WPT University Place Wednesday Nite at the Lab  Hilary Gerstein, "Do Older Elephants Ever Forget?"  March 2, 2011 UP560   cc >> Tom Zinnen: Welcome, everybody, to Wednesday Nite at the Lab. I'm Tom Zinnen. I work here and the University of Wisconsin Madison Biotechnology Center and for UW Extension Cooperative Extension, and on behalf of our other sponsors, Wisconsin Public Television and the Wisconsin Alumni Association, thanks again for coming to Wednesday Nite at the Lab. We do this every Wednesday night, 50 times a year. Tonight I'm delighted to introduce to you Hilary Gerstein. She's currently in the neuroscience training program here at UW Madison. Her interests focus on using rodent models to explore how cellular and molecular changes in the brain relate to behavior. Hilary has done past work with transgenic mouse models of Alzheimer's disease and also studied the effect of pharmacological manipulations on maternal behaviors and histology in mice. Currently as a graduate student she's studying the function of certain genes expressed in the hippocampus that have previously been implicated in learning and memory. In the Berger lab they use recombinant adeno-associated virus, otherwise known as rAAV, as a gene delivery system to over-express or knock down function of these candidate genes in specific regions of the brain. 

Hilary will then examine the resulting phenotypes with a variety of behavioral tests and anatomical techniques. Whoa, I like that.  Hilary gave this talk at PLATO Frontiers in Life Sciences last fall. I think you're really going to enjoy it. Please join me in welcoming Hilary to Wednesday Nite at the Lab. [APPLAUSE]  >> Hilary Gerstein: Is this on? Yes? Okay. It's really impossible to tell from here. Okay, so one of the nice things about the introduction that Tom gave is it wasn't just what am I doing now but it's what did I do in the past as well, because there's only going to be a little bit of what am I doing now. There's going to be several sections of this talk. I hope everyone got a chance to look at the cartoon because cartoons are awesome. 

There will be more cartoons. So this is where we're going today. First we're going to talk about memory, and it's kind of what I like to think of as information everyone should know about memory and how the brains works. Just basic overview. And then when we talk about that, you'll be prepared to talk about happens in the brain, what changes occur with aging and how does that relate to learning and memory. And once we have that down then we can look at some different ways in which aging can affect learning and memory. And we'll first start off with some theories about how Alzheimer's disease works. That is perhaps the most famous example of a disease involving aged individuals and learning memory deficits. And then lastly we'll look at some of the research I'm doing now in my graduate career in terms of what changes are going on in the brains of normal individuals as they age that causes their memory to change or not be quite as good. So it's a little bit of everything, but I think those are the best kind of public talks so you get a little bit of everything and not just too much detail on any one thing. 

And you can raise your hands and ask questions as you like. Okay, so the first thing is that memory is not all just one thing. There's different types of memory, and that's actually really functionally important to know the difference between the different types of memory. So first we have short-term memory or working memory. And this is if someone tells you on the telephone, oh, you need to call this number, you need to call the restaurant to make a reservation, let me tell you the number. And then you look around for a pen, and you can't see a pen so you start repeating the number to yourself as you walk around your home looking for a pen so you can write it down. That's a type of working memory, short-term memory. It could also be if you sit down or are cramming for something very last minute and then right it all down within a few short hours. Long-term memory is, as it states, long term. And there's two major types of long-term memory. 

First is conscious memory or declarative memory. And this is facts. So people, places, events, what year William the Conqueror invaded Normandy, D-Day, what your grandmother looks like, what your birthday is, any of these things are facts. That's conscious or declarative memory. Unconscious or procedural memory is different. That's something like riding a bicycle, for example. Once you have learned or acquired the task of riding a bicycle, when you get on a bicycle you don't think okay I'm going to move my legs like this and I need to stand up straight and balance, it just sort of happens. It's unconscious. And these, as you'll see in a bit, are the important in terms of how they are different. So interestingly, both short-term or working memory and conscious and declarative memory show a gradual decline or aren't quite as good in individuals that are aged. 

And that's just a normal event. That doesn't mean there's anything wrong with the individual. It is something that happens pretty much across the board. But what's even more interesting is that specifically the conscious or declarative memory is greatly impaired in certain forms of dementia and also in also Alzheimer's disease. So this is the type of memory we're going to be looking at today. We're going to be looking at long-term memory for facts, people, places, events, things. Okay, so something I always like to start off with is we're going to talk for a while about how your memory is going to get worse but first let's talk about how your memory can be improved. So memory palaces, this is actually very fortuitous because there is a book coming out, I think it comes out this week by Jonathan Foer and it's called, I have it written down on the next slide I think, Moonwalking With Einstein. It's about how he trained himself using this exact method I'm going to explain to you right now to become a national memory champion. And he started investigating this because he wanted to write a newspaper article about it. 

