in the inability to remember words that are heard, even though the person might be able to respond to them at the time. This condition is caused by damage to Wernicke's area and Broca's area in the brain.

• Retrograde Amnesia: This condition involves the loss of previous long term memories, especially those concerning the individual's life. Often times, this is caused by a severe blow to the head. Usually this will result only in the loss of recent long term memories, rather than information that the person has known their whole lives. The reasons for this are still being researched.

• Anterograde Amnesia: This condition results in a patient being unable to form new long term memories after the time of the brain damage. Usually, they will be able to remember information for a period of several minutes, but beyond that they are unable to retain anything (this is Leonard's condition in the film Memento, which is a good example of what this disorder is like). They are often able to discuss things that happened to them before their injury, but they will not even be able to remember people they've see daily since their brain damage.

• Eidetic Memory or Photographic Memory: True to its name, individuals with photographic memories are able to recall events, objects, or information with extreme visual clarity. Some people experience similar types of memories when they have what is known as a flashbulb memory, an extremely lucid recollection of an event. However, individuals with photographic memories experience this all of the time. The transition between short term and long term memory is sometimes nonexistant for them, as they can often remember whatever they like without practicing the articulatory loop that many others do. Reasons for the existence of photographic memories are unknown. However, they are often tied to other conditions such as synesthesia, and I believe that it could be linked to a much more developed hippocampus; this is the area in the brain which controls memory.

¹John Donne. A Valediction: Forbidden Mourning.
²Information on kinesthetic memory from http://www.handle.org/miscinfo/glossary.html. Thanks to dutchess for reminding me of this type!

Sources:

E. F. Loftus. Memory. © 1980; K. Haberlandt. Cognitive Psychology. © 1994; N. E. Spear. Memory: Phenomena and Principles. © 1994. — Node your library.
This is a node in progress. I'm thinking of adding a section regarding learning & long term memory, but I need to gather more of my notes together. Suggestions or additions for this? I'd love to hear them.

Philosophers have been thinking about memory for thousands of years. Plato in the 4th century BC suggested the Wax Tablet Hypothesis. This theory assumes that the mind accepts impressions as if it were a wax tablet drawn on with a sharp object. Once the impression is made it remains but it wears away over time leaving a smooth surface and hence no memory. Therefore, memory and forgetting are just opposite aspects of the same process. This explanation was accepted with only minor variations until relatively recently but it is now generally accepted that they are two different processes.

Aristotle had a theory about the physical location of memory. He realised that part of the hearts function was to move blood around and thought that memory was based on the movement of blood. Therefore forgetting could be attributed to a gradual slowdown of these movements.

The physician Galen in the 2nd century AD did a great deal of work with the various biological processes of the body and concluded that memory resided in the brain, not the heart. The question then becomes where and how does the brain encode memory?

It is now generally agreed that memory is located in the cerebrum, a large portion of the brain covering the surface of the cortex. But exact localisation is still difficult.

David Bohm (1917-1992), a physicist by profession, was one of a number of scientists that suggested the brain can work in a similar way to a hologram in one very important aspect. If a holographic photographic plate, which is simply a piece of glass, is smashed into pieces, each piece can still be used to show the entire hologram, albeit slightly blurred. Just as each part of a holographic plate contains a minirecord of the overall picture, so too every part of the brain may include all memories.

As the brain has no nerves to carry pain impulses, it is possible to open up the top of the skull, hopefully under local anaesthetic, stimulate various parts of the brain and ask the patient about it. Dr Wilder Penfield did some experiments in the 1930s and found that stimulating various areas of the cortex elicited a range of responses but stimulating the temporal node could bring back memories in all their glory, including even the emotional content. Some of these memories, such as childhood memories, couldn't be recalled in the normal way. It was Penfield's belief that the brain records everything - or at least everything we pay conscious attention to - and the main reason we forget is therefore a breakdown in the recall mechanism.

As a side note, there is evidence to support the idea of that some forms of memory are not necessarily stored in the brain but can be encoded in RNA (which is produced by our DNA). In one experiment for example, when the RNA from one rat was taken and injected into another, the second rat remembered things the first rat had been taught. While this is not conclusive evidence for the concept of genetic memory (as the RNA was not a copy produced by DNA passed on to the next generation) it is an interesting idea.

Why do we forget?

