S2E9. The Aging Brain: Part I

Last week’s episode touched on the idea that to really understand dementia, you first have to understand the dynamics of normal aging and how it affects brain function. This made a lot of sense to me and whet my appetite to learn more. So I googled around and found an on-line course titled “The Aging Brain.” 

I bought it and started watching it this week. There are 12 lectures of about half an hour each. I thought I’d pass along some of the highlights from the first 4:

1. As we age, the speed with which we process new information slows down. We also experience drop-offs in executive function and episodic memory. On the other hand, we actually perform better on tasks of ‘crystalized intelligence’ which is knowledge of facts and information, like vocabulary. Perhaps not so surprisingly, up to about our late 70s, we oldsters actually outperform the young’uns on these measures!

2. About 25% of the effects of aging are controlled by our genes, so there is some degree of senescence built into our DNA. Bottom line: we will age and die. Conversely, 75% of aging’s effects are a function of our environment, so there should be a variety of ways for us to slow down the harmful effects of aging by managing our behaviors and lifestyle choices.

Fun fact: Lobsters rarely die of old age and can live for hundreds of years! (Click here to learn more.)

3. The effects of aging (motor slowing, sensory decline, physical changes, etc.) seem to be related to changes in 3 cellular processes involving energy consumption, free radicals and damage to our DNA.

Although there haven’t been long-term experiments with humans, it appears that restricting one’s caloric intake can add years to one’s lifespan. It’s hypothesized that in a time of food scarcity, our metabolism slows and our cells hunker down in a maintenance mode and focus on repairing themselves. With healthier cells, the effects of aging are slowed-down.

A second aging pathway is through the action of free radicals. Although these molecules that are missing an electron perform important functions, too many can set off a chain reaction that creates more and more free radicals and damages cells. This process is known as oxidative stress. The bad news is that taking anti-oxidant supplements doesn’t seem to help. The good news is that eating a diet high in antioxidants (e.g., fruits & vegetables) does have a significant impact in slowing down the aging process.

Thirdly, our DNA is constantly under attack from things like free radicals, ultra-violet rays and tobacco smoke. DNA strands are constantly being broken, other molecules attach themselves where they don’t belong, bends and kinks can form, and there can be errors in replication when cells divide. Fortunately, we have a system that works to repair this damage…but it isn’t able to fix everything. Over time, the DNA in enough cells becomes corrupted to have a significant impact, i.e., we age.

It is believed that the interaction of these three factors account for many of the ‘symptoms’ we associate with normal aging.

4. These processes affect brain cells, too, but there are some brain regions that are more susceptible to cellular deterioration and subsequent shrinkage over time. Most importantly, it’s the prefrontal cortex which controls executive functions and the hippocampus which is essential for memory that shrink the most as we get older.

The prefrontal cortex is responsible for, among other things, setting goals, creating, implementing and monitoring strategies, focusing attention, working memory and higher-order reasoning and thought. It can shrink by as much as 50% between our 20s and our 80s. It’s easy to see why we make more and more errors as these functions break down.

The typical shrinkage of the hippocampus between our 20s and 80s is about 30%. Unfortunately, we need our 2 hippocampi to function properly in order to form new memories of our experiences and to recall our past (episodic memory). With this loss of volume, that becomes harder and harder to do as we get older.

The other major contributor to cognitive problems as we age is the loss of the insulation around our brain cells’ axons (the long extensions from the cell body that connect neurons). This fatty coating is called the myelin sheath and its insulating properties can speed transmission between neurons from a leisurely walking pace to over 200mph. 

Over time, though, there are breakdowns in the coating and the transmission of electrical signals between neurons becomes less efficient. This is the cause of the well-documented slowing in processing speed as we age. As it turns out, though, weakening of the myelin sheath is also correlated with declines in executive functioning and episodic memory. It’s a double whammy.  😦  

Pretty depressing, eh? Not really! Keep in mind that this is what NORMAL aging looks like. The comparisons in this line of research are made against the age of our peak performance (20s-30s), so even with these drop-offs, we can still function pretty well…just not as fast or efficiently as we used to. Going forward, we’ll need to use the normally aged brain as the baseline against which to compare the deficits that come with dementia.  

There is good news ahead…I promise! But this is more than enough to chew on for one week.

To be continued…

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