That Neuroscience Guy - Alzheimer's and Dementia

Episode Date: April 25, 2021

Dementia and Alzheimer's disease are prevalent and devastating conditions. In today's episode, we discuss the neuroscience of Alzheimer's and Dementia as it relates to their symptoms, causes, and prevalence. 

Hi, my name is Olof Kregolsen, and I'm a neuroscientist at the University of Victoria. And in my spare time, I'm that neuroscience guy. Welcome to the podcast. As we get older, we begin to experience any number of problems. Our bodies don't work quite the way we want them to. One of the more scary things that can happen to us is when our brain begins to fail us. As we get older, we might begin to experience mild cognitive impairment, which may then lead to dementia and potentially

one of its many forms, Alzheimer's disease. On today's podcast, we're going to talk about the neuroscience of dementia. As we age healthily, it's normal for our memory to fail us a little bit. But people with mild cognitive impairment and dementia typically have this to a bit further extent. For instance, they're not able to recall recent events or conversations, things that might have happened just an hour or two before. As we get older, we might, for instance, forget the name of a distant relative. But when we get dementia, for instance, we might have trouble knowing family members that we're actually close to. And the frequency of these problems increases. And that is typically one of the symptoms or signs of dementia or cognitive impairment.

So, by definition, dementia is characterized by a decline of information processing abilities accompanied by changes in personality and behavior. In other words, your brain begins to not function the way it did when you were younger and healthier. It's important to separate dementia from delirium, which is an acute disturbance of cerebral function. It's possible while experiencing delirium, for is an acute disturbance of cerebral function. It's possible while experiencing delirium, for instance, that you might not remember who a significant other is. But dementia is more prolonged, and delirium typically is an acute problem that disappears shortly. It's also important to note that depression can actually mimic the initial phases of dementia, but typically people that experience

dementia will progress far beyond the symptoms that are seen in people with depression. Dementia can occur at any age, but it's typically more common in the elderly. Statistics, of course, are hard to get exactly because it has to do with how many people we test and sample, but the prevalence of dementia in people between 50 and 70 years of age is about 1%, but those approaching 90, it reaches about 50%. In terms of the words we're using here, it's important to sort of get the language right, if you will. Mild cognitive impairment is a fairly recent term and it's basically used to describe people who have some problems with their memory but don't actually have dementia. In other words,

it's a potential precursor to dementia. Most people that get mild cognitive impairment are thought to be in the early stages of dementia, but the exact numbers aren't known that well. Some people will get MCI just due to life experience and stress, and it won't progress any further. Typically, in terms of risk factors for who gets dementia, age is a common one. In fact, it is the most common one. As your age increases, it increases your chance of getting dementia. If you have people with dementia in your family, the statistical chances of you getting dementia are higher. A lot of recent research has shown that incidents of head injury can play a role in the risk

factor for dementia. And finally, another one I'll mention here is fewer years of education. There's a lot of research that shows that the higher the level of education you have, the less likely statistically you are to experience dementia. In terms of the symptoms of dementia, we mentioned a few. Typically, you see reductions in memory. So you have trouble recalling date, names, and faces. You repeat questions and conversations. People get lost or they lose things. In terms of perception, people have trouble with sensory perceptions. They might have difficulty recognizing objects or other items in the world. Changes in executive function, the higher level brain systems,

so difficulties with initiating a task for instance. People with dementia typically get stuck and repeat the same action over and over again and possibly not considering the consequences of an action. And changes in language are quite common to see. Difficulty understanding words or complex sentences, difficulty finding the right word to use, and a reduced vocabulary. Now, there's many, many types of dementia, and this is when we'll add in the other word, because a lot of people think of Alzheimer's disease as dementia, and dementia is Alzheimer's disease. The reality is Alzheimer's disease accounts for 60% of the cases of dementia, but there are other forms. There's vascular dementia, Lewy body dementia,