With these modern theories of how memory works, the main idea is that once memories are stored they are there for the rest of our lives (or even longer in the case of memories carried in RNA) and forgetting is equated with simply being unable to recall the correct memory.

Remembering can be broken down into 3 parts:

1. Recording
2. Retaining
3. Retrieval

This can be illustrated by comparing memory to a filing cabinet. First you put the information on a piece of paper (Recording). Then put it in the file cabinet under the appropriate heading (Retaining). Later, if you want it, you go back and get it out of the filing cabinet (Retrieval). Looking at this, it can be seen that to help us remember it would be good to have an efficient filing system. This corresponds to memory aids.

But there are also other problems that may contribute to poor memory that come into play at the one or more of the three stages of remembering. Some of the major ones are:

• Emotional Blocks - A mental barrier that we use to protect ourselves from things that we perceive could cause us harm, error, or ridicule. Obviously there are many valid reasons for such blocks and various kinds of therapy if you have a serious emotional block. One example of a less serious emotional memory block is a person who as a child didn't have any playmates and his closest friend was probably the housekeeper. However, as he moved around a lot such friends came and went. Now, as a lecturer he can remember the names of most of his students except for the ones he cares about the most. This is possibly because in his childhood he found that missing people was less painful if you didn't know their names and it is in anticipation of his students leaving that he didn't remember their names. In such cases, once the emotional block is realised it can be discarded, or strategies made to work around it. But it is important not to discard a block until you are sure you can live without it; after all, it is there for a reason.
• Diet - With a 'well balanced' diet you will be able to remember more than if you had sub-standard diet. Unfortunately, brain chemistry is so complicated that it is hard to say what a well balanced diet actually is.
• Illness and injury, - The most obvious illnesses and injuries that affect memory are various head injuries, amnesia, Alzheimer's disease.
• Allergies - Generally allergies only play a very small part in memory problems but anything that disrupts our physical or emotional balance can make us forgetful.
• Drugs - Specifically recreational drugs but any drug that affects mood, perception or alertness will also affect how you process information.
• Alcohol - See above. In extreme circumstances people can experience state dependency where things learned sober are hard to recall when drunk and vice versa.
• Smoking - Tests have been carried out that showed non smokers could recall better than smokers. It has been suggested that this is because smoking may impair the amount of blood supplying oxygen getting to the brain and the lower oxygen levels result in decreased memory efficiency.
• Lack of exercise - While this does not necessarily impair memory function it does slow down response time and good general health and physical fitness is a powerful aid to memory.
• Fatigue - Occasionally fatigue can be an aid to remembering as we float in free association mode but it can also inhibit the actual creation of new memories.
• Tension - This can be a vicious cycle. You are in a situation and don't remember an important detail. The more you try to remember it, the more tense you become and less able you are to remember. Tension can have the opposite effect of fatigue; while you cannot remember previously known information there is evidence that adrenaline and other hormones produced when you are excited or under stress help lock new memories in, possibly simply as a byproduct of making your senses more acute.

Old age is not a reason for memory loss. It can be seen that there are a lot of factors that can contribute to memory loss of a greater than normal degree. With the elderly memory loss can come as a side effect of being unable to adequately look after themselves, such as substandard exercise and diet, or as a result of illness, injury, or medications.

Update: Thanks to dscotese who pointed out that studies have shown that adrenaline improves memory up to a point, and then rapidly and severely degades it, one explanation of traumatic blockage.

Buzan, Tony "Use your Memory" Revised Edition, 1989

Higbee, Kenneth "Your Memory: How it Works and How to Improve It", 1990

Minninger, Joan PhD. "Total Recall: Successfully Boost your Memory Power", 1984

Memory can be divided into two main categories. There are memories as we usually understand them, that is episodic memories, and generally memories which have some sort of abstract or overt meaning to them (such as remembering what we had for breakfast, and how we felt after we ate it). But there is another type of memory function that we are not really aware of - learning responses based on environmental stimuli. Learning is in fact, a memory function.

The second type of memory function is known generally as stimulus-response learning. In stimulus-response learning, the more a given sensory stimulus is associated with a particular beneficial behaviour, the connections between the sensory input of the stimulus and the behavioural functions are strengthened. The structures involved in this type of memory are therefore the connections between sensory neurons and motor functions. This sort of learning has been demonstrated experimentally very many times. An example is monitoring the responses of rabbits to a puff of air directed at their eye. When the somatic sensors around the eye detect the blast of air, it elicits a reflex response of blinking. However, if the blast of air is preceded by an auditory input of a certain tone sounding, then the rabbit learns the association that a blast of air is to follow, and blinks in anticipation of that blast of air. This is shown by monitoring the onset of blinking with respect to the onset of the tone and the onset of the air blast. Without the tone, the rabbits blink after the air blast. With the tone, the rabbits blink before.

