Memory Formation Circuitry

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From the course by The University of Chicago

Understanding the Brain: The Neurobiology of Everyday Life

624 ratings

The University of Chicago

Understanding the Brain: The Neurobiology of Everyday Life

624 ratings

Learn how the nervous system produces behavior, how we use our brain every day, and how neuroscience can explain the common problems afflicting people today. We will study functional human neuroanatomy and neuronal communication, and then use this information to understand how we perceive the outside world, move our bodies voluntarily, stay alive, and play well with others.

From the lesson

Abstract Function

You've now learned an incredible amount about the way the brain functions to perceive and act upon the world we live in. You've gained an understanding of neurobiology on a cellular level, and how many diseases and disorders of the nervous system can affect our bodies and minds. In our final module, we will journey into the realms of emotion, attention, memory, and language. By the end of this module, you will have a greater understanding of the more abstract cognitive functions the brain.

The Story of H.M.5:00

Memory Formation Circuitry6:41

Hollywood Amnesia6:45

Clinical Amnesia5:45

Meet the Instructors

Peggy Mason
Professor
Neurobiology

[MUSIC]

So what we talked about in the last segment is that what HM taught us is that

the temporal lobe, the front part of the temporal lobes on both sides

are required for declarative memories.

Let's look in at what are the structures in the front of the temporal lobe.

And the required structure for

memory formation is a structure called the hippocampus and it sits about here.

And this is called the hippocampus.

It's a type of cerebral cortex.

It is not neocortex, it's a three layered cortex, and

neocortex is a six layered cortex.

So the hippocampus is an old

type of cerebral cortex.

And let's just take a look at it.

Here is the hippocampus in all of its glory.

This is, actually let's go back.

We're gonna look at a section through here, and

what you see is just the front bit of the temporal lobe.

And right here, this bit, is the hippocampus.

Okay, so what does the hippocampus do for memory?

Well, remember that we have two different types of declarative memory.

We have semantic memory and episodic memory.

In order for both of these types of memories to be formed,

so they're going from working.

So working memory to become long-term memory that requires the hippocampus.

Without the hippocampus, one or the other, this is not gonna happen.

Neither semantic memories nor new episodic memories can be learned.

And HM, in fact, learned no new episodic memories.

He didn't ever learn a new event.

He didn't know who was president.

And he also didn't learn semantic events,

he didn't learn semantic memories, so

he didn't learn new words like psychedelic,

he didn't learn about new celebrities,

Ronald Reagan remained for him an actor, not a president.

And so no new memories can be formed, either semantic or

episodic, without the hippocampus.

Now once we get to recall, let's say the memory has been formed,

in both situations the hippocampus ships that information out to the neocortex.

The neocortex is all of this.

We've seen many pictures, all that outer rind of the brain, that's all neocortex.

Okay, so the memories get shipped out to the neocortex.

In the case of semantic memory, that's where it stays.

It never has to go back to the hippocampus.

It is stored in the neocortex and that's all it takes.

So if you lose your hippocampus, you do not lose your old semantic memories.

And this was really well illustrated

by the account of Jill Bolte Taylor.

She is and was a neuroscientist and

she had a hemorrhagic stroke in the middle of a post-doctoral

fellowship that she was on, and she recovered remarkably.

She recovered so much that she was able to actually write this book which

tells talks about her amazing journey back from completely being debilitated.

And she not only wrote the book, but

she narrated the audio book in a delightful way, which is what I listen to.

But in it what she tells of is that there was

one section of semantic memory that she lost.

It was just gone, never to be returned, no glimpse of it again.

And that was math.

So the interpretation is that her hemorrhagic stroke actually

killed a piece of her neocortex, and that piece of the neocortex

that was killed was the part that stored all that mathematical memory.

Okay, so let's get back.

So semantic memory made in hippocampus, stored in neocortex,

all we need to get it back is to reaccess that neocortex.

As long as that piece of neocortex is alive we're good to go.

Episodic memories are different.

They're again, made in hippocampus and they're stored in the neocortex, but

to access them we actually send them back to the hippocampus for

re-consolidation, and then they come back to neocortex.

Well, so you might wonder, is the memory.

If this memory gets shipped out to neocortex, and

then this memory gets shipped back to hippocampus,

does it come back to neocortex in exactly the same form?

And I think Ulric Neisser's experiments tell us that the answer is no.

Every time it goes through this loop the memory can be changed.

So there are no absolutes in memory and this reconsolidation,

this circuit that episodic memories continually go through,

upon recall it gives us a mechanism by which every time we recall it,

we can change it a little bit, or not.

But this is probably the reason why memories are so labile.

Okay, in the next segment we're gonna look at what does a loss of memory mean?

What is an amnesic patient?

[MUSIC].

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