And then he got sucked into the competitive world of memory games and became a national memory champion himself not having any previous experience with it. So it does work. It can work. Let's explain. This is a tool by the ancient Greeks. Not everything was always written down. It was very expensive to have scribes. So it was very common for important people in the learning community to memorize works of literature or science. And the way, one way you can memorize something very large like a string of numbers or an entire book is to your spatial memory. So they developed this thing called a memory palace, and you think about a building that you know incredibly well. 

I like to use the house I grew up in. My husband likes to use the Metropolitan Museum of Art in New York because he grew up near there as a child. Something that you know very well, you can imagine yourself walking through it in three-dimensions in your mind's eye. And as you go through the palace in your mind's eye, you deposit the little items that you need to remember. So if I'm trying to remember a long string of numbers I'm going to think about walking in the front door of my parent's house where I grew up, and what do I do next? I would take out my keys and put them down on the little bowl where we have the keys, and that's where I would leave the first number in the string I was remembering. Then I probably take off my shoes, and so I look down and, look, I would put the number in my mind's eye, number two, on top of where my shoes are right inside the door. Then I would probably walk to go let the dog out of his crate, on top of the crate I would leave the third digit. And you can actually leave a trail of the numbers or the objects that you were trying to remember throughout this entire palace, and all you need to do to retrieve them is take the same path through your memory palace. And you can train yourself to be very effective at this. And, in fact, one of the most famous world memory champions has used this method repeatedly for eight national championships or eight world championships. 

And he can use this exact method to memorize 1,000 random numbers at over 300 locations, and he can commit them all to memory in half an hour. That's pretty extreme but I've personally used memory palaces to remember, like, eight numbers, and that works pretty well for me so I was excited about that. [LAUGHTER] Starting small. >> They do that only with numbers? >> So, you can do it with anything, but the common tasks that you have to complete to become a world memory championship are often things that don't have a lot of meaning so they're difficult to remember. So strings of random numbers or the order of a deck of cards are common things that they use. Things that are very emotionally salient like JFK being shot, like where you were when you found out about the buildings falling in 9/11, those are not things you have to struggle to remember, they are very emotionally salient. So to really test these people's memories they want to use something that is not emotionally salient at all. So the memory champions are using an interesting piece of information about the brain is that they're using the hippocampus. And the hippocampus is important for this because it is required for both the conscious declarative memory that I just mentioned that's important for facts, places, long strings of numbers. It's also required for spatial memory. 

So when you are navigating in space such as in a house, even if you're not physically in the house just walking through the house in your mind's eye, or if you're trying to remember facts, strings of numbers in both cases you're using your hippocampus. So it makes sense that the memory palace would work because it's sort of a combination of conscious declarative memory for facts and memory for a space. Additionally your hippocampus is important for taking short-term memories and changing them into long-term memories. And if you have your hippocampus removed for some reason, then you no longer have the ability to make new long-term memories. And you'll talk about that more in a minute. So where is the hippocampus? It's the sort of blue C-shaped guy right there. It's in your temporal lobe. And so if you were to put your hands right about here just underneath your skull in your temporal lobes on either side of your brain. And it's, as you can see, quite small. It is not a large part of your brain at all, but it's very important. 

So the discovery of this role for the hippocampus in declarative memory owes a great debt to an individual who used to be known as patient HM, but he died a few years ago so now we can use his full name which is Henry Molaison. And Henry had a childhood head injury and also a deep family history of epilepsy, and this led to common blackouts and more than one major or grand mal seizure per week in his late 20s. That's a lot of seizures, and that made his life very difficult for him. So as was common at the time and still occurs, they treated these seizures by removing the part of the brain where the seizures emerge from. And for him, that was the medial temporal lobe which included the hippocampus. So they removed the entire medial temporal lobe and both hippocampi from Henry Molaison. And, as you can imagine, they didn't know this at the time but when testing him afterwards when he came out of surgery and was recovering weeks later they discovered that there has been one striking and totally unexpected behavior result: a grave loss of recent memory. And I don't mean that he couldn't remember his childhood, I mean that he couldn't make new long-term memories. So after the surgery, anyone he met he would be able to talk with them for a brief period of time, if they got up and left the room for more than a minute and came back in, he would introduce himself to them all over again. And he had no ability to maintain memories for more than a few minutes, at most maybe half an hour. 