This process, often called classical conditioning, is not altogether cognitive - i.e., the rabbits do not hear the tone and necessarily "decide" to blink - it becomes an automatic response. This is down to the restructuring of neurons in the rabbit's brain. In the brain, there are very many thousands of connections between neurons from many areas of the brain. The strengthening of these connections is the basis of learning and memory. To describe, I will focus on a basic description involving the rabbit blinking mentioned above. As I said, such a response relies on the strengthening of connections between sensory neurons and motor neurons. This process is described by the Hebb rule. The Hebb rule states that if a synapse repeatedly becomes active at about the same time the postsynaptic neuron fires, changes occur in the structure or chemistry of the synapse that serves to strengthen it. To simplify, let us assume that just one neuron detects the tone, one neuron detects the air blast, and one neuron controls blinking. The normal situation, without the tone, involves the neuron which detects the air blast firing, thus triggering the motor neuron controlling blinking. But with the tone present, the neuron detecting the tone fires as well, at around the same time the neuron detecting the air blast does. The synapse between the terminal button of the auditory neuron and the motor neuron strengthen to such a degree that the firing of the auditory neuron alone can cause the postsynaptic motor neuron to fire. The result is blinking as a response to the tone rather than the just the air blast. It is this basic system that allows for an enormous amount to be learnt as a response to environmental stimuli.

Investigators have found the mechanism that allows synapses to be strengthened. It is based on NMDA receptors located on the postsynaptic membrane. An increase of calcium in the postsynaptic membrane causes the strengthening of the synapse. NMDA receptors allow the influx of calcium only under certain conditions. The flow of calcium is usually blocked by a magnesium ion, but this ion is ejected when the postsynaptic membrane is depolarised. However, there needs to be another condition before calcium can flow and that is the activation of the presynaptic terminal button. This activation of the presynaptic terminal button causes it to release glutamate, a substance which the NMDA receptors are sensitive to. Only when these two conditions are satisfied can calcium enter the postsynaptic membrane. This calcium then activates calcium-dependant enzymes (such as PKC and CaM-KII), which in turn bring about greater release of glutamate from the postsynaptic terminal button. This is the mechanism that allows the strengthening of synapses so that learning can occur. This process is known as causing an increase in long-term potentiation, since it increases the magnitude of the EPSPs (excitatory postsynaptic potentials) in the postsynaptic cells over a long-term.

This process of learning can also be applied to operant conditioning. Operant conditioning (or instrumental conditioning) is more concerned with behavioural responses, which are more complex in nature than the simple reflex actions, such as the rabbits' blinking, which are involved in stimulus response learning. If behaviour in response to certain stimuli is beneficial, then that behaviour tends to be repeated. This is how animals learn from experience. This process is called reinforcement, and it has been found that it is associated with the release of certain neurotransmitters, dopamine being a particularly important one. These neurotransmitters can induce the synaptic plasticity mentioned above, by facilitating long-term potentiation. B. F. Skinner showed that animals could be made to repeatedly perform a certain task, such as pressing a lever, if that task was rewarded with a piece of food. The beneficial nature of a task corresponds to the release of dopamine agonists in certain areas of the brain, prominently the nucleus accumbens. To corroborate the reinforcing nature of dopamine, it has been demonstrated that laboratory animals, and humans, will repeatedly self-administer dopamine agonists, like amphetamine or cocaine. Further evidence for the importance of dopamine in operant conditioning is that injections of dopamine antagonists in laboratory animals results in no ability to learn from behaviour - presumably, it blocks the reinforcing effects of stimuli. Several areas have been identified as being locations of synaptic change in operant conditioning - the nucleus accumbens, the basal ganglia, the frontal cortex, and some suspect the prefrontal cortex is involved too.

