Читать книгу You: Staying Young: Make Your RealAge Younger and Live Up to 35% Longer - Michael Roizen F. - Страница 18

Before we crack some skulls and dive inside the brain, let’s quickly look at what memory really is: essentially, it’s the process of learning information, storing it and then having the ability to recall it when you need it – whether to solve problems, tell stories or save yourself on the witness stand.

Learning begins with those power connections in your brain: neurons firing messages to one another. Your ability to process information is determined by the junctions between those neurons, called the synapses. The ability of brain cells to speak to one another is strengthened or weakened as you use them. We’ll spare you all the biological miracles that take place between your ears, but essentially, the more you use those synapses, the stronger they get and the more they proliferate. That’s why you may have strong neural pathways for your family history or weak ones for 1980s music trivia. That also gives you a little insight into how you remember things. If something’s exciting to you, then you learn it faster – and train those synapses to make strong connections. But if the information seems more boring than the sexual habits of an earthworm, you can still learn and build those connections with repeated use.

FACTOID

Type 2 diabetes (the kind associated with being overweight) increases the risk of Alzheimer’s, probably by increasing inflammation or arterial ageing, but also because too much of the hormone insulin in the brain can stimulate beta-amyloid buildup. In fact, Alzheimer’s is now being called type 3 diabetes.

Problems arise when synapses lie dormant: the less you use certain connections, the greater chance they have of falling into disrepair (like losing fluency in a foreign language if you don’t use it for a long time). Technically, we actually learn by weakening underutilized synapses and repairing and strengthening the synapses we commonly use. So if you cook a lot and enjoy it, you’ll eventually know the recipes by heart – and learn them faster because it’s enjoyable. You build a large connecting wire, which allows for the faster flow of information. By contrast, lesser-used pathways fall into disrepair, so you lose or disable those connections. If you haven’t exercised your 1970s TV trivia synapse in a long time, then you’re not going to remember the name of the kid who played Bobby Brady on The Brady Bunch (ten points if you said Mike Lookinland before we did).

To keep your memory functioning at optimal power, you’ll need to focus on three aspects of your biology.

Your Brain. Let’s peel back your scalp and look through a peephole in your head. From the toupee’s-eye view, you can see that your brain has 100 billion nerve cells, and each cell receives one hundred messages per second. Yup. In the time it takes you to read this sentence, your brain cells have been doing more processing than the Inland Revenue’s computer server.

Your neurons – the cells that transmit information – look like mops with shaggy strings that reach out to one another, while the handles of the mops act like cables that carry the information. These neurons talk with one another with the frequency of eleven-year-old girls at a sleepover party; a lot of information is exchanged very quickly.

The hippocampus, which is shaped a little like a seahorse and is buried deep inside your brain (see Figure 1.1), is the main driver of memory. (The other two memory-related areas of the brain are the prefrontal cortex, which controls the executive function of your brain, and the cerebellum, which controls balance.) Your hippocampus processes information before it is stored. It works best when you’re either emotionally interested in the material or alert when you’re learning about it. That’s one reason why coffee may aid memory; it seems to increase your alertness the first time you learn something, which increases the chance you’ll deposit it in your long-term memory bank.

But for the purposes of ageing, we’re mostly concerned about what happens to the power lines within your brain. So flip on your hippocampus (or grab a cup of coffee) and remember this: there are protein fragments in your brain that sound like the name of a Star Wars droid – beta-amyloid – and they’re responsible for gunking up your power lines like overgrown vegetation or fallen branches. They’re probably responsible for causing Alzheimer’s. The primary defect in Alzheimer’s affects the input and output power lines of the hippocampus. Memory starts to fade. (The other physiological sign of Alzheimer’s is the buildup of what are called neurofibrillary tangles. They’re insoluble twisted fibres that build up inside neurons, like power lines getting crossed up and sending energy to the wrong location. These tangles influence intelligence.) Now, a downed branch here and there won’t do much to disrupt the flow of energy through your entire city, but what happens when a lot of branches or shrubs or trees fall on the same part of the grid? You’re out of commission.

Figure 1.1 Storage Units Memories are stored in the hippocampus. The other two major memory-related areas of the brain are the prefrontal cortex (controlling the executive function of your brain) and the cerebellum (used for balance). Craving memories are found in the insula.

In general, genes control how much beta-amyloid you have. Some branches may be knocking out those notes from your course in eighteenth-century Roman history, while others may be causing you to forget to pick up the very thing that you went to the supermarket for in the first place. But your genes don’t have complete control. You can alter the amount of gunk you have weighing down your power lines by altering the expression of one of your genes: the Apo E gene, to be exact. Apo E protein acts like the power company crew that removes the branches and sap from the power lines after the storm. It sweeps through and removes the beta-amyloid so that your synapses can keep functioning and you don’t lose the ability to remember what year Diane Keaton won an Oscar for best actress (1977). Whenever we create new synapses to help our brain improve itself, some of this beta-amyloid remains behind, and the Apo E workers clear the gunk to ensure a clean connection.

One group in the union, however, local Apo E4, sabotages the effort to restore power and even gunks up the power lines further (see Figure 1.2). Research shows that an elevated level of the E4 protein is correlated with a higher incidence of Alzheimer’s. Fortunately, there are things you can do to turn down the activity of the E4 gene and allow the rest of the Apo E team to clear your power lines. Eating turmeric, which is found in Indian foods, seems to reduce expression of the E4 gene (India, by the way, has a relatively low incidence of Alzheimer’s). Exercise has a similar effect.

Your Blood Supply: While there’s a strong genetic component to memory problems, we’d be remiss if we didn’t address the arterial component of an ageing brain. A lack of healthy blood flow to the brain is one of the other main causes of forgetfulness. Each side of the brain has a separate blood supply that looks like several large trees during winter. Between the twigs at the tips of the major branches are areas of brain that are dependent on blood from each of the surrounding trees. The area farthest from two blood-supply lines is the watershed area where we tend to have ministrokes when the branches of surrounding trees are pruned by atherosclerosis or the tree trunks themselves wither from poor maintenance (see Figure 1.3). Cholesterol-lowering statin drugs may help maintain memory by preserving tree architecture, while also reducing inflammation that ages the brain cells directly (more on arterial health in the next chapter).

Figure 1.2 Power Outage Apo E proteins that bind cholesterol are like workers clearing junk to ensure a good connection between neurons. Apo E4 gets in the way, and the power lines sag under a substance called beta-amyloid.

Figure 1.3 Delivery Failed When blood (and the nutrients it’s carrying) can’t get to the brain, tissues shrink – and you start to lose memories.