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Contents

What is memory?

Short-term memory

Long-term memory

How we remember

As good as memories in the bank

Stage one: Acquisition

Stage two: Consolidation

Stage three: Retrieval

Forgetting: What’s normal?

Seven types of normal memory problems

How memory changes with age

Why memory fades

When brain cells die

Growing new brain cells

Changes in brain structure

Memory impairment: Normal aging or brain disease?

Mild cognitive impairment

Dementia

Health and lifestyle factors linked to memory problems

Obesity

Cardiovascular disease and its risk factors

Diabetes

Metabolic syndrome

Depression

Hearing loss

Hormones

Medications

10 ways of life to promote memory health

SPECIAL BONUS SECTION: Improving everyday memory

When to see a doctor

Medications for memory impairment

Resources

Glossary

Dear Reader,

Years ago, I saw a patient in the beginning stages of dementia. She still had moments of great clarity, and in one of those times she lamented, “I’m vanishing as a person.” Her words have stuck with me because they seemed like such a lucid description of the impact of dementia on a person.

In many ways, our memories shape who we are. They make up our internal biographies—the stories we tell ourselves about what we’ve done with our lives. Our memories tell us who we’re connected to, who we’ve touched during our lives, and who has touched us. In short, our memories are crucial to the essence of who we are as human beings.

Memory loss also affects the practical side of life. Remembering how to get from your house to the grocery store or how to do the tasks that make up your job allows you to take care of your needs. That’s what makes dementia so scary—losing your memory means both losing your ability to live independently and not being able to remember your past experiences. It’s not surprising, then, that concerns about cognitive decline rank among the top fears people have as they age.

And there’s no getting around the fact that the ability to remember does change with age. Many of these changes are normal, and not a sign of dementia. As you’ll read about in the section of this report titled “Forgetting: What’s normal?”, many of these changes increase as the brain ages. Unfortunately, some people have the more serious memory problems associated with dementia. We will review the different forms of dementia, too.

If your memory is still healthy—even if you’re forgetting a bit more than you’d like—now’s the time to commit to protecting your brain from ill consequences. When it comes to the brain, one key to successful aging is what experts call cognitive reserve, the brain’s capacity to withstand damage associated with disease or injury. Although scientists once thought that the adult brain did not grow new brain cells (neurons), we now know that the brain keeps making new cells and connections throughout life. This plasticity, or ability to change, means that you may be able to have an impact on neuronal growth. This report discusses some new research on this subject and gives examples of memory strategies that may help.

Though the connection may not seem obvious at first, keeping the rest of your body healthy is a crucial way to preserve your memory. Many medical conditions—from heart disease to depression—can affect your memory. Staying physically and mentally active turns out to be among the best prescriptions for maintaining a healthy brain and a resilient memory.

Sincerely,

Kirk R. Daffner, M.D.
Medical Editor

What is memory?

Memory is often used as a catchall phrase referring to a person’s general thinking (cognitive) abilities. Actually, memory is just one—albeit very important—aspect of cognition. It refers specifically to all that you remember as well as your capacity for remembering. Not all memories are created equal. Some memories are meant to be retained for a short period and then discarded. For example, you remember the telephone number of the local pizza place only long enough to make the call. But memories that are more important are stored in the brain and can be retrieved at will: the names of close friends and relatives, the multiplication tables, your phone number, and other information you use regularly. Certain kinds of information can be memorized only if you concentrate, whereas other kinds of memories, such as the faces of people you see regularly and the steps of simple everyday routines like brushing your teeth, are absorbed without conscious effort. The process of learning new information, storing it, and recalling it involves a complex interplay of brain functions (see Figure 1).

Deep within the brain, a structure known as the hippocampus plays a crucial role in acquiring and consolidating new memories. The nearby amygdala is the part of the brain that reacts to emotionally powerful information, helping the brain retain information that has emotional impact. Once a memory is established (consolidated), it is stored mainly in areas of the cerebral cortex, the large, domed outer layer of the brain.

Researchers and neuroscientists have devised several classification systems to describe the various forms of memory. One major system relies on duration, making a distinction between short-term memories, which are fleeting, and long-term memories, which can persist for a lifetime. Another scheme breaks memories down according to the type of information they contain, such as whether they are straight facts, specific events, or learned procedures for doing something.