So if anyone has seen the movie Memento or 50 First Dates, that's actually somewhat accurate in terms of the type of memory loss this individual went through. And as you can imagine it's pretty devastating. So to look at exactly what they removed from HM you can see here the red sections where they've removed a good half of the hippocampus, the medial or the inner part. It's actually quite a significant amount of tissue they removed. So most of the really interesting work performed on patient HM was done by a researcher named Brenda Milner at the McGill University, and this was back in the '60s when they were first starting to understand the role of the hippocampus in learning and memory. And something that she really ingeniously figured out is that patient HM didn't have a loss of all memory. He only had a loss of conscious or declarative memory, that memory for facts, places, people, events. His unconscious or procedural memory was still in intact. And the way she discovered it was this is she had a task which was pretty common in neurological testing called a mirror tracing task. And as you can see on the screen there's a star and what the individual has to do is their hand is placed into a box and they look forward into a mirror and they can only see their hand in the mirror and based on the image of their hand in the mirror they have to trace the star. 

So if you've ever done this, it's incredibly difficult because you move your hand this way but the image moves that way. And it's really disconcerting, it's very difficult to control. And if you practice it enough over multiple times, you get good at it like any other motor task you need to learn, like riding a bicycle, like writing in cursive. If you get used to it, you get good at it. In HM's case, over the course of several days she would present this task to him and have him do it. And each time they would ask him, do you remember having done this before, have you ever done a similar test before? And he would say no I've never done this before. Even on the third day when he sat down and did it perfectly, expertly, he said, I've never done this before, I guess I must just be good at it. So he had no memory of performing the task, of the fact of performing the task, of the event of performing the task, but he had learned it his procedural or unconscious memory. So the hippocampus is this area that we're talking about right now, and I want to show you a little bit more about it. So if we zoom into the blue C-shaped item over there, and then we take a cross section through it, what you see is this big image right here. 

And you can see it's not just a mish-mash of cells. There are parts of the brain that don't have a lot of structure to them, that just look like a big blob, but this is not one of them. It's a highly structured part of the brain, and it has specific layers of cells that are arranged in a very specific pattern. And the neurons in one part of the hippocampus can project to and make connections with neurons in other parts of the hippocampus. And this way they form a complex or an intricate circuitry. And that circuitry is thought to be responsible for how we encode memories. So how do the cells communicate with each other? How do the neurons in the hippocampus communicate? So first we have a sending neuron, and it's going to be sending an electric signal which we call an action potential. So it's sending its electric signal down the long part of it, which we call the axon, and this is kind of the long telephone wire that reaches out and connects to the next neuron in the chain. And at the end of the axon it gets close to the receiving neuron that's going to receive its signal, but it doesn't actually touch the receiving neuron. The space between the sending neuron and the receiving neuron is called the synapse. 

And when the electric signal reaches the bottom of the axon in this sort of large area called the terminal, it will trigger chemicals to be released from that sending neuron. And these chemicals are called neurotransmitters because they transmit a neurological signal. These chemicals can then flow across the gap and bind to special receptors on the surface of the receiving neuron. The receiving neuron can then take that signal and use it to do a whole host of things inside the cell including its own electric signal down its own axon and continuing the sort of whisper down the lane effect. Okay, so how does this relate to memory? Well it's thought that new memories are encoded by changing the pattern of synapses. So how much neurotransmitter is released by each electrical signal can change. You can have some synapses that are very strong that will release lots of neurotransmitter. You can have some synapses that are very weak and don't, and this pattern of which synapses release neurotransmitter when and how much is what we think encodes memory. So, again, how does this relate to aging? Well, there is evidence of shrinkage of the hippocampus in certain old people. Not all elderly persons have a shrunken hippocampus, but those that do been found to perform less well on certain memory tasks, especially memory tasks that involve spatial memory. 

