How does aging affect your brain?
You think you are so smart, capable, rational, and full of the same magnificent power that invented pizza. But as soon as you settle into that idea, you’ll need to turn your house upside down looking for the spectacles you were already wearing the whole time.
No need to worry. It’s just a sign of aging and it happens to everyone who’s got a brain in their skull.
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Your brain is an amazing, complex organ. It’s active all the time, even when you’re asleep. It works in the background controlling your digestion, body temperature, breathing, heartbeat, hormone balance, and metabolism. Of course, it also lets you move about by using your muscles.
Unfortunately, just like every other part of your body, your brain only functions optimally when you’re young, slowly declining as you age.
How Does Aging Affect Your Brain?
There are some definite, measurable changes that occur in the physical structure of your brain as you age, which ultimately lead to changes in its function. These physical changes include:
- A decrease in brain size
- A reduced number of brain cells
- A loss of healthy, insulating fat
- A buildup of fatty deposits between brain cells
Interestingly, all of these changes actually stem, directly or indirectly, from one single consequence of aging that actually has nothing to do with your brain itself: poor blood flow. Of course, it’s your heart and blood vessels that are responsible for keeping blood flowing to your brain! But, when their functions begin failing (from atherosclerosis, heart disease or heart failure), your brain can begin to suffer as well.
How does a simple decrease in blood flow lead to such serious changes in the physical structure of your brain? How does the process of aging affect your brain? To understand how these processes work, it’s helpful here to take a step back and look at how normal blood flow to the brain works!
Healthy Brain Blood Flow
Like all the other organs in your body, your brain relies on oxygen and nutrients from your blood to stay active and healthy. But, getting those life-supporting molecules into your brain is a bit more complicated than for the rest of your body.
See, your brain is actually physically separated from your blood by a special layer of cells called the blood-brain barrier (BBB). The BBB is there to protect your brain from infection and toxins that might slip past your immune defenses and into your body. It’s an extra layer of protection — like a lock on a bedroom door inside a house — to help make sure that, no matter how bad off the rest of your body might be, your brain can do its super important jobs!
The BBB filters your blood for you, into something called your cerebrospinal fluid (CSF). CSF is a liquid that absorbs all the goodness from your blood and it’s what actually bathes your brain in nutrients (oxygen, sugar, amino acids and electrolytes) so that it can function well.
The CSF is also responsible for transporting waste products from your brain (carbon dioxide, urea, etc.) to the BBB, where they can cross back to the blood and be transported out of your body.
Aging, Decreased Blood Flow and Brain Health
As you can see, getting nutrients into your brain is quite complicated! And you might think, “Well, your blood itself isn’t responsible for directly feeding your brain… so… CSF is more important for keeping your brain healthy! Blood is less important for the brain than other parts of the body.” But actually, the exact opposite is true.
That extra step of everything — nutrients and waste products — having to filter through the BBB to get into and out of your brain, makes really good blood flow more important in your brain. The BBB slows down nutrient exchange. So, if you slow down how quickly nutrients make it to the BBB (via slower blood flow), it’s more likely that the rate nutrients and waste make it to/out of your brain cells will drop too low. If this happens, the particles that enter and exit your brain become unbalanced, and this can have serious consequences for the health of your brain.
Unbalanced ratios of molecules in your CSF can lead to something called “oxidative damage” or “oxidative stress”. Just like injuries to the outside of your body (scratches, scrapes, etc.), the “injury” caused by oxidative damage in your brain activates your immune system. Just like it’s supposed to, your activated immune system then starts making chemicals to help heal your body. Unfortunately, when the injury is caused by something like poor blood flow (and can’t be really “healed”), these chemicals can build up in the brain and stick around for too long.
This is referred to as a state of “chronic inflammation” which, ironically, ends up damaging your brain more.
This mixture of damage from oxidative stress and chronic inflammation leads to a breakdown of important structures in the brain: brain proteins, protective fats and brain cells. As these proteins, fats and cells breakdown, they stop working and, ultimately, die. This causes all the changes in brain size, structure and function associated with aging.
Aging Brain Structures and Brain Signals
Aging affect your brain through changes in your brain’s structure. The first consequence of changes in brain size and structure as you age is a decreased ability for your brain to send signals between nerve cells. There are several reasons for this.
