That Neuroscience Guy - The Neuroscience of the Aging Brain

Episode Date: June 11, 2022

In the last episode, we discussed how the brain changes as we grow from babies to young adults. But what about the other side of the spectrum; what happens to our brain as we age? In today's episode of That Neuroscience Guy, we discuss the neuroscience of the aging brain. 

Hi, my name is Olaf 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. Now, a couple of administrative things first. Sorry for the gap in release. I had to take some personal time. I just wasn't able to record episodes. But we're going to get caught up and get back to track.

So today I'm going to record an episode that would have been playing last Sunday. And I'm going to record a bite. And then tomorrow I'll record Sunday's episode and we'll be back on track. The second is a correction. During the episode on boredom, maybe I was bored. No, I'd never be bored making a podcast, but I stated there were between 4 and 6 million neurons in the brain. That's completely not true.

The current best estimate is about 86 billion neurons in the brain. So sorry for that little gaffe, and thank you for the correction that was emailed to me because we missed that when we were editing the show. Okay, to get us going here, the last time we did a full episode, we talked about the growing brain. So how does the brain grow? And with a bit of a focus on the teenage brain. Today, I'm going to deal with the aging brain. Now we all get older. There's nothing we can do to avoid that. And not to be down, but we're all going to die eventually. But what goes on in the brain as we age? So where we got to on the last episode is I

basically walked you through how the brain grows and how you basically get to your early 20s. And as that's happening, there's a lot of changes that occur. So for instance, one of the things we talked about was the fact that when the brain is born, there's not as many neurons and there's not as many connections. But very rapidly, the brain is full of neurons with tons of connections. And then pruning occurs where the brain is basically trimming itself down so only the connections that are needed are there. And like I just said, by the time you get into your late teens or earlier in some cases, your prefrontal cortex is coming online, which is sort of the last thing to finish off,

and the brain is healthy and ready to go on with life. Now, it's important to realize that neuroplasticity doesn't stop there. There is a lot of evidence that shows that adults can still have neuroplasticity doesn't stop there. There is a lot of evidence that shows that adults can still have neuroplasticity. And even now, recently, it's been suggested that new neurons can form. Now, previously, this was sort of an idea that wasn't supported. The idea was that once your brain got to sort of your early 20s, the number of neurons you had was constant. But now there's evidence that at least in some parts of the brain, there are neurons forming throughout your life.

Now, of course, the other important thing to realize is there's always formation of new connections. So even right into your end of life years, you can learn new skills. And the reason you can is because while the total number of neurons stays relatively constant, except for those few exceptions I mentioned, what's happening is you have new neural connections forming. So, what about death? Well, like I said at the outset, we know that everyone's going to die, but the truth is relatively few people die of old age. That's a bit of a myth. Most people die from other issues. So heart and circulatory disorders, cancer, respiratory disorders, nervous system disorders, digestive disorders, kidney disorders, and the list goes on and on. So very rarely is the cause of death old age.

So what's happening in the body and what's happening in the brain? And I'm going to tackle a bit about the body to set the stage for the brain. The sort of classic definition of what biological aging is, is a decline and deterioration of functional capability at the cellular, tissue, organ, and systems level. Now, what does that actually mean? It basically means your body's ability to do things is reduced. One of the big ones that happens is your body loses its ability to maintain homeostasis. And this is tied to your nervous system. Homeostasis is your body's ability to say to regulate temperature amongst other things. And with degeneration of the nervous system, your body loses your ability to

do this, or at least you're less efficient in maintaining homeostasis. And as a result, you're more susceptible to things like injury or illness. Your body also has a decreased ability to adapt to internal and external stress. Basically, your body, as it wears down, isn't able to handle all of the things that life throws at us. And a good example is if a young child breaks their leg, they get up and going pretty quickly. But if you're in your 70s or 80s and you break your leg, it could be a life-threatening injury. And finally, the other piece of normal biological aging is damage to body systems. There is just wear and tear across the lifespan, and those systems never heal 100%. And because of these three changes, the loss of the ability to maintain homeostasis, And because of these three changes, the loss of the ability to maintain homeostasis,

decreased ability to adapt to internal and external stress, and damage to body systems, basically what happens is you're more vulnerable to disease and mortality. So those causes I mentioned briefly, they're more likely to occur because your body's wearing down. Now, why do we age? There's sort of two big theories that are out there, and they are still debated, because the truth is, I would say at this point in time, there is no consensus among scientists. There are definitely scientists that have opinions about why we age, but not everyone's in agreement. And the two big theories about why we age are what are called error theories or programmed theories. Error theories are related to wear and tear, for instance, which is your body, due to mistakes, just takes on aging.