So when I was a technician at the lab I'm going to show you the research for in a minute, one of the graduate students would visits individuals in the Alzheimer's ward, and she would take them on a specific route around the hospital and then show them pictures of landmarks from that route and ask them to explain where they saw it. And individuals with smaller hippocampi are impaired at this task compared to older individuals with larger hippocampi. So that's one clue as to how the hippocampus could relate to memory and aging. Another one is that there seems to be evidence for changes in the number of synapses, in the strength of synapses and what molecules go into make up synapses in elderly people. So it's been found that age-related changes in the expression of certain genes and those genes encode certain proteins that make up the synapse could be important for learning and memory. And that's the research I'll show you at the end. But in the meantime, I'm going to first show you some theories of Alzheimer's disease now that we have a sort of good overview of what the different types of memory are, why the hippocampus is important for the type of memory that is often deficient in older populations. And now we're going to talk about the hippocampus and its role in the most famous example, in my opinion most famous example, of an aging related memory problem. Okay, so some people, unfortunately, are not diagnosed with Alzheimer's disease as early as would be useful in order to start treating them right away because the early behavioral symptoms are kind of vague. Forgetfulness, irritability, depression, confusion. 

That could come from a whole host of different causes, and in the later stages of Alzheimer's we get changes in personality and most famously the inability to encode new information. So those are the behavioral problems, but what are the physiological symptoms? So the physiological symptoms include neuronal death, and that neuronal death usually starts at the hippocampus which explains some of the memory problems that we'll discuss in a minute. But if you can see this picture, we have a nice healthy brain on the left-hand side, nice and full, and on the right-hand side with an advanced Alzheimer's individual there's a shrunken-ness of the cerebral cortex which is all the dead neurons being sloughed off. And as you can see where the hippocampus that I've circled in blue is on the healthy individual, there's just nothing there on the Alzheimer's individual. So you can see how that would affect learning and memory. Okay, so there's many, many theories as to the cause of Alzheimer's disease, but these are two of the most highly researched theories. So I thought I would explain a little bit about them and how they might relate to each other. So the first theory is called the A beta theory. And it goes like this: so there's a large protein on the cell membrane in neurons called APP, and it's very large. And in order for its parts to go off and do their jobs in the cell, they need to be cut down into smaller pieces. 

And one of those smaller pieces is called A beta, and you can see it in purple. Now if you have a lot of APP that needs to get cut down, the enzyme that cuts isn't quite as accurate. I mean, if you're being rushed and you are have a lot of work to do, you might not be as accurate either. So in this case there's so much APP that it's not cut very accurately, and the APP that does end up being cut is too long, and this long abnormal A beta is toxic. And it aggregates or just forms into clumps that we know of as plaques. So what do plaques look like? So here on the left we have a slice of healthy brain tissue from a human being, and the little purple dots are cell bodies and they look nice and healthy. And on the right we have the similar cell bodies in purple, but we also have these large brown plaques and a lot of them. So that is what tissue looks like with A beta plaques. Now the Tau theory is a little bit different. Tau is a very important protein that allows neurons to communicate. 

First we should go over the parts of the neuron. So we have the cell body which is the large part of the neuron. Like any cell it has a nucleus. And the dendrites are the areas where the cell will receive information from other neurons. Then we have that long axon, that long protruding axon I mentioned previously, and that's where the outgoing information will go from our cell here to the next cell. So Tau is very important because it holds together the axon, the physical structure of the axon, it holds it together the way railroad ties hold together a train track. And if you've ever, you know, seen an old movie where a train is going to go off the tracks because someone has sabotaged the railway and ripped the ties off, it's kind of like that. So if Tau is not there to do its job, the axon will literally break apart. And as is common with many cell types, if the cell can't do its job, if it can't communicate, it will die. So this is an image right here of axons, and if there's two many phosphate groups, if the Tau becomes hyperphosphorylated, then it can no longer hold on to the axon and it falls off. 

Without this structural Tau holding the axon together, it just falls apart, it spreads out and it dissociates and then we have neuronal death. Additionally, those hyperphosphorylated Tau proteins cluster together or aggregate into tangles. And so we can also see this visually just by inspecting the brains of individuals of a certain age. So on the left we have healthy brain tissue. It looks lovely. And on the right we can see that in the stain that is staining for axons or axonal proteins, we can see that there's a lot of business there which is the Tau tangles. So I've just explained a little bit about the A beta theory, and I've explained a little bit about the Tau theory, so the question is which one is it? So let me show you some evidence for each. So the gene that encodes the protein APP is found on human chromosome 21, and many of you may realize or already know that Down syndrome occurs if an individual has three copies of chromosome 21. So those individuals with Down syndrome, besides having Down syndrome, also have 50% more APP than a normal individual, and people with Down syndrome almost across the board develop Alzheimer's disease by the time they are 40. So this is some evidence for A beta and APP being very important in causing Alzheimer's. 

