I want you to think about what you did yesterday. Where did you go? Who did you hang out with? What was the weather like?
What were you wearing? What did you have for dinner? Now even though you can't see it or feel it, there's a lot of neural activity occurring in a region of your brain known as the hippocampus that right now is trying to retrieve those experiences and combine them into a cohesive memory.
Now there's a lot of uncertainty about how this process works and what we're going to do in this video is try to unravel it and break it down. So, let's get started. Alright guys, welcome to Psych Explained. Before we get started, don't forget to hit that subscribe button.
Now in this video, we're going to break down the hippocampus, a part of your brain that plays a key role in memories. But, as I stated in the introduction, it's not that straightforward. There's still a lot of debate in the field.
about the relationship between memory and hippocampus. Like how does it actually form new memories? And most importantly, where are memories actually stored in the brain?
We'll touch on those topics in this video. So let's dive in. Now the first thing I want to draw your attention to as our labeled hippocampus, which is this long tube-like structure, is where is the hippocampus actually located in relation to other structures? And this is always a good opportunity to practice our four major lobes. So let's practice.
We have our frontal lobe, which sits right in the front of the head, our parietal lobes, which sits right on top of the head, our occipital lobe, which sits right in the back of the head, which leaves our last lobe, which sits right on the side, right by our ears, which is called our temporal lobes. So what does that tell us? That is the location of our hippocampus, deep within our temporal lobes. Now notice that I said deep within.
In other words, if you're just holding the brain, you wouldn't be able to see the hippocampus. right, as you would see like the auditory cortex which is on the outside, but rather you'd have to slice through the temporal lobe and look towards the center in order to locate the hippocampus. Now another way to look at this is that this is our left hemisphere, right, the person's facing towards me you could tell with the eyeball. This only tells half the story.
We also have a right hemisphere which sits on the other side. So what does this mean? It tells us that we have two hippocampus. We have one located deep within our left medial temporal lobe and we have one located deep within our right medial temporal lobe.
So we have a hippocampus located on each side. Now what else do we know about the hippocampus? Even though it's its own isolated structure, it's part of a larger set of structures in an area of the brain known as the limbic system.
Okay, we'll have another video on the limbic system as a whole, but this is the limbic system. And what do we know about the limbic system? Well, this is an area of the brain that's primarily responsible for three functions, emotions, memories, and drives. Now, what structures make up the limbic system?
You have the hippocampus, right? That's the structure for today that primarily deals with memory. We have the amygdala, which is this almond-shaped structure.
It sits right here. That is probably the emotional part of the brain, the emotional memories. We have our hypothalamus that sits around here.
That primarily controls our... endocrine system and our autonomic functions and the thalamus as well. And there's a few other structures, but that would be our limbic system. Now, how do we know what the hippocampus does? We've talked about this in other videos, but oftentimes you have to observe damage to that area, right?
Whether it's an animal, whether it's a human being, and then you observe what are the effects. Now, for our purposes, I want us to think that there are two major types of amnesia, okay? What are those?
Let's think about this. Imagine that this orange rectangle right here represents the event of the injury. Okay, so this is going to represent the event. This could be research, right, where you lesion or remove that area of the brain in an animal, or maybe it's a traumatic injury of a human being and their hippocampus is damaged. What else do we know?
Imagine that this line represents new information. Okay, so going this direction represents new, and this direction represents old. So what does this mean?
Well, if you have damage to your hippocampus, we find is that you might not be able to create new memories. Okay, what do we call this? We call this anterograde.
Interograde amnesia. Okay, now what do we know about interograde amnesia? One of the most famous case studies in psychology revolves around a man by name of Henry Molaison or H.M.
In the early 1950s he suffered from seizures, so doctors removed his medial temporal lobes to alleviate those seizures without realizing what the hippocampus actually did. or at least its full function. Now H.M.
was able to recall things from the past, maybe his childhood, but he wasn't able to form new memories, specifically episodic memories. Those are memories of your or life. So you might ask HM what he did the day before he couldn't remember. So that is one type of amnesia. Let me make sure I got that right, which is unable or unable to create new memories.
Now what about old information? Well what if you can't remember anything before the event? This is what we call retrograde amnesia.
Retrograde amnesia. Now, I'm not referring to, let's say, childhood events right before the event. That you might still have intact.
But in the weeks or months leading up to the injury, those are the events that you might not remember. A nice way to remember it is the word retro means backward or past. So we have anterograde amnesia, which is unable or unable to recall or make new memories. And you have retrograde, the inability to recall old memories. Anterograde and retro.
