Lecture 7 - Episodic and Semantic Memory 2 Flashcards
Explain what you know about consolidation.
● Semantic and episodic memories are subject to a consolidation period, a time window during which new memories are vulnerable and easily lost
● Consolidation: the process of strengthening the stability of stored information. - Stabilize memories
- Incorporate new memories with old ones
- Different types of consolidation (we will start with one type)
Next week we learn more about “consolidation” –for now you just need to know it means that memory traces (“record”) become stable.
What are the 2 theories associated with episodic memories and the hippocampus?
Two current theories, though no clear answer yet:
View 1
Standard Consolidation Theory
(sometimes known as Standard Model)
View 2
Multiple Trace Theory
these theories are about the role of the hippocampus.
patients with amnesia also have trouble learning new facts about the world. She told us last class that patients have a lot of problems remembering episodes from their past but see mto have an okay time remembering facts. The first theory is called the standard consolidation theory. Sometimes known as the standard model. This is about what happens to old memories. The second view is called the multiple trace theory.
What is standard consolidation theory?
The hippocampus is involved in the encoding of episodic or semantic memories but its involvement fades with time, as memories are stored (“consolidated”) in the cortex
according to this theory you should treat episodic and semantic memory as the same. Because their role is short lived, you would expect to see some sparing of older memories in amnesia. If you look at the image on the left, what is being depicting is the hippocampus and the cortex. You can see that there is some connection between the two. What you are seeing is that overtime the hippocampus fades. Overtime you only have cortical, cortical connections. Its importance or involvement fades overime as memories are stored and consolidated into the cortex. The alternative
What is the multiple trace theory?
The hippocampus is involved in the encoding of episodic and semantic memories but its involvement in semantic memory fades with time, as memories are stored (“consolidated”) in the cortex BUT the hippocampus continues to be involved in episodic memory in perpetuity
this is the alternative theory. There is a distinction between episodic and semantic memory. This theory differs from the other in the fate of episodic memory. They agree on what happens to semantic memory but not what happens to episodic memory. The initial acquisition is hippocampal cortical and for episodic memories, there remains a necessity for the hippocampus to be involved. Why is it called the multiple trace theory> when an event is experienced it can be stored as an episodic memory, but it postulates that each time to the memory is retrieved you are reinforcing that episodic memory and that could be why it stays hippocampal.
● According to multiple trace theory, when an event is experienced, it can be stored as an episodic memory by a group of neurons in the hippocampus and the cortex
● Each time that memory is retrieved, the retrieval itself becomes a new episodic memory “trace”
LOOK AT GRAPHS ON SLIDE 10
we have theories that allow us to make predictions about what the data is going to look like. We are seeing birht up until today on the y axis you have number of memories recalled or the detailedness of the memories. She divided this into anterograde and retrograde. The distinction between retrograde and anterograde amnesia is where the onset occurs. Both sides look the same in the gray. Here you are seeing what we expect to see. She would only ask us to draw the prediction for episodic memory because the theories look the same for semantic memory. What you see in the blue section is something interesting. As controls continue to decline overtime, the amnesic patients have a little bit of amnesia right before the onset of amnesia but they look normal from adult to birth, They look indistinguishable from controls for remote/old memories. So anything that occurred after or just before the onset, you get an impairment but the rest have been spared. This is because according to the theory the memories have already been moved to the cortex. There’s only one difference with respect ot the multiple trace theory. It doesn’t matter how old or new the memory is, they will always be at floor because the hippocampus is damaged and the hippocampu is always needed for episodic memories.
What do amnesia studies say about the two consolidation theories?
● Earlier studies show data consistent with view 1 (standard consolidation theory), which shows “temporally graded” amnesia, but later studies show data consistent with view 2 (multiple trace theory), that is, “flat” amnesia.
we now know the theories, we know what they predict, what does the data say? earlier studies show data consistent with view one meaning temporally graded because it depends on where in time you are looking. Many studies show this pattern. Later studies show data consistent with view 2. We call this a flat amnesia. We have a bunch of data supportive of theory one and a bunch of data supportive of theory 2. Different labs show different patterns, the problem is we don’t know if there are different methodological factors that play a role. Earlier work in HM shows the temporally graded amnesia. Later studies refined the methodologies. Sometimes patients old memories are remembered stories (over rehearsed and looks like there is a lot of detail), The researchers tried to sample lots of memories from that time period. Does HM have an intact remote memory? The researchers were really careful to use sensitive measures that really just honed in on just the episodic details .Details specific to an event, HM’s memory was a flat line. So in the same patient we have one pattern vs another pattern. At this point, some researchers believe strongly in one theory and others lean strongly in the other. If you ever find yourself researchering memory loss you want to go in with a really open mind.
How do we reconcile the findings about the two consolidation theories?
How Do we Reconcile the Two Sets of Findings?
Trace Transformation Theory is a newer theory that posits that all memories are initially stored as detailed, episodic memories in the hippocampus, but as time passes, memories gradually become generalized and less detailed, eventually being stored in the cortex as more semantic-like.
Older memories that are transformed might remain intact after hippocampal damage, leading to graded amnesia.
Older memories that are not transformed will be impaired after hippocampal damage, leading to flat amnesia.
some researchers developed follow up theories to put these 2 theories together. She will not test us on trace transformation theory. She wants us to know about it because it helps us understand the line between the 2.
WATCH VIDEO FOR SLIDE 13
WATCH VIDEO ON DEVELOPMENTAL AMNESIA. TESTABLE
this is the big picture, an MRI image zoomed in and arrows pointing to the hippocampus. This hippocampus is quite small. We can tell this because there is lots of empty space aroudn the hippocampus. The percentage of volume loss can range. It seemed to be the case that the rest of the brain looked spared. It seemed to be selective hippocampal damage. Then you have the 3 patients depicted in the case seires. One change we make in terms of language is the term “normal” controls. Instead we say “neurologically intact” controls. Thats whats happening in the hippocampus. What about their memory performance? Participants are shown a figure that doesn’t look like anything they’ve seen in their life. We ask them to copy it. We can see that they are able to draw it in the first place. We wanna know that people can percieve it and their perceptual abilities are intact. They copy it and then it gets put away. After a 3 or 20 minute delay, participants are asked to do the drawinf by memory. THeir perceptual abilities are not different from the control. BUT their memory is quite impoverished. This is a test of episodic memory because you have to retrieve that memory and produce it.
this is the big picture of the article. All we need to know is that they did neural imagine (structural imaging). The purpose of taking pictures of the brains
what we learned in this article is that individuals acquired hippocampal damage early in life. The most interesting cases is there ones where the damage was sustained around the time of birth. These folks 2/3 experienced loss of oxygen during the perinatal period. This can happen in premature babies. Often times it happens during the birthing process, a lack of oxygen for a period of time which can lead to damage ot the brain. It can affect the hippocampus. One reason for this is that it has high metabolic activity. It is sensitive. What happens is these individuals have early hippocampal damage and their brain damage went undetected. No one noticed. They grew and developed, they entered school around 4-5 and it was at that time that teachers and parents started to notice that something was a bit off wit htheir memory.