Additionally, they've looked at the brains of elderly people, some elderly people that were starting to get forgetful but they died, some elderly people that were really just mentally sharp until the day they died, and they saw differences in the number of Tau tangles in these individuals. The individuals that were very, very sharp had very few Tau tangles and they had a young looking brain, according to researchers. Whereas individuals that were getting more forgetful, maybe a little bit of a dementia, had many Tau tangles. So this is some evidence for Tau. So which one is it? If you perform histology, if you look at the brains of individuals with Alzheimer's disease, you'll actually see both forms of pathology. So it's thought that both may play a role but many, especially 10 years ago, many researchers who investigate Alzheimer's disease tend to favor one over the other, tend to concentrate their lab looking at either Tau or looking at APP. And this brings me to my cardinal rule of science number one, which is when some scientists say that something is caused by A and other scientists say that something is caused by B, it's pretty likely that both might be involved because scientists are smart people and they probably both have evidence in both cases. So let's consider both of them together. But especially a number of years ago this was a delicate matter. People would fight about this and squabble. 

So the lab I was in before I started graduate school where I was a research technician wanted to prove just that, that both of these proteins I just explained to you might play a role in Alzheimer's disease. So this is the title of the paper, but what you need to know is that we looked at special mice with Alzheimer's disease. However, mice don't get Alzheimer's disease. So we have to give them the human APP gene so that they can then have Alzheimer's. This is a very common model that we use for Alzheimer's, and these mice show the same behavioral symptoms and they also show this same physiological symptoms in their brain as humans with Alzheimer's do. So we gave the human APP gene to certain mice, and, happily for us, all mice expressed the Tau protein. So that was already there. So the question is, oh, so we also, to make things interesting, knocked out the Tau gene from some mice. So we have mice that have APP but no Tau, mice that have Tau but no APP, and mice that have both. So the question is, do mice with APP and Tau have worse or better memory than mice with just APP or mice with just Tau? How do these two proteins work together to affect the memory in these animals? So what we did in order to investigate this is we used the Morris water maze. 

And the Morris water maze is a great task because it's very dependent on the hippocampus, and it uses that spatial memory I was talking about that is one of the main roles of the hippocampus. So what the animal does, so rats and mice are both very good swimmers. They don't like being wet, especially if the water is a little cold, but they're very good at it. They can do it very well. And so we put the animals in this tank of water, and we have a hidden platform somewhere, and when I said hidden I mean that the platform is just under the surface of the water so they can't see it. They have to just swim around and find it. The first day or two that we're testing them, that we're training them on this task, there's a large flag or something really visually obvious sticking out the top of the platform saying here it is. So they can just swim directly to that nice visual cue, get on to the platform. Their feet are still wet but they don't have to be swimming, they're not soaked in the cold water anymore. And they like that, that's a reward for them. 

 So they learn to do that. They learn to swim to the visual cue, and then we take the visual cue away. And now they have to use visual and spatial cues around the room. We tend to hang up a lot of things on the walls to try to make it easier for them. They have to use their spatial memory to remember where that platform is, and we can drop them at different places around the edge of the pool. And by the end they will learn where the platform is and swim directly to it no matter where we drop them because the platform is always in the same place. Okay, a graph. I know, I will take you through it. So on the left we have escape latency. So what we're learning or what we're measuring here is how long did the mouse swim. 

How long did it take this mouse to find the platform and escape from the water. So that's what we're looking at in seconds on the left. And then on the bottom it's just what day of training are we on. We have five days of training. So this is time. And if you can sort of see the colors, I don't know if you can, but there are six different groups, and there's three groups that are red, and they're sort of at the top, and there's three groups that are black, and they're at the bottom. The groups that are black don't have any APP. They don't have Alzheimer's. The groups that are red at the top have APP. And for each of those having APP or not having APP we have having two copies of the Tau gene, one from the mother, one from the father, one copy of the Tau gene or zero copies of the Tau gene. 

This is a Tau knockout. And so what we see is that all three groups in black, if they have two copies of the Tau gene, one copy of the Tau gene or zero copies of the Tau gene and no APP, they all learn well, and by learn well I mean their escape latency or how long it takes them to find the platform goes down every day, and by the last fifth day it's quite low, it's 10 seconds or under which is quite good. However, when we look at the animals that are expressing APP, that do have Alzheimer's, we can see a difference that's caused by the amount of Tau they have. So at the top we have animals that have APP and two copies of the Tau gene, and they're at the top with the red boxes and the solid line. And then performing a little bit better than them are the animals with APP and Alzheimer's disease, and they only have one copy of the Tau gene. And then performing at the last day almost as well as the animals with no APP are the animals with APP and no Tau. So this is very interesting. It seems that the more Tau the animals have, if they have APP, the worse they do. So after the last day of training, we do something really sneaky with the water maze, and we take the platform out. So now there's no way to solve the maze, and it's really mean but it's important. 

