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  University of Idaho
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  Psychology Dept.
  University of Idaho
  Design - P&D  CTI

The first major theories of memory go way back to the time of Aristotle and Plato.  But for us, the first major theory of memory that we talk about was developed by Atkinson and Shiffrin called multiprocess or stage theories.  In essence, what stage theories or multiprocess theories basically say is this:  We have some kind of sensory experience (whatever that is) and again, it can be visual, auditory, or even tactile.  That information then goes into what we call a Sensory Memory system.  In the sensory memory system (that we see in slide three), the sensory impressions are stored in a form similar to the original sensation.  There are lots of different types and subgroups.  The first of these subgroups is shown in slide four and is called iconic memory.  This memory type is related to structures and memories that we have within the visual system.  So, what I’d like you to do is look at an object somewhere in your room and just focus on it for a minute.  Now, that you’ve focused on it I want you to close your eyes.  What do you see immediately after you close your eyes?  Guess what, the structure’s still there for a very short period of time and then it fades.  These are examples of what we call iconic memory.  In general, iconic memories last about a quarter of a second but they can last longer.  Now why do we get that?  Well, the reason we get iconic memory is because of the processing that’s going on in the eye with the bipolar, ganglion, amacrine, and horizontal cells in the retina of the eye (which used to be part of the brain in early evolutionary organisms).

Another type of memory system that we talk about in sensory memory is shown in slide five.  That is called echoic memory.  Echoic memory is related to the auditory system because of sounds that last in the cochlea and temporal lobe.  They last longer than iconic memory because what you have in the basilar membrane vibrating in your cochlea.  As a result, it continues to have some kind of sensation and causes action potentials.

So now, what we have as we go back to slide two, is some material in iconic memory or echoic memory.  Basically it’s in some kind of sensory memory system.  Now, as we see in slide two, two things can happen.  The first thing that can happen is that nothing happens.  As a consequence we forget it.  Think about that, we have lots of different sensory experiences that we see out there from our eyes, but we don’t remember every little piece of it, (at least most people don’t).  Instead, what we have to do is pay attention to some kind of particular stimuli.   If we do pay attention to those particular stimuli, we move into the next system which is what we (see in slide six) call short term memory.

Short term memory basically consists of two components:  Events that occurred which are still in our consciousness, (which I just talked about a second ago), or information from events that are brought back by recall from long term memory.  So, if we go back to slide two and look at it again, the information in our short term memory can do one of three things.  We can, number one, rehearse it.  If we rehearse the information in short term memory, it remains in short term memory.  Or number two, we can forget it.  If we forget it, it just goes away.  Or number three, it goes into long term memory.  So, let’s talk about how long this information and how much of the capacity there is in short term memory system. 

The classic studies that we’ll talk about short term memory (how long, much information we can keep in short term memory, etc.) was done by Miller with Bell Labs.  Basically what Miller showed is that you generally store seven plus or minus two pieces of information in short term memory, and that it lasts a relatively short period of time.  Why do you think the telephone number that you normally dial consists of seven digits?

Well, once this information is in short term memory, and it’s rehearsed or not forgotten, it then moves into the next particular system that we call long term memory.  The question then is, “What is the duration of long term memory?”  The answer seems to be, once you get information stored in long term memory, it lasts forever.  The classic example of this was done by Penfield, the great neurosurgeon from Canada.  What Penfield basically did was pioneer a technique called neuromapping.  What he would do was when he was doing brain surgery, is he take little dots, put a number on them, and he would put these dots on different parts of the brain.  To understand what particular brain structures were involved, he would provide small amounts of electrical stimulation to the patient (who is conscious during all of this because the brain has no sensory receptors).  The patient would then tell Dr. Penfield what was going on. What Penfield found was that when he examined or touched certain parts of the brain (and it didn’t matter where it was), the patients would recall with great detail and clarity memories that they had had in their early childhood which they had forgotten for 20, 30, or 40 years.  So it seems, once you get the system material into the system you basically keep it in there forever.

So that’s really the first theory of memory.  Later theories of memory expanded on this model.  Instead of short term memory, they made a change to what we call working memory. Working memory relied (as we see in slide 11) on a computer model.  What we have from a computer some kind of sensory input.  That sensory input is for the most part, a key input from a keyboard.  That information then enters some kind of working memory (which we in a computer world called random access memory or RAM).  Finally the information is stored in some kind of storage system (today, usually on a hard drive).