frontotemporal dementia, just to name a few. In fact, there is a very long list of the forms of dementia, which I won't go through all of them here, but they're easy enough to find using various resources on the internet. Now, because Alzheimer's disease is the most common form of dementia, that's what I'll focus on here. Alzheimer's disease rarely occurs under the age of 45. Incidence increases with age. The cause is not known for sure, but we'll discuss some theories in a bit. About 30% of the cases are familial in the sense that there is a family history. As with the general symptoms I mentioned for dementia, these are the symptoms of Alzheimer's disease. Memory loss from recent events

progresses into dementia, total memory loss, inability to converse, loss of language. People typically with Alzheimer's disease have emotional disturbances or personality disturbances. Typically and sadly, they end up dying from opportunistic infections. In terms of the progress of Alzheimer's disease, typically the cognitive systems come on in the early stage. And when you're in the mild to moderate stage, that's when you begin to see the behavioral problems that are typical with this, so the emotional disturbances, for instance, and then death, typically three to nine years after diagnosis.

But of course, there's a lot of individual variability when you talk about these kinds of numbers. So we talked about some of the general symptoms of dementia, but what I'll do now is walk you through the three sort of classic stages of Alzheimer's disease. In the mild stage, this is where you see memory loss, language problems, mood swings, personality changes, and diminished judgment. As Alzheimer's disease becomes more moderate, you've got these personality and behavioral changes are emphasized, trouble with learning, long-term memories affected. You get instances of wandering, agitation, aggression, and confusion. And typically, people in the moderate stage require assistance. And in the severe stages,

people have a lot of problems with gait and other motor actions. They're bedridden. They're basically unable to perform normal daily tasks. And typically, this ends with placement in long-term care. The actual diagnosis of dementia and Alzheimer's disease is quite hard. Typically, CT scans can play a role in this and excluding massive lesions or other things that might be causing this sort of change in personality and behavior. Typically, on an MRI scan, you see atrophy commonly in the temporal lobe, but also in other brain regions. This is one way in which dementia and Alzheimer's can be diagnosed via neuroimaging. In fact, if this wasn't an audio podcast, you can clearly see the difference in a healthy brain versus an Alzheimer's brain if you look at a post-mortem examination of the tissue or an fMRI scan.

Typically, if you look at a slice of neural tissue from someone with Alzheimer's disease or dementia, you see an increase in neurofibrillary tangles, which are basically an abnormal accumulation of the tau protein. And of course, any kind of accumulation within a neuronal cell disrupts function. And the other thing that you see is what's called an amyloid plaque. Amyloid is basically a general term for protein fragments that have snapped off. They sort of accumulate in a little bundle. And again, this accumulation leads to disruption of brain function. So it's the buildup of amyloid plaques and neurofibrillary tangles that play a role in the reduction in brain function that you see in people experiencing

dementia or Alzheimer's disease. But what causes this to happen? So what causes the buildup of amyloid plaques or neurofibrillary tangles? Well, a lot of this has been related to genetic mutation now. Type 1 Alzheimer's disease basically are tied to several mutations in the APP gene on chromosome 21. Type 2 Alzheimer's disease is tied to issues with chromosome number 19. In type 3 Alzheimer's disease, there's a large number of mutations in the precentilin 1 gene on chromosome 14. And in type 4 Alzheimer's disease, there's typically mutations in the precentilin 2 gene on chromosome 1. But it's important to realize this is just a small picture. The array of

differences and the array of different types of Alzheimer's disease is constantly being speculated. But what these theories all have in common is mutations to the chromosomes result in the overproduction, for instance, of amyloid, which then results in those amyloid plaques, or they result in overproduction of tau proteins, which then create the neurofibrillary tangles. I'll finish by saying there is a debate here. While it's pretty clear that genetic mutations underlie Alzheimer's disease, there's still some debate as to whether it is the amyloid plaques or the tau proteins or a combination of both that leads to Alzheimer's disease and dementia. Thanks for listening today about the underlying mechanisms of dementia and Alzheimer's disease.

the underlying mechanisms of dementia and Alzheimer's disease. My name is Olaf Kregolson and I'm that neuroscience guy. You can learn more on www.olavkregolson.com or you can follow me on Twitter at that neuroscience guy. Thanks for listening and I'll see you on the next episode.