Perceptual learning is an area that is much more greatly associated with memories. By this I mean those memories which are based on sensory information and we can "recall", like "what did I have for breakfast". Very simple perceptual learning can be done subcortically (such as the processes involved in the types of learning above), but for memories proper, we need to use many different areas in association with each other. Perceptual input causes changes in the neural circuitryof the appropriate sensory association cortex in accordance with the principles of Hebb law. These changes are the basis of memories. This has been inferred experimentally, for example by Mishkin (1982), by showing that lesions in the inferior temporal cortex (where the visual association cortex is located) disrupts an animal's ability to remember what it has just seen. Such a lesion might mean that monkeys fail a task where it is presented with an image which is subsequently removed, then two images are presented for it to choose from, where touching the image that corresponds to the one it has just seen results in a reward.

In order for these changes in neurons and synapses to mean anything, there needs to be a system to combine them in a meaningful context. An example of such a system is the central nucleus of the amygdala. Here, associations between emotions and sensory stimuli happen. For instance, if in an experiment a rat is given a small electric shock via the floor of its cage just after a tone sounds, then the associations between the auditory inputs, somatosensory inputs, and the emotion of fear in relation to the tone, are made in the amygdala, thus producing a more complete memory than just a reflex action.

However, the main area of the brain involved in the recalling of memories is the hippocampus. Its function is to put events into context so that the correct information can be retrieved from other areas of the brain, thus recalling a memory. To do this it has many inputs from the sensory association cortices, the motor association cortex of the frontal lobe, the amygdala (which provides information on odours and dangerous stimuli as well as associating sensation with emotion), and also the neural circuits involved in classical conditioning. These inputs provide all the information needed to construct a complete memory given some kind of prompt for that memory (a question someone asks perhaps). The hippocampus can "know" an animal's location in space through neurons that respond according to the relations among objects in the animal's environment. It can therefore keep track of an animal's location in space. This is the function that it is believed the hippocampus had originally, but evolution has enabled it to now do more. It has been shown that damage to the hippocampal formation does disrupt the ability to learn spatial relations. For instance, rats will not remember which arms of a radial arm maze they have already visited to look for food (however, they can learn which arms never contain food). Such rats also cannot learn the location of the hidden platform in Morris' milk maze. Hippocampal damage disrupts ability to distinguish events in terms of time as well as space. This strengthens the idea of the hippocampus as providing a contextual basis for parts of memories to be associated together, as time and space are the qualities required for such a context. Research has shown that hippocampal damage disrupts the ability to distinguish context. For instance, going back to the blinking rabbits, Penick and Solomon (1991) found that rabbits with hippocampal damage would perform the whole air blasting task exactly the same when in a different location, whereas normal rabbits showed a change, in that they would lose some of the strength of the conditioned response. Apparently, the damaged rabbits could not remember the context in which the learning had taken place.

In humans, damage to the hippocampal system results in anterograde amnesia (the inability to remember any events after damage occurs, and also those events that had taken place a number of years before damage). Apparently, they are unable to reactivate the pattern of activity in the hippocampus which retrieves the memory. Such patients can still perform short-term memory functions, such as those needed to carry on a conversation, and ordinary stimulus-response learning appear unimpaired. For instance, HM, a very much studied anterograde amnesia sufferer, was found by Milner and Corkin to improve in mirror drawing tasks. Each time he attempted them he improved, even after a long spell between attempts. He had no memory of ever doing such a task before (he chalked his skill down to natural talent!), but clearly he had improved his motor skills in some way. What is clear is that anterograde amnesiacs have problems in relational learning, rather than such types of learning as stimulus-response learning. Thus, the hippocampus cannot be the only area involved in memory, though it is an important one. In fact, anterograde amnesia can be caused by damage to both medial temporal lobes, or a thiamine deficiency due to chronic alcoholism.

In fact, there must be other areas at work. Anterograde amnesiacs after all can still remember things some years prior to damage to the hippocampus. So if the hippocampus was the only structure used in the retrieval of memories, then such patients would remember nothing at all. What this other structure or mechanism is that allows retrieval of these very old memories, is still an unanswered question.

So, the hippocampus can be thought of as the centre of memory retrieval. But it requires inputs from very many areas of the brain, and in turn, these input areas themselves have many inputs. So from this perspective, the whole brain has some part to play in memory. For instance, it has been found that people who suffer damage in area V4 of the extrastirate cortex can not only no longer perceive colours, but they cannot remember what colours were like at all. However, simple perceptual learning, like stimulus-response learning, appears to be somewhat distinct from more complex memories, since hippocampal damage does not impair these functions. But these functions still go on in many areas of the brain - after all, we have to learn many things in many areas. The memory system is therefore very large and very complex, and as a result, may never be fully understood. Even those parts of memory function we do understand are still amazing and it is astounding that they can have such a sophisticated result as the recollection of events long since past.

