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Friday, December 17, 2010

My Brain With bvFTD - All About Memory



A Technical Look At Short-Term Memory

Since one of my main difficulties is with Working Memory I wanted to know more about it. There has been a large amount of research on memory since I took my last Psychology class. About all I can remember of brain anatomy is... Brain Stem! Brain Stem!

The following is copied directly with permission from the web site, The Brain From Top To Bottom. It is a great site, so expect to see more in the future.


SHORT-TERM MEMORY




In the course of a day, there are many times when you need to keep some piece of information in your head for just a few seconds. Maybe it is a number that you are “carrying over” to do a subtraction, or a persuasive argument that you are going to make as soon as the other person finishes talking. Either way, you are using your short-term memory.

In fact, those are two very good examples of why you usually hold information in your short-term memory: to accomplish something that you have planned to do. Perhaps the most extreme example of short-term memory is a chess master who can explore several possible solutions mentally before choosing the one that will lead to checkmate.

This ability to hold on to a piece of information temporarily in order to complete a task is specifically human. It causes certain regions of the brain to become very active, in particular the pre-frontal lobe.


 This region, at the very front of the brain, is highly developed in humans. It is the reason that we have such high, upright foreheads, compared with the receding foreheads of our cousins the apes. Hence it is no surprise that the part of the brain that seems most active during one of the most human of activities is located precisely in this prefrontal region that is well developed only in human beings.

Human memory is a complex phenomenon, however, and of course involves other regions of the brain as well.

(Brain Stem! Brain Stem!)

SHORT-TERM MEMORY- Part 2

LONG-TERM MEMORY
Baddeley’s model of working memory has proven especially fruitful for research on the brain areas involved. This model posits a central processor that coordinates the activity of two sub-systems. Many brain-imaging studies show high activity in the frontal lobe when this central processor is working.

Source: NIMH Laboratory of Brain and Cognition. Published in Nature, Vol 386, April 10, 1997, p. 610
For example, the image shown here was produced by functional magnetic resonance, a technique based on the increased blood flow to the most active areas of the brain. In this image, taken while the subject was holding an image of a face in his memory, the yellow area in the prefrontal cortex is very active.

But Baddeley’s model also postulates the existence of a phonological (acoustic and linguistic) memory and a visual/spatial memory (containing mental images). Brain imaging studies have also revealed distinct neuroanatomical bases for both of these forms of memory.

The phonological loop activates certain areas in the left hemisphere that are associated with the production of language, such as Wernicke’s area and Broca’s area. Visual/spatial memory seems to be associated with a region of the occipital cortex generally associated with visual processing.

Meanwhile, certain sub-regions of the prefrontal cortex are activated only if the memorization exercise is somewhat difficult for the subject, thus confirming the coordinating role of the central processor.
Things get even more complicated when you consider the chronological sequence of memorization: the various steps involved in storing and retrieving a piece of information.


LONG-TERM MEMORY

The hippocampus, the cortical structures surrounding it, and the neural pathways that connect them to the cortex as a whole are all heavily involved in declarative memory–the memory of facts and events.

For example, after you’ve had a fine dinner with some friends, your memories of their faces, the taste of the wine, and the music that was playing are distributed in the various visual, olfactory, and auditory areas of the brain, but they are all connected together by the hippocampus to form an "episode", rather than remaining a collection of separate memories.

The hippocampus thus plays a fundamental role in episodic memory, the kind that will let you remember this especially pleasant dinner party years later. In fact, it seems to be the hippocampus that enables you to “play the scene back”, by reactivating this particular activity pattern in the various regions of the cortex. This phenomenon would be very important during dreams, and would explain the incorporation of events from the last few days into them.

But after a while, these various cortical regions activated during an event would become so strongly linked with one another that they would no longer need the hippocampus to act as their link. 

Thanks to this linkage, the memory of a piece of music that was playing that night could be enough to bring back the entire scene of the dinner party. Each of these elements could act as an index entry that lets you retrieve all the others to your consciousness.

Thus, information that has been encoded in long-term memory for a lengthy period of time no longer requires the intervention of the hippocampus. This is the case in particular for general knowledge in semantic memory, which instead activates the frontal and temporal cortexes. The activity in the temporal lobe would correspond to the activation of the fact in question, while the activity in the frontal cortex would correspond to its reaching consciousness.