So the mouse needs to swim around for the entire minute, the entire 60 seconds and we track what path he swims. So on the left we have an animal with no APP and two copies of the Tau gene. So this is a very normal mouse. And a normal mouse by the end of the fifth day you drop him in the upper left-hand corner and he'll swim straight to the quadrant that has the platform, and he'll just swim around, swim around, I know it's here somewhere, I know it. And he'll keep doing that very religiously. However, an animal that has the APP gene and a full amount of Tau, both copies of Tau, we'll place him in and he kind of swims haphazardly around the entire pool. You can see he would have eventually found the platform, his little path crosses the little platform box at one point, but he's not very confident of his answer there. He's swimming everywhere. And then if we look in an animal that has this same APP but no Tau, we can see that he's performing quite well. He's really sticking to right near where that platform was, very similarly to the animal that had no APP. 

So, what did we learn here? So lowering the amount of Tau or knocking out Tau completely from animals with APP who are a mouse model of Alzheimer's disease seems to make them smarter. So this is interesting. But I just said that lowering the Tau expression in mice with APP makes them smarter, but it doesn't change the way their brains look at all, which is weird. If you saw behavioral changes, you want to see structural changes in the brain to go with it, but you don't in this case. So if you look at, if you can see the top and the bottom, at the top row of three pictures we have a picture of the cross-section of the hippocampus similar to the one I showed you before, but now glowing green are all those little plaques that we talked about before, all those clusters of APP. And the same thing is in B, it's just that it's not green, they're brown. I don't really see much of a difference between the animals with APP expressing lots of Tau who were very stupid and the animals with APP expressing no Tau who were smarter. There's not really any difference. They both have a lot of plaques, and that's a lot of plaques especially compared to a normal wild type animal in the lower left-hand corner that doesn't have any plaques. So what's going on? Let's review. 

So mice that express the APP gene get Alzheimer's disease. Okay? Mice that express the APP gene but do not express the Tau gene, have had the Tau gene knocked out, do a lot better on memory tasks. Okay, that's cool. And mice with APP always get plaques even if their memory isn't so bad and regardless of how much Tau they have, which is very interesting. So what does this mean? So it mean that is both APP and Tau need to be present to have both types of Alzheimer's symptoms. They need to both be there in order to have the plaques and in order to have the memory problems. Yeah? >> Is there a possibility to move the Tau and the plaque response are a reaction to a different level of perhaps a low level inflammation of the brain, and somehow the plaque and the Tau just simply respond to that? The reason I'm saying this is on the way over here I heard on the news that seniors who take a low level dose of ibuprofen had a significantly lower level, 40%, of developing Parkinson's disease. And ibuprofen, of course, is an anti-inflammatory. So is there any relationship between the inflammatory response in the brain system in the development of Alzheimer's? >> So that's really spot on and very interesting. So it's totally possible that both of these events might be caused by a third item that doesn't have a obvious thing to look at. 

Like plaques, I see them, they're right there, let's find what causes them, that's probably what causes it. Inflammation is generally thought to result from the A beta. There's been some experiments that show even before the plaque formation that just the higher levels of APP and A beta result in inflammation which, of course, can change how the brain is and make it more susceptible to further insults as well. So it's kind of this beautiful vicious cycle in a lot of ways. And, yes, inflammation in general can make the brain susceptible to a lot of diseases, but then the diseases can also make the brain more inflamed. Okay, but so yes so this feeds right into what I was saying. So what does this mean? A beta plaques are correlated with Alzheimer's disease, but they may not be causing the disease on their own. And this is fairly new. Like 15 years ago no one was really thinking that. So one of the other things I was working on in that lab was to test a new plaque busting drug, and these plaque busting drugs were shown to go in and just blast apart those plaques which everyone thought would be great because there's these big ugly plaques in the brain, let's just get rid of them. 