Rate of living. Basically, people have proposed that cells have a lifespan, if you will, and they can burn out. Cells have a lifespan, if you will, and they can burn out. There are cross-linking theories, so that cross-linked proteins can damage organs. There are free radical theories. These are atoms with unpaired electrons, and they do damage to what they encounter. They basically just fly around through the body and the brain and break things up. And there are theories about DNA damage. So all of the error theories basically say that something's gone wrong and that's why we age. Programmed theories are quite different. Programmed longevity,

which is one of three prominent programmed theories, is basically that aging is in the genetic code. Our body begins to turn itself off and we age. There is the endocrine theory, which is basically stating that it's in our hormones. So changes in our hormones result in aging. Then there's the immunological theory, which is basically our immune system is programmed to shut down. And as a result, we're more susceptible to things that might cause us to die. But like I said, the simple truth is scientists are still not sure why we age. Now, what's happening specifically in the nervous system? I've hinted at some things,

but let's really dive into the nervous system. Basically, your brain grows, like we said, in the early stages. And at the adult, you have what's called a healthy brain, and everything's supposed to be there. But as we age, the brain itself changes. And the primary reason for that is neural degeneration. From the time you're in your early 20s, you're typically losing about 10,000 neurons per day. So what that means is these neurons are basically gone. Now they could be because of programmed reasons or because of error reasons, but you're still losing them. And they're not replaced. So basically your nervous tissue is gradually reduced. Now if this was a video podcast, I could show you some really cool images of this, but all you have to do is go to Google Images and put in the aging brain. In a young, healthy brain, if you look at an MRI scan,

you'll see that the folds of the brain are very tight. There's not a lot of gaps and the brain is pushed together. And with the aging brain, it opens up. You see gaps in the folds of the brain, the sulci and the gyri, and you see these gaps appearing, and this is because of this loss of neural tissue. And as a result of losing this neural tissue, your brain is just not as effective as it once was. And if you looked at an Alzheimer's brain or a person with dementia, what you would see is that those folds are even more open, which is one of the reasons that people with Alzheimer's or dementia have the deficits that they have. Now, again, theories on neuronal death have changed a lot over the past decade. We know what's going on, but now it's believed that most neuronal death is due to non-age-related factors, so damage from external causes or neurodegenerative disease.

Now, there is some evidence that there might be a loss of myelin as we age. And myelin is basically the fatty sheath that covers neurons to help them transmit information. And if you lose myelin, then you will have a reduction in neural function. So if you combine that with things just breaking because of error-related factors, you have a loss of brain function. And because of a loss of neurons and a loss of myelin, that gives you overall decreased brain mass, which as I said, leads to loss of function. And one thing to note is that this loss of brain mass isn't uniform across the brain. For reasons that we're still trying to figure out, some parts of the brain are harder hit than others.

So in other words, some parts of your brain stay active, and other parts of your brain basically aren't functioning nearly as well as they used to. Now, let's assume your brain is healthy and tackle a few things before I wrap it up. There's a couple of myths about aging. Memory declines drastically with age for all people. That's not 100% true. IQ declines drastically with age in all people. Again, not true. Learning becomes more difficult as we get older. Again, not true. Learning becomes more difficult as we get older. Again, not true. And the last one's probably the most important one. There is nothing you can do to counter these aging deficits. So some things do change. Sensory information and our ability to process sensory information is reduced with aging.

But in terms of cognitive function, basically verbal scores are stable with age. So people that go well into their 70s and 80s still have pretty good verbal memory. However, nonverbal scores decline with age. So this would be like manipulating shapes or doing tasks that are not verbal in nature. Now even within that, it depends on the kind of verbal memory we talk about. So people as they get older maintain their ability to recognize words and it's pretty stable. But the number of words, the total number of words that they can recall declines with age so some parts of memory are impacted and not others the key thing i

want to the key point i really want to make is that the changes that occur in your brain with age are really due to the brain breaking in a sense and wear and tear, which I've mentioned a few times. And they don't have to occur. If you maintained a healthy brain and you never had a concussion and you did all the things you're supposed to do to maintain good brain health, statistically, your brain will remain healthier and you won't have the same level of decline as other people. And on the bite coming up, I'm going to mention just a few things that you can do to maintain good brain health in the face of aging. So I hope you learned a little bit about the neuroscience of aging and what happens with aging. Again, just an apology that we're a little late with this episode. This is entirely on me. Had to take some personal time. Again,

please remember the correction, 86 billion neurons in the brain that's the truth and i'm not sure why i misspoke myself and of course there's the other things you can do to help us out remember we got t-shirts on the etsy store um you can help us through patreon by uh donating money every month it goes to the graduate students in the krigolson lab uh please follow me on twitter at that neuro guy dm me questions ideas and to be fair, that fix that was suggested came in from direct messaging. And finally, of course, please subscribe and listen to the podcast. My name is Olaf Kregolsen, and I'm that neuroscience guy. Thank you so much for listening, and I'll see you on the next neuroscience bite.