All right. What does a hippocampus actually do? In this video, we're going to focus on three major functions.
Let's talk about the first one. Now, the first major function is what we're going to say, the formation of new... Memories. Formation of new memories.
Now let's break this down. What do I mean by memories? I want you to understand, not all memories are the same.
Remembering how to ride your bike is a different type of memory than than remembering all the countries in the world that start with the letter S, right? In other words, one revolves around a habit or a skill, the other one takes a lot of conscious effort. So what does that tell us? It tells us that the hippocampus is responsible for a specific type of memory. What type?
Well, we're gonna call this explicit or declarative memories, okay? Declare, declarative memories, okay? Or as I said before, you could say explicit.
These are the type of memories that you really have to think about, right? To consciously recall. Like I asked, what did you do the day before, right? Yesterday. That would be an explicit declarative memory.
Now we can divide this into two types. There are episodic memories, right? Those are the memories of your life.
Those autobiographical memories, episodic memories. And you also have memories of facts and dates. We call these semantic memories.
These are memories of, you know, general knowledge about the world. So we have... formation of new memories, declarative memories specifically, which can be divided into two types, episodic and semantic.
Now, how can we remember this? Now, for each function, what we're going to do is think of a scenario. Here's our scenario.
You just went on a date with somebody. So you're in the middle of a date. You had a great time. You went to the movies.
You went to dinner together. Now, realize it's not that the memory is being formed after the date. The memory is being formed while the date is occurring. So how would this work?
Well, every memory starts with taking in sensory information, right? We're taking in sounds and vision and somatosensory information and olfactory information and gustatory information. We're taking all this information in, okay? So imagine you're sitting at the table with your partner and you're going to the movies. What information are you taking in?
Let's do this together. You're taking in, for example, visual information, right? This would be our visual cortex, okay?
So this would be our VC or visual cortex. Now, what would you be taking in? Well, you might be looking at colors, right? Maybe the person's shirt or pants.
You might be looking at facial expressions, right? Anything that you can see, facial expressions, would be in the visual cortex. You also have your somatosensory cortex, which sits in your parietal lobe.
Remember, taking in sensory information, our somatosensory cortex. And this might be things like, well, maybe it's cold out that night, right? So you're encoding things like it's cold. Maybe you held hands at the end of the night.
Right, so you have that feeling, that touch. Okay, now what other sensory information are we taking in? We also have our auditory cortex, right? That sits in our temporal lobe as well.
There's our auditory cortex. And maybe you're listening to sounds of the person's voice, right? You have sounds, the person's voice, right? You're hearing all the, like, everything in the restaurant's very loud.
What's another sense? All right, so we also have our olfactory cortex. Okay, which will sit right around here. Now what do we know about our olfactory cortex? Well, olfactory is our sense of smell.
So think about everything you're taking in, right? Maybe you're at the movies and you're smelling popcorn, or maybe they're wearing some sort of cologne, right? This would be olfactory. So memories start with taking in sensory information.
We have vision and we have touch, somatosensory, we have sound, and we have our sense of smell. So where does the hippocampus play a role? Well, as all this information is coming in through our senses, All this information is linking and drawing a direct pathway to our Hippo campus.
Okay? All going... to our hippocampus. So we have some metasensory, we have our auditory, and we have our olfactory, okay? And the hippocampus is beginning to encode this information, okay?
In other words, it's temporarily storing this information, but it's also kind of combining this information into one unique memory, right? So in other words, when you remember the next day, you're not having five distinct sensory experiences, you're kind of creating this one unique memory. How cool is that?
That's essentially how our hippocampus works. And then later on, when you're trying to retrieve the memory, let's say the next day, the hippocampus is going to reach back to those experiences and help recall as well. Okay? So that would be our formation of new memories. What would be next?
Well, now that we have formation of new memories, what if we have to transfer those memories into long-term memory? We call this memory, did we get that right? Memory consolidation.
What do we call it? Memory consolidation. And I said before, what do we know about this?
This is turning short-term memories. into long-term memories. Now, one of the biggest misconceptions I see is that the difference between short-term and long-term memories is where they're located. It's almost like short-term memories are here, and then when they become long-term, they're located over here. But that's not how it works.
The distinction between short-and long-term memory is really the strength of those neural connections, the strength of all these experiences. Let's visualize this together. Imagine, for example, that these two neurons represent a lot of the neural activity involved in the formation of this memory on the first date.
This first neuron that sends the information is called the presynaptic neuron. So this is the presynaptic. And then the neuron that receives the information is the postsynaptic neuron.