In the world of knitting, the word "memory" can refer to two things (besides, that is, the obvious).

First, circular knitting needles are often described as having a certain amount of memory. In this case, having memory is a bad thing.

Circular knitting needles, or "circulars," are two shortish knitting needles that are joined by a cord. They are most often used for knitting in the round, which is to say making tubes for the bodies of sweaters and the like.

Cheap circulars have lousy plastic cords that can be hard to coax out of the position they came in the package. Needless to say, a tight coil is not very useful for knitting. The more stubborn cords will continue to try to twist into tight loops even though you'd rather they curved gently.

The problem can be mitigated by soaking the needles in hot water and "teaching" the cord to straighten out. However, as soon as you are finished your project and store the needles, the cord will coil into a useless shape again and will probably need to be re-heated the next time you use them.

Good quality circulars have flexible cords that go exactly where you tell them to. If cheap circulars resemble a stubborn piece of wire, good circulars resemble the chain of a necklace. Unburdened by memory, a chain changes shape whenever you move it. Similarly, good circulars hold the weight of your project without fighting you.

The second, more common reference for the word "memory" has to do with types of fibre. In this case, having memory is often, though not always, a good thing.

Wool and other animal fibres are said to have a lot of memory; cotton and most plant fibres (along with synthetic fibres like acrylic) are said to have little. What this means is that if a woollen garment is moistened with warm water and pinned into shape -- a process called blocking -- the garment will "remember" that new shape even after it dries. Thus, a knitter who wants to straighten the edges of a scarf or align the shoulders of a sweater can block it into the shape she wants, fixing minor sizing mistakes as she goes.

If you pin and moisten cotton, it will obey you for a while, but it will tend to return to its original knitted shape as soon as it's dried and removed from the table. This is what it means to say that cotton has no memory. Blocking cotton garments is not completely useless, but it can't be depended upon to resize or reshape something that was not knit perfectly to begin with.

Low memory is sometimes desirable in a knitted item. For instance, cotton dishcloths are much more useful than woollen ones, since they keep their shape even after contact with water. But in the case of clothing, high memory is usually preferred, so that the object can be shaped by blocking.

Mem"o*ry (?), n.; pl. Memories (#). [OE. memorie, OF. memoire, memorie, F. m'emoire, L. memoria, fr. memor mindful; cf. mora delay. Cf. Demur, Martyr, Memoir, Remember.]

1.

The faculty of the mind by which it retains the knowledge of previous thoughts, impressions, or events.

Memory is the purveyor of reason. Rambler.

2.

The reach and positiveness with which a person can remember; the strength and trustworthiness of one's power to reach and represent or to recall the past; as, his memory was never wrong.

3.

The actual and distinct retention and recognition of past ideas in the mind; remembrance; as, in memory of youth; memories of foreign lands.

4.

The time within which past events can be or are remembered; as, within the memory of man.

And what, before thy memory, was done From the begining. Milton.

5.

Something, or an aggregate of things, remembered; hence, character, conduct, etc., as preserved in remembrance, history, or tradition; posthumous fame; as, the war became only a memory.

The memory of the just is blessed. Prov. x. 7.

That ever-living man of memory, Henry the Fifth. Shak.

The Nonconformists . . . have, as a body, always venerated her [Elizabeth's] memory. Macaulay.

6.

A memorial.

These weeds are memories of those worser hours. Shak.

Syn. -- Memory, Remembrance, Recollection, Reminiscence. Memory is the generic term, denoting the power by which we reproduce past impressions. Remembrance is an exercise of that power when things occur spontaneously to our thoughts. In recollection we make a distinct effort to collect again, or call back, what we know has been formerly in the mind. Reminiscence is intermediate between remembrance and recollection, being a conscious process of recalling past occurrences, but without that full and varied reference to particular things which characterizes recollection. "When an idea again recurs without the operation of the like object on the external sensory, it is remembrance; if it be sought after by the mind, and with pain and endeavor found, and brought again into view, it is recollection."

Locke.

To draw to memory, to put on record; to record. [Obs.]

Chaucer. Gower.

© Webster 1913.