Unlike our memory of facts and events, however, our spatial memory appears to be confined to the hippocampus. And more specifically to the right hippocampus. This structure seems to be able to create a mental map of space, thanks to certain cells called place cells.

Some very intense personal memories that bring what is sometimes called emotional memory into play appear to involve another structure of the limbic system besides the hippocampus. This structure is the amygdala, which is already known to manage our reactions to fear. Many other structures in the limbic system also help to encode our long-term memories.

Lastly, procedural memory, such as knowing how to ride a bike, does not appear to involve the hippocampus at all. Instead, procedural memory appears to be associated with modifications in the cerebellum, the basal ganglia, and the motor cortex, all of which are involved in motor control. As evidence to this effect, procedural memory is not affected by amnesia caused by lesions to the hippocampus, but is affected by damage to the cerebellum and by neurodegenerative diseases that alter the basal ganglia, such as Huntington’s disease.


But wait! There's more... BRAIN STEM! BRAIN STEM!

SENSORY, SHORT-TERM AND LONG-TERM MEMORY

Sensory memory is the memory that results from our perceptions automatically and generally disappears in less than a second. It includes two sub-systems: iconic memory of visual perceptions and echoic memory of auditory perceptions.  
Short-term memory depends on the attention paid to the elements of sensory memory. Short-term memory lets you retain a piece of information for less than a minute and retrieve it during this time. One typical example of its use is the task of repeating a list of items that has just been read to you, in their original order. In general, you can retain 5 to 9 items (or, as it is often put, 7±2 items) in short-term memory.

Working memory is a more recent extension of the concept of short-term memory. As techniques for studying memory have become more refined, it has become increasingly apparent that the original conception of short-term memory as a mere temporary receptacle for long-term memory is too simplistic. In fact, it is becoming increasingly clear that there is no strict line of demarcation between memories and thoughts. In order to test some hypotheses that may provide a better understanding of this complex phenomenon, the concept of working memory has therefore been advanced.

Working memory is used to perform cognitive processes on the items that are temporarily stored in it. It would therefore be heavily involved in processes that require reasoning, such as reading, or writing, or performing computations. One typical example of the use of working memory is the task of repeating a list of items that has just been read to you, but in the reverse of their original order.

Another good example is the task of simultaneous interpretation, where the interpreter must store information in one language while orally translating it into another.

Working memory appears to be composed of several independent systems, which would imply that we are not aware of all the information that is stored in it at any given time. For example, when you drive a car, you are performing several complex tasks simultaneously. It is unlikely that all of the various types of information involved are being handled by a single short-term memory system.



Copyleft
The content of  this post - All About Memory - is under copyleft.

The concept of "copyleft" is a method of providing free access to the results of original work and of encouraging people to reproduce and even modify this work on an equally free basis.

Copyleft is thus diametrically opposed to the traditional concept of copyright, which nowadays people seem to be trying to use to cover absolutely everything, from genes to intellectual property. In the libertarian spirit, the concept of copyleft promotes freedom of expression and staunchly opposes the idea that knowledge can be the private property of a small elite. So, feel free to copy or link to the contents of this post for noncommercial use.

BRAIN STEM! BRAIN STEM! ...make it stop....



Comments are welcome.




3 comments:

  1. Sorry, this looked too serious for tonight so I went back and sang along with Brain Stem, Brain Stem!!

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  2. Excellent post Lee. That one line of "it is becoming increasingly clear that there is no strict line of demarcation between memories and thoughts" is very interesting. It rather reinforces my idea that we have one vast file cabinet in our head (along with other things!).

    I did find it a bit odd that they said sensory memories disappear in a few milliseconds. If that's the case, how is it we can remember the feel of the wind on our face etc? Did I miss something?

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  3. Thanks for the comment Eileen.

    Excellent question on sensory memory. It is my understanding they are referring to the actual lingering perception of the feeling, like the burning sensation on your fingertip, rather than the memory of that pain.

    So... the feeling of the wind on your face lasts only a fraction of a second, but the memory of that feeling persists...

    Do you remember what your shirt felt like against your skin a second ago? Now you do ; )

    I hope that helps.

    Thank you,
    -Lee

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