But actually we found that this made the mice even more stupid. This made them worse. And that wasn't really expected, and it depended on how long after the drugs you tested them, how long a course of the drugs they had, what dose of the drugs they had, but we found that it was thought that breaking those plaques apart released the toxic A beta so it was free to float around in the brain. And so there's a new theory which is that collecting the toxic A beta protein into these plaques is kind of the brain's way of gathering up all the mess and just kind of making dust piles as it sweeps around, like trying to condense the areas of damage. And so just spreading someone's dust piles all over the house is just going to make everything dirty all over again and actually be worse. So the take-home message from this is my cardinal rule of science number two is that correlation is not causation and that even scientists jump to conclusions sometimes. Dr. Alzheimer's met a woman with severe memory problems, and when she died he looked at her brain and it was full of plaques. And so scientists have been assuming for many, many years after that that these plaques must have caused the memory problems, but it may not be direct causal relationship. And so this is one of my favorite comics on that topic. So it's important to remember that just because something is correlated, it might not be the cause. 

And everyone loses track of that sometimes, but it's important to keep it in mind. Okay, so the last thing that we're going to talk about now that we've talked about general ideas of what memory is, we've talked about how aging can affect memory, and we've talked about one very clear example of disease in terms of aging and memory. We're going to talk more now about normal changes in memory that might occur during the course of aging. So here's a little spiel about what might be happening in normal aging in terms of gene expression. So by gene expression I mean DNA that is being read into RNA and then being made into protein. And the protein is the tool of the cell. It can go around and perform lots of jobs. So in babies and teenagers and young individuals different genes are expressed in their brains than an adults. And the same is true for the elderly. Different genes are expressed in their brains than in adults, which is very interesting. 

So we found that certain genes are expressed more in adults than in the elderly and certain genes are expressed less in adults than in the elderly. What's also interesting for us is that this phenomena of genes being expressed differently in the elderly is not just in  humans. It's also true in many mammals, for example, rats and mice. There are old rats that are just very, very old but they still learn and remember just as well as young animals. And that's great. And there's some old rats that are incredibly demented, and they don't have any one particular disease or problem, they're just really not with it anymore. And that's kind of similar to humans. Some individuals age incredibly well in terms of their ability to learn and remember and some don't. And so we're interested in what genes are responsible for that. So my lab previously performed a gene expression study to look at what genes in the rat are changing or have changed in elderly individuals, and we can use that to get a good idea of what might be changing in old humans because humans and rats are actually fairly similar. 

So the gene that I personally work on is called Homer 1, and there's different forms of Homer 1. There's Homer 1B and Homer 1C and Homer 1A. And they're found all over the brain, but since we're talking about learning and memory we're just going to talk about the hippocampus today and keep it simple. So we found that after a learning task or a memory task such as the Morris water maze I just showed you, animals, old rats, had an increase in their Homer 1C levels if they were smart. So we took all the animals that were old that learned the task really well and looked at their brains and their brains had more  Homer 1C in them. And we took all the animals that didn't do terribly well on the task, that didn't remember very well, and their brains did not have very much more levels of Homer 1C. They had fairly low levels of Homer 1C. So maybe these old rats were learning impaired because they didn't have enough Homer 1C. Okay, so we were not the first individuals to think to look at the behavioral effects of the Homer 1 gene. Actually another lab knocked this gene completely out of a strain of mice. 

And they found that these mice had a whole host of symptoms including small body size, they're really tiny. They have poor motor coordination. They have an enhanced social drive. They are also really anxious and kind of crazy, very twitchy. But most important for us, they feature significant learning deficits. And another group took some healthy rats, just totally normal rats, and injected the Homer 1C gene into the hippocampus. And they tested those rats against normal rats, and the rats with the more Homer 1C did better. So imagine if I could take you and crack open your skull and inject something into your hippocampus and then you'd be smarter. That's what they did. That doesn't happen a lot. 

That's really cool. So this raises the question if we restore specifically the Homer 1C form to the hippocampus of these knockout mice, will it help their problems that our hippocampus based, and we know that the hippocampus is important for declarative memory and spatial memory. So would it fix their problems in spatial memory? So that's what we're finding out. So in this experiment since we're using mice we did not use the Morris water maze which was developed with rats in mind, we used the radial arm water mace which is very similar in that the animal is in a pool of water. There is a platform that they need to swim to. The platform is always in the same place. First the animals are trained to swim to a platform with a large visible cue sticking out the top. And then we take the visible cue away, and they have to use spatial cues around the room to remember where the platform is. However in this case there's sort of arms, it's not just a big open circle, there's arms or lanes it can swim down. And this makes it a little bit easier for the mouse, and it's easier for us to record their behavior because now we're looking at the number of errors they make and each error is any time they swim down an arm that does not have the platform. 