First, the death of brain cells and a general shrinkage of the brain (5% per decade, starting around age 40), simply gives your brain fewer tools to work with. Fewer brain cells means fewer brain signals can be sent over a given time period.
Second, the breakdown of protective fat makes it harder for the remaining brain cells to carry signals normally. This protective fat, called myelin, is normally wrapped around the outside of your brain cells and works very much like the coating of a power cable. It creates a layer of insulation so that messages sent as electrical impulses can get from their origin to their destination. Without it, brain cells struggle to carry an electrical signal from one end of their bodies to the other.
Third, in an attempt to protect the overall 3D-structure of your brain, your body fills up the spaces that used to have brain cells in them with little fatty or fluid deposits. While myelin fat around the outside of your nerves is good, fat between your nerves is a problem. Fat, after all, stops brain signals from traveling. If fat builds up between two nerves, the signals that do make it to the end of a nerve struggle to make it across the gap to the next one.
Together, these three effects can lead to some serious decreases in brain signaling. Now, you can’t feel changes in brain signals themselves, but you do notice the consequences of fewer brain signals: changes in your cognition.
What Changes in Cognition Occur with Aging?
Typically, the part of your brain most often affected by structural changes is the part you need for learning new information, thinking critically, making decisions and storing short-term memories. So, these are the brain functions that usually dull as you age.
Practically, this means you notice changes in how often you forget things. You’ll suddenly can’t remember what was on your grocery list, or that you needed to pick up your prescriptions, or the name of your neighbor’s new baby.
This can be pretty frustrating, especially since your long-term memories, which are stored in a different part of the brain, are usually just as fresh and clear as when you first made them. So, you feel like your memory is working great, but you can’t remember anything new!
You may also notice that, though you can still learn new things, it takes you a little longer. This is in part due to the memory glitches (how can you learn a new language if you forget all the words?) but also because your ability to process new information also slows down. You may need to have people repeat things for you because you can’t process all the information you’re hearing at the speed you’re hearing it. Hear things a second or third time lets you pick up details you missed the first time around.
A Healthy Brain Aging vs An Unhealthy Aging Brain
All of the processes we’ve talked about up to here are “normal” or “healthy” brain aging. Researchers think these processes occur in everyone’s brain as they age. In most cases, the effects are generally mild or moderate (though, nevertheless annoying).
In some cases, though, these processes spiral out of control and lead to “unhealthy” brain aging or diseases. There are a few brain diseases that can develop from unhealthy brain aging, depending on exactly which processes are most out of control.
Alzheimer’s disease is the most common neurodegenerative condition in the United States. It is thought to be caused by excessive build-up of waste products in your brain. Specifically, researchers think the build-up of small protein fragments in the brain lead to the symptoms of Alzheimer’s.
At first, these small protein fragments cause symptoms by getting in the way of brain signals between brain cells. As they build-up further, though, these fragments can become toxic to brain cells and kill them. This speeds up total brain shrinkage and causes severe cognitive decline.
Parkinson’s Disease is the second most common neurodegenerative condition in the United States. This condition may come from uneven rates of death between types of brain cells during aging. In Parkinson’s disease, brain cells that make the essential chemical, dopamine, die at a faster rate.
Your brain uses dopamine to send messages between brain and nerve cells. When too many of the cells that make dopamine die, your brain can’t make enough dopamine anymore. This lack of dopamine causes the brain to be unable to send messages properly. And without proper nerve messaging, you can start to see cognitive declines and physical symptoms of Parkinson’s disease.
Depression is another common sign of unhealthy brain aging. This neurocognitive condition is thought to be caused by a general reduction in total brain function from a lack of healthy nutrients and a poorly balanced CSF. Without proper nutrients, the brain cannot make all the normal hormones and chemicals that it needs to regulate your mood, leading to the symptoms of depression.
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Take Home Message
Aging affect your brain in many ways. Changes in blood flow to your brain as you age drive multiple physical changes to the structure of your brain. In most people’s brains, these physical changes make your brain cells a little less efficient at communicating with one another. This results in a slight decrease in the ability to process new information and make new memories. In some people’s brains, however, these changes spiral out of control, leading to serious neurocognitive conditions, like Alzheimer’s, Parkinson’s and depression.