So we have the pre and the post. And as you're thinking about the memory over and over and over again, what's going to happen is information from the presynaptic neuron is going to start to flow out. right our neurotransmitters between the synapse the synaptic gap and bind to receptor sites on the postsynaptic neuron now as you think about it over and over again what we have is more neural activity more neurotransmitters being released and more receptor sites opening up on these channels okay on these little knobs right here okay so in other words the strength of a connection is measured by how much change is in the postsynaptic neuron as a result of what the presynaptic neuron is doing.
So we have more neurotransmitters, we have more receptor sites opening, which is making the efficiency between these two neurons much better, which makes retrieval much easier. Now what do we call this? In psych, you might call this long-term potentiation.
Long-term potentiation. Sheation. Potentiation. There we go.
Or you could say LTP. Right? You could say synaptic plasticity as well. Right? This is the idea that there's actually a physical change in the brain as a result of learning something.
So how does this work? How do we actually combine this? Well, there's a lot of evidence that when you transfer something from short-term to long-term, the hippocampus doesn't really play a big role anymore.
Right? That's kind of one of the dominant theories. So let's say, for example, that instead of you're on a first date, it's three months later.
or four months later right now you're in a committed relationship with this person and think about how many times you've thought about this first date right everybody's been in committed relationship knows that when you think about that first date you've thought about over and over again well there's kind of a predominant theory that what happens is is that all these links all these memories all these connections all these experiences are going to start forming a network a neural network right between these experiences now we're not saying for example there we go that these are where memories are stored in the brain right that's kind of up for debate but the idea is that the hippocampus plays less of a role and when you're retrieving the memory a year later is that because you've thought about it so often, these memories in the neocortex are gonna fire immediately, right, and immediately retrieve that memory. So that's a nice way to think of long-term potentiation and the neural network that's gonna form, and hippocampus might not play a big as role as we think in those long-term memories. All right, what is our last major function?
Our last major function, we have formation in memories, we have turning that memory into long-term, is what we call spatial Spatial navigation or spatial memory. Okay? Or spatial memory. This is your awareness of your environment, right?
If you're able to close your eyes and think about your house, right? Or your apartment. Do you know where all the furniture is, right?
Do you know... How to guide your way through the house while bumping into things. Can you go to your the town you're from and be able to navigate where the streets are?
This is spatial navigation. And if you can close your eyes and visually represent it, we call this your cognitive map. This is specifically your cognitive map.
Your visual representation in your mind of a specific space. Now how do we know the hippocampus plays a role in spatial navigation? Well, there's a lot of really good research on this, specifically something called play cells.
Now, what do we know about play cells? Well, imagine, for example, that this rat is running this mace, right? We want him to run here and all the way to get the cheese. Well, what researchers are able to do is isolate individual neurons within the hippocampus and see that they only fire when the rat is in a specific location, right? Imagine you're in your bedroom.
The idea is that you have specific neurons that are firing that are different than if you're in your living room, right? So let's kind of visualize this together. Imagine we can isolate three neurons in the amygdala. This is going to be our amygdala.
We'll color one blue, we'll color one orange, and we'll color the third one, you know, purple. Okay? So as the rat runs the maze, researchers can actually see on a screen which neurons are firing. So the rat begins to run a race, and we see the blue neuron firing. right these action potentials and all of a sudden when the rat notices it's in a different environment as it's turned the corner a different set of neurons are firing okay different action potentials and then finally as it goes the it turns the corner a different set of neurons are firing And this is letting the rat know where it's located in space.
And this is a really good example, or at least some research, of how we know that the hippocampus plays a big role in spatial navigation or spatial memory. And if you think about how spatial navigation plays a role in our first dates, well, have you ever been to a restaurant for the first time and not know where anything is? Right, you walk in, you look around, you're very confused, you're looking for the bathroom, and all of a sudden you end up in the kitchen.
You're like, where am I? Well, imagine you keep going back to that restaurant on every anniversary, right? three years, four years, five years.
Over time, you're going to develop this cognitive map of the space. When you're looking for the bathroom, you're looking for the kitchen, you know exactly where to go. It becomes this kind of automatic memory.
That's a good example of spatial memory and hippocampus. All right, guys, thanks for watching. I really hope you took something away.
The hippocampus is such a cool structure. I like to think of it as a mental time machine because you can relive any event that you like. And by the way, if you're wondering why there was a seahorse here, that's because...
That's why we call it the hippocampus. The word hippocampus derives from the Greek word meaning seahorse because that's what it looks like. That might be a nice memory technique.
See you next time.