Forming and storing a memory is a multistep process that involves several parts of the brain. The memory of an event is not a single entity, like a book on a shelf. Instead, it is the aggregation of multiple streams of sensory information, filtered through the perception of the person observing or participating in the event. Each of the different components of a memory is stored and processed in a different region of the brain. It is not uncommon for a person to have problems with one type of memory, such as recalling specific events, but to function normally in other areas, such as remembering routes to different locations.

Short-term memory

This is information that the mind stores temporarily, encompassing what you need to remember in the next few seconds or minutes. Short-term memories include, for example, the name of the person who just spoke at a dinner party (as well as what that person said), and the date and time of the appointment you just made—and must remember only until you write it in your date book.

Working memory is a form of short-term memory that involves actively holding information and manipulating it. For example, working memory comes into play when you remember prices at the supermarket while at the same time performing a computation with them so you can compare costs between different brands or quantities.

Short-term memories are supposed to be fleeting. They turn over at a high rate because new ones are continually replacing them, and there are only so many short-term memories you can keep in mind. Research shows that the average person can hold only about seven (plus or minus two) unrelated “bits” of information in mind at one time. That’s why it’s easier to remember a seven-digit phone number than a longer number such as the identification number on a driver’s license.

The relatively transient nature of your short-term memory is actually beneficial because it allows you to discard unnecessary information. Imagine what life would be like if you kept every short-term memory—the name of the telemarketer who called your house an hour ago, the price of each dish you ordered from a Chinese restaurant, what color tie your friend wore yesterday. Your mind would be so overloaded with trivia that you’d have trouble focusing on the things that really are important. It would be as if you kept all your junk mail and let it bury your personal letters, bank statements, and other important documents.

Short-term memory has another limitation. It’s fragile and easily disturbed by interruptions. If you’re trying to remember a phone number and someone walks into the room and asks you a question, chances are you’ll forget the number and have to look it up again. That additional bit of information (the question) “bumps” the short-term memory out of your awareness.

Long-term memory

Although most unimportant short-term memories quickly decay, the brain stores the important ones—those that are emotionally compelling or personally meaningful. That stored information is long-term memory. It is the total of what you know: a compendium of data ranging from your name, address, and phone number and the names of friends and relatives to more complex information, such as the sounds and images of important events that happened decades ago. It also includes the routine information you use every day, like how to make coffee, operate your computer, and carry out all of the intricate behavioral sequences involved in performing your job or running your household.

Your long-term memory and short-term memory are not distinguished merely by how long the memories last. Another difference is the amount of information each memory system and its associated brain regions can handle. Although the brain can juggle only a relatively small number of short-term memories at a time, it can store an enormous number of long-term memories. Barring disease or injury, you can always learn and retain something new. Furthermore, long-term memories are less fragile than short-term memories, which means they’re not lost when something interrupts your train of thought. Some types of previously learned long-term memories even tend to remain intact in the early stages of dementia, when patients have trouble learning new information (see “Dementia,”).

Maintaining a long-term memory often requires that you periodically “revisit” it. Some long-term memories that go unused or become irrelevant fade or become distorted over time. Have you ever read a book that you loved, but years later found yourself unable to recall much more than the title? That’s probably because you hadn’t thought of the plot and characters in a long time. On the other hand, some long-term memories are amazingly persistent, no matter how infrequently you use them. For example, many adults are surprised by their ability to remember minute details of their youth—an unjustified punishment they received, a fifth-grade science project, their first date. Interestingly, research demonstrates that although long-term memory is more durable than short-term memory, it is also changeable. For example, the way you remember your first romance can evolve over time in response to experiences and information you acquire years later.

Long-term memory can be divided into two categories: declarative memory and implicit memory. (We will discuss one form of implicit memory, called procedural memory).

Declarative memory

Also known as explicit memory, declarative memory is information that requires a conscious effort to recall. There are two types of declarative memory: semantic memory and episodic memory. Semantic memory is factual knowledge, such as the names of the continents, the color of your spouse’s eyes, or what winter is. Much of the basic information you acquired during your school days falls into this category. In addition to being factual, semantic memory has another key characteristic: it is not bound to a specific point in time. You can’t point to the exact moment when you learned that George Washington led the Revolutionary War, for example. And even if you can remember the specific day when you learned the multiplication tables or other facts in school, the timing isn’t important to your knowledge of them.

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