So if he swam into three arms that didn't have the platform and then swam down the arm with the platform and found the platform, that'd be three errors. So let's look at some of the data. So on the left-hand side we have the number of errors they made or the wrong arms they entered. And on the bottom again we have the trials that we performed or time. So the two groups that I'm showing here are both Homer 1 knockout mice. However, the red ones at the top have had Homer 1C injected back into their hippocampi. And we used a viral vector as Tom mentioned in the introduction. We use rAAV as a viral vector to deliver our little gene package into the brain because viruses are very good are going in and injecting DNA into cells so we said, hey, you want to do that for us? And they did. So we have animals that, so these are both Homer 1 knockout animals, and in red we have Homer 1 knockout animals that we added Homer 1C back in the hippocampus. And in green we have Homer 1 knockout animals that we've added green fluorescent protein to their hippocampi. 

Now you might ask, why did we do that? That's not going to help them learn, it's just going to make their brains green. And that's true, but it's very important to have proper controls. So we wanted to make sure that there was a group of animals that were treated the same as our animals injected with Homer 1C that were genetically identical, they're also Homer 1 knockouts and they've undergone the exact same brain surgery and the exact same recovery period and the exact same experience of having a virus in their hippocampus, but the gene that is expressing is just green and it's not a gene that's going to change how their synapses work which is Homer 1C. So this is a great control. And if we look at how these animals perform, we can see when there's a visible platform, which is the first four dots, both of these animals are decreasing the number of errors they make each time. So they're maker fewer and fewer errors. They're getting better and better at the task. However, when we move to the hidden platform, so we take away the visible cue, both of the animals have an uptake in the number of errors they make because I just changed everything on them, that's kind of sneaky, but the animals expressing the GFP just kind of flat line. They're not really getting better very much anymore. Whereas by the end, the Homer 1 knockout animals that have had Homer 1C put back into their hippocampus are performing significantly better than the animals without Homer 1C. 

And this difference is significant which is awesome. And if you want to see what this looks like compared to a normal animal, we took the litter mates or the brothers and sisters of our Homer 1 knockouts that are genetically normal, and we ran them as well. And you can see that they have a similar learning curve on the visible platform, they're not thrown off as much by the change in the paradigm. And by the end you can see that Homer 1 knockout animals where we've added the Homer 1C back to the hippocampus, they're performing almost as well as their wild type brothers and sisters, which is super cool. So to sort of review what I just showed you, we have these Homer 1 knockout animals where we've added Homer 1C back to their hippocampus. These mice perform significantly better on a task of spatial memory, which we know to involve the hippocampus, than the Homer 1 knockout animals that were just expressing GFP, they were just green. So basically injecting Homer 1C into Homer 1 knockout mice fixed their memory deficits. And you might say, well of course, they were lacking it and you gave it back to them, of course that would fix it. No, not of course. Not of course at all. 

In fact it is very, very difficult and rare to be able to fix a knockout animal by giving them back the gene later in life because if you think about it, their entire embryological development, their entire childhood and in most of their adulthood they've lacked this gene. Their brain has come up with other methods for doing what needs to get done. And then you're adding this tool, this protein back in, and the brain hasn't ever seen that before. It may not integrate, it may not have a use for it anymore. So being able to do this kind of gene therapy in animals in a knockout animal and get it to fix the deficits is really cool and not all that common. So what we can say here is that if there is a lack of Homer 1C, we added it back to the hippocampus and it made the animal have a better memory. So how does this relate back to aging, which we had been talking about for the entire rest of the talk and then I started talking about young animals. So this experiment took younger animals in mid-adulthood that were lacking the Homer 1 gene and it added the specific Homer 1C form back to the hippocampus. And this helped the hippocampus recover its ability to make memories. So previous research in our lab showed that learning impaired older animals had very low levels of Homer 1C. 

So the next question we wanted to know is can we add Homer 1C to the hippocampus of these old learning impaired animals and will it help them too? Or maybe it's too late for it to have an effect. We don't know. So stay tuned because I'm going to be starting that experiment next month. [LAUGHTER] And that's the end. This is a picture of me and Brenda Milner who did all of that really seminal work on HM, and I've been to rock concerts where there have been fewer people swarming the main event afterwards. She had body guards, and there were at least 5,000 people swarming this 90-year-old woman who had just stood and given an hour lecture on her feet in her nice high heels. And she's awesome. So a round of applause for her. [APPLAUSE]