That question came up during a recent conversation with a friend. It’s a common topic, since most of us will in some way be affected by Alzheimer’s disease during our lifetime.
“Alzheimer’s patients can recall what happened 50 years ago,” said John, “but they can’t remember what they had for lunch yesterday. How do you explain that? Does anyone have the answer?”
“I can tell you what I know about the subject from a lay person’s perspective,” said Peter. “Here’s the answer to your question: Because Alzheimer’s patients don’t have enough of the neurotransmitter acetylcholine (http://health.ccm.net/faq/2195-acetylcholine-definition) to learn and recall information, they can’t encode yesterday’s lunch correctly.”
“C’mon, Peter,” said John. “Your answer is probably correct, but the language is too difficult for most of us to understand. Can you explain it in plain English?”
“No problem,” Peter replied quickly. “Most people today use computers, so let me try to explain the Alzheimer patient’s problem by using a computer analogy: When you want to save your computer work—let’s say it’s an article—you click onto the save icon, and the computer program encodes (https://en.oxforddictionaries.com/definition/encode) your article so that you’ll be able to retrieve it whenever you want to.
If your computer didn’t save (encode) your article properly, however, you won’t be able to retrieve it at all. That’s how encoding, or saving something in the form of a code, works with computers.
Like computers, the human brain encodes each memory you want to retain. Whatever you want to remember, be it a person, place, thing, or event, it goes from your short-term memory to your long-term memory as encoded information.
The big question, ‘How does the brain encode memories?’ can be answered this way: To encode memories, the brain relies on a neurotransmitter called acetylcholine. To encode and recall memories, the brain needs acetylcholine. Unfortunately, as a person ages, the amount of acetylcholine in the brain decreases. Alzheimer’s patients suffering with severe memory loss also experience a severe loss of acetylcholine. In other words, to properly remember at any age, you need a sufficient level of acetylcholine to encode and to retrieve your memories.
Now we’re coming to the conclusion: You’ll be able to remember an event even 50 years after it occurs, but only if you had a sufficient amount of acetylcholine at the time of the event.
Consider Alzheimer’s patients. They’re able to remember childhood events because, when they occurred, these individuals had normal levels of acetylcholine. This is why their brains are able to encode their childhood memories correctly.
However, an Alzheimer’s patient cannot correctly encode yesterday’s events, because at the time of those events (yesterday), he or she no longer had enough acetylcholine to properly encode what occurred. And when the brain can’t encode information, it has trouble retrieving it.”
“Are you saying, Peter, that not enough acetylcholine in the brain is what causes Alzheimer’s disease?” asked John.
“No, I’m not saying that at all. The cause of Alzheimer’s is more complicated than the loss of acetylcholine. In fact, we still don’t know the real cause of the disease or, unfortunately, how to cure it.
Hopefully, in the near future we’ll be able to cure Alzheimer’s disease. Although there is still no consensus on the best way to prevent Alzheimer’s, it’s known that maintaining a healthy lifestyle improves one’s overall health.