So, the major difference between the stage theories of memory and later theories of memory basically relates to working memory.  In essence, it’s not really a storage system but it’s a capacity to store with information.  For example, if you don’t have enough RAM in your computer what happens?  It crashes.  Well, the same thing occurs with working memory.  You put too much information in at one time, and the system doesn’t remember anything.  It forgets a lot of stuff and, in essence, it crashes. 

Now, there are a lot of different classification schemes related to memory.  As we see in slide 12, there are lots of different types.  Several of these types are shown in slide 13.  That is, information is going to go from sensory into short term, and then into long term.  Once we have this information in long term, it’s going to go to a variety of different memory systems.  Primarily this long term system is made up of two major systems; procedural memories and declarative memories (which consists of semantic memories and episodic memories). 

As we see in slide 14, there are a lot of different memory types.  (Which I’ve just described in the previous slide).  So, what are these different types of systems and different types of memories?  The first of these, as we see in slide 15, are what we call episodic memories.  These are memories for specific events.  What happened, where did it happen, etc?  For example, where were you when the Challenger blew up?  Or, where were you when 9/11 happened. Or, where was your first kiss, or things like that.  All of these are very specific episodes that we have in our life.  Each of them is related to specific memories that we have.

Declarative memories on the other hand (as we see in slide 16), are memories for particular items that we have knowledge of and it’s independent of the way that we acquire them.   In essence, declarative memories are basically the sum of all your acquired knowledge. All the works, the facts, words, appearance, objects, schemas, all those things we have that’s out there is basically related to declarative memories.

Now, a third memory system we have are called visual memories or what we call idectic imagery.  These are what you call in layman’s terms, photographic memories.  Some individuals can retain and recall very detailed images of visual scenes for long periods.  However, it is very rare.  For example, only 5% of kids ever have it, and it’s significantly less for adults.  The reason for that is that kids rely more on imagery than adults. 

So now we’ve talked about a variety of different types of declarative memories.  What about procedural memories.  Well procedural memories are (as we see in slide 18) memories that we have for physical things.  The classic example is riding a bike or using the gearshift or the stick-shift on your car.  So, let’s say that you’re starting to learn how to use a standard type of car transmission.  Now, you’re getting in the car with a stick shift and you start to drive.  What happens with the clutch?  Well, what happens is that you grind the gears, you stop, and you break inappropriately, and on and on.  But after you’ve done this for a period of time, you start to get better at it until you don’t have any problems with doing this.

Ok, so now we’ve talked about different types of memory systems.  Well, in the past these are the systems that we used.  Today, however, we expanded upon these a little bit and tried to give it better detail.  So, we have changed the way that we think about memory systems into what we call implicit memories or explicit memories (shown in slide 19).  Implicit memories basically involve reflexive behaviors or procedural skills.  The recall of the information is unconscious.  For example, you don’t remember everything that you do to throw a baseball or hit a golf ball.  It’s also very rigid.  And it’s connected primarily to the stimulus conditions where the knowledge was particularly learned (such as a golf course).  Explicit memories, on the other hand, are basically the knowledge of people, places, and things.  It’s recalled again, as you can think about it, like a deliberate, conscious effort.  However, it’s highly flexible and it oftentimes involves multiple pieces of information.  Again, as we see here, it consists of two different groups:  episodic memories and semantic memories.  On slide 22, we’ve kind of put this into two major groups.  So again, it gives us a different look at what we have in relation to memory systems.

Now there are a couple of different types of implicit or non-declarative memory.  Some that we’ve talked about (procedural memories); however, there are two other memories that we really need to make sure we understand.  One is associative learning which we relate to classical conditioning and operant conditioning.  The other is non-associative learning which relates to habituation and sensitization.  If you don’t know what these are, I suggest that you go back to your basic introductory psych book and look these up again.  They’re basically the relationships between how stimuli work within our environment.

Well we’ve talked now about a variety of different types of memory systems.  What are some structures that are involved with memory?  As you can see on slide 23, there are a wide variety of different structures.  I have then taken these structures and placed these on slide 24 where they go within the particular systems.  As you can see, some particular structures go with things such as habituation and sensitization, while others are involved in the medial temporal lobe. 

Let’s talk about some of these pathways for a second.  Let’s talk about explicit memories first.  Again, these are going to begin in association cortexes which we’ve talked about before.  That information is going to go into what we call the parahippocampal and the perirhinal cortical structures.  These then continue into entorhinal structures and then into the hippocampal formation, going back to the entorhinal structures, and then back to the parahippocampus, and then back to association corteces.  So again, what we have is a variety of different structures that’s involved. 

