Memory: Types of Long-Term Memory

I really need to find a way of opening these that isn’t ‘And we’re back’.  I’m working on it.  Be patient with me, I’ve only been 18 for three days – I’m not used to decision-making yet.

There are a few types of Long-Term Memory – three, to be exact, and they’re split into two categories.  That sounds like it confuses things, but once you get the hang of it, it actually makes the topic a lot easier.

Those two categories are explicit memories and implicit memories.  Explicit means that they come from the things around us, whereas implicit means that they’re ingrained into us.  The types of explicit memory are episodic and semantic memories, whereas the type of implicit memory is procedural memory.

Episodic Memories are our memories of events that have happened.  When you remember something that’s happened, you usually remember the context, like what you were doing before and after the event.  You might remember the time and place, and things like what the weather was like, and you might remember the emotional context, or how you felt.  For example, I can pinpoint the ambulance ride after I broke my leg.  Before the event, I was cycling in my grandma’s drive.  After the event, I was lying on a stretcher in a big white room whilst people came and looked at the leg.  I remember that it was early August in the morning, and that it had been raining, and I know that I felt terrified, but that I was also just a tiny bit excited.

A semantic memory is knowing something like a fact, or common knowledge.  For example, by making this blog, I am contributing to both your semantic memories and my own semantic memories.  However, a semantic memory can also be something like knowing how to behave in a certain situation, like knowing that you should shake hands when you meet someone important for the first time.

Researchers have shown interest in whether semantic memories are all formed through episodic memories, or whether a semantic memory can form independently of an episodic memory.  Research on patients with Alzheimer’s Disease who are unable to form episodic memories has found that they are able to form semantic memories, which suggests a dissociation between the two types of memory.  However, researchers also look for a second dissociation, as it is otherwise possible that the brain struggles with episodic memories because they place greater demands on mental functioning as a whole.   In this case, a second dissociation has been found, in which patients with the same disorder have generally in tact episodic memories but poor semantic memories.  This suggests that semantic memories may be able to form independently of episodic memories, but that there is an association between the two.

Finally, you have procedural memories.  Procedural memories are knowing how to do something.  These are processes like tying your shoelaces, making tea, or even walking along.  Generally, you don’t think about procedural memories when performing them, and doing so makes them slower.  They are automatic memories learned through repetition and rehearsal, which means that we can focus on other things whilst we do them.

Brain scans have shown that different areas of the brain are active when different types of long-term memory are being used.  For example, episodic memory is associated with the hippocampus and surrounding parts of the temporal lobe, whilst semantic memory is associated with the frontal lobe and procedural memories are associated with the cerebellum.  All types of long-term memory are thought to induce some level of activity in the hippocampus.

HM, who we talked about when we went over the Multi-Store Memory Model, was actually able to form long-term memories – but only procedural ones.  He was able to learn how to draw a star from looking at its reflection (not an easy task – certainly not something that I could do, and I don’t have any brain damage!), but had no memory of actually learning how to do so, which would be episodic or semantic.  However, we have already discussed the issues with using a brain-damaged patient as evidence, and this problem occurs a second time when one considers the fact that we cannot know exactly which area of the brain has been damaged until the patient has died, which means that they may have damage to a relay station in the brain, for example, rather than a unitary store in the brain.

There may also be a second type of procedural memory, called priming.  This is based on the idea that if you show an individual a picture of a banana and ask them to name a colour, they’re likely to respond with ‘yellow’, because they have been subconsciously primed to think of yellow by the yellow fruit.  This is called the Perceptual-Representation System, and it is separate from episodic and semantic memories, and is present in those with damage to their episodic and semantic remembering.

That’s a wrap on the types of long-term memory.  I feel a little bit like I whizzed through that, but I don’t think it’s too unclear.  Any questions, as always, can be posed to me in comments.

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