What about the entorhinal cortex? What is it and where is it located?  Well for the location you need to go to figure 15.8 of Carlson.  But the key is it’s getting its information from a variety of different structures; from association cortex, from the fornix, from the amygdale, and other structures.  In essence, it’s going to send this information via the dentate gyrus to the perforant pathway.  Basically that’s the major pathway to getting information from association cortexes to the hippocampus.  Also, these are the structures that usually begin to get damaged when we started to develop Alzheimer’s. 

Another major structure that’s extremely, extremely important in memory is what we call the hippocampal formation.  It includes a variety of different structures of which I’ve listed on slide 27.  Basically, the slide is going to include material from a variety of different structures, from where it gets input, and then sends output.  Again, the structure is extremely important for the formation of new memories.  As we can see here, I’ve included a slide that shows where the hippocampal anatomy is and where the particular structures are.

In general, the hippocampus, as we see in slide 29, plays an extremely important role in coding and storing information.  When you damage this structure, you have extreme difficulty recalling information.  The reason is that it wasn’t encoded appropriately into the system.  So, when you damage it, you don’t get new information stored very well, but the old information remains intact.  An example might be you are doing fine, having a good life, etc.  You have a stroke, your hippocampal formation is damaged, and you cannot recall any new information.  So, whatever you learned prior to that is what you have.  This is called anterograde amnesia and it can be very debilitating; especially if you take the person and move them to a new location.  Where do they always go, back to the location where they were before the stroke.

One of the major neurotransmitters that are involved in the hippocampus is Achetocholine (ACh.)  Basically, when you block ACh. you get disruption in working memory.  Again you can antagonize that, and reverse the effects.  So what you often see today are a variety of different new drugs coming out designed to increase the production, or increase the uptake or increase the way receptor sites are being used with ACh.  And, a lot of new drugs are being used right now trying to decrease the effects of Alzheimer’s and other types of memory disorders.

However, there are a lot of other structures that are important in relation to memory as well.  One of these is a structure we’ve talked about before and that is your thalamus.  The thalamus (as we see in slide 31), is thought to give the message to print the memory initially.  So, if you damage the structure, there is no memory trace even to begin with.  Ultimately it’s neither stored in short term memory or in long term memory.  So, in summary, if you damage the hippocampus, the memory forms, but because of elaboration problems, you don’t encode it. When you damage the thalamus, you never get any kind of memory formation at all. 

Well, what are some other structures that are involved?  Another major structure that’s involved in memory is the cerebellum.  The classic example of cerebellum being involved with memory was done in some studies by Thompson.  What Thompson did was condition an eye blink response and a leg movement response using classical conditioning.  Then, he lesioned the area that disrupted the eye blink response.  When he did that, the leg response was unaffected.  But then he moved 1 mm closer to the middle of the brain and then lesioned that structure.  Guess what he found?  The conditioned leg response was affected but the eye blink response was not.  So, what he concludes (as we see in slide 34) is that isolated procedural memories have very distinct pathways in the cerebellum.  You also get the same kind of response when you damage or remove structures within the hippocampus. 

Now one other major structure that’s involved in memory is the cortex.  We’ve talked a little bit so far about different areas of the cortex having involvement with different types of systems.  Well, guess what?  The same kind of thing goes on with memory as well.  The cortex seems to be very, very related to the type of memories that’s involved and most of this is done in the frontal lobe.  However, a lot of different motor memories are also highly loaded in areas close to the motor cortex, while other types of sensory memories seen to be very influenced and loaded in areas in the parietal lobe close to the somatosensory area.

I’ve put together an overview about some of these particular structures.  This is shown in slide 36.  Again, the information is going to go in the sensory memory.  The reticular activating system and the thalamus is going to have very, very important roles in paying attention and taking that information and putting it in short term memory.  We’re then going to put that information in short term memory.  If we want to store that information in long term memory we have to use the hippocampus.  Once we get that information going in the long term memory, it’s stored either in the cortex, the cerebellum, or other related structures.

So, in conclusion, when we talk about memory, we talk about memories from a wide variety of different systems and using different structures.  When one damages any of these structures, it will cause different types of memory disorders.  We are going to talk about some of those disorders at the end of the class.  So, now we’ve talked about a variety of different systems within the nervous system.  In the next section, we’re going to begin talking about how that upper brain system communicates with those other peripheral systems.  That is, through the spinal cord.  So until we get to that section, we hope you’re having a good day and we will talk with you soon.