What Is Memory

When we talk about memory, we mean not only all that we remember but also our capacity for remembering. You might think that an optimal memory is a huge database that faithfully records and securely stores all that you have learned and experienced in your life. But actually, that wouldn't be optimal at all.

Not all memories are created equal. Some are meant to be retained for just a short time and then discarded. Imagine if you carried in your head every phone number you ever dialed or the time and location of every movie you ever saw. These memories would clutter your mind and, like outdated clothing in the closet or junk accumulated in the garage, they would make it harder for you to find the things that you need.

Memories that are important or emotionally powerful are stored in the brain for the long haul. This information is so ingrained that it is a part of you—images, experiences, and knowledge that have become intrinsic aspects of your psychological and social identity. Your memory includes facts and images, like the names of close friends and the faces of loved ones. It also includes procedures and skills, like how to drive a car or swing a golf club, and the specialized knowledge that you use for your work. It's when we start to forget these important things that most of us begin to worry.

The process of learning new information, storing it, and then retrieving it involves a complex interplay of brain functions. Understanding this process can help you appreciate why some memories endure and others fade away. Different parts of the brain play a role in whether you remember something over the short term or the long term.

Short-Term Memory

Short-term memory is information that you need to remember for just a few seconds or minutes. After that, it vanishes. It's the date and time of an appointment you just made—and must remember until you write it down in your calendar or personal digital assistant (PDA). Working memory is a form of short-term memory that's a bit more complex. Working memory comprises information that you hold in mind for a brief time to use for some specific purpose. Think of working memory in terms of your computer—as information that you need to keep up and running in an attentional window.

Working memory comes into play, for example, when you have to consider certain options and then make a decision fairly quickly. Let's say you're in the supermarket and you're trying to decide whether it's more economical to buy the large size or the medium size of laundry detergent. You remember the price of each and then do a mental calculation of the price per ounce to decide which item to buy. By the time you turn down the next aisle, you've probably forgotten the prices because you no longer need this information.

Short-term memories are supposed to be fleeting. They turn over at a high rate because new ones are continually replacing them, and there is only so much information you can keep in mind at once. Research shows that most people can hold only about five to nine unrelated bits of information in mind. That's why it's easier to remember a seven-digit phone number than a much longer number, such as the account number on your credit 2 card.

Test Your Short-Term Memory

An excellent way to test your short-term memory is to see how many numbers you can remember either in a sequence or in reverse sequence. The more numbers you can remember in the proper order (or in the reverse order), the better your short-term memory is. It's harder to remember numbers in reverse sequence because this involves using your working memory—the "scratch pad" of your short-term memory. You must first remember the numbers in sequence and then transpose them. Remembering eight or more numbers in sequence and seven or more in reverse sequence would be impressive.

Although this memory test and others in this book are part of a battery of tests that are used in clinical evaluation, I want to make it clear that taking these tests will not enable you to make a valid diagnosis on your own. Making a diagnosis is a complex process that takes into account a broad spectrum of information about you. The purpose of the memory tests in this book is to give you some indication of how various aspects of memory are assessed. If you are worried about your memory, it's important that you talk with your doctor about your concerns.

Digit Span Forward

First, have someone read the first—and shortest—sequence of numbers at a rate of one digit per second. Then, recite them back in the proper order. Repeat this routine with the next line of numbers and the one after that and so on, until you fail two series in a row. (You can do this test alone by reading each line of numbers and then covering them up and writing them down in order.)

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Test Your Short-Term Memory, continued 5-0-1-7-4-9-6-3

Digit Span Backward

This test is harder than the first one because you have to use your working memory to remember the proper sequence of numbers long enough to figure out the reverse order. Have someone read the first line of numbers. Then recite them back in reverse order. For example, for the sequence 5-8-2-4, the right answer is

4-2-8-5. (As with the previous test, you can also do this one on your own by reading a line of numbers and then covering it up and writing down the numbers in reverse sequence.)

You can get a sense of how keen your short-term memory is by determining the longest numerical sequence you can remember. The longer the sequence, the better the memory. You can also use these tests to see how much your memory improves after you use the techniques I recommend in this book, especially the "chunking" strategy in Chapter 10.

The fleeting nature of short-term memory is actually beneficial because it allows you to discard unnecessary information. If you kept every short-term memory, your mind would become so overloaded with trivia that you would have trouble retrieving memories that are really important.

In his 1968 book, The Mind of a Mnemonist: A Little Book About a Vast Memory, the famous Russian neuropsychologist A. R. Luria describes a case in the scientific literature of a man (whom he calls S) who had a seemingly limitless capacity to remember detail—but this talent undermined his ability to lead a normal life. S retained so much information that he could not organize it into meaningful categories. He was utterly unable to set priorities, establish goals, and, really, live his life. In the end, S is a tragic figure, inhabiting a confusing world crammed with useless information and devoid of the meaningfulness and social connectedness that make life worth living.

Aside from having limited capacity, the brain system that handles short-term memory is also functionally fragile. Like a bubble that pops in a gentle breeze, a short-term memory is 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 that you'll forget the phone number and have to look it up again. That additional information (the question) is sufficient to make the short-term memory vanish. To borrow another metaphor from computer technology, when new information enters the brain's short-term "buffer," older information is nudged out of the buffer and into cyberspace.

Long-Term Memory

Long-term memory consists of bits of information that your brain stores for more than a few minutes and then retrieves when needed. Put another way, long-term memory is the sum 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 events that occurred decades ago. It includes the routine information that 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.

The difference between short-term and long-term memory isn't just a matter of persistence but is also one of capacity—how much information the brain can handle. Although the brain can juggle only a few short-term memories at a time, its capacity for long-term memories is virtually limitless. Barring disease or injury, you can always learn and retain something new.

Long-term memories are also less fragile than short-term memories, which means that they remain more or less intact even when something interrupts your train of thought. I'll say more about the "more or less" aspect a little later on in the book. But as a preview, let me say that long-term memory is not like a video recording, such that a moment is captured and inscribed, forever unchanging, to be replayed identically the tenth time as well as the one thousandth. Memory for specific events and experiences is dynamic; it tends to change in both subtle and critical ways over time. As new experiences accrue and new memories are formed, older memories seem to shift and reconfigure, kaleidoscopically.

For example, you may have first encountered your future spouse decades earlier in an everyday interaction—a brief business meeting involving her company and yours. You were preoccupied with finalizing a major contract with a new client and barely noticed the woman sitting across the table. Three months later, you were introduced at a party and fell head over heels in love. You began dating and then married two years later. It's now your twentieth wedding anniversary, and you're reminiscing about how you met. You think back to the first encounter in the business setting—only when you think of it now, your memory is of being love-struck at that moment.

How you remember something is largely determined by who you are. Who you are reflects the interplay among a huge number of variables that form your personality. Add to that the totality of your lifetime of experiences and associated memories. To make matters even more complex, who you are changes to some extent across time. So what you remember and how you remem-6 ber it will also change.

How you experience and then remember something is also shaped by your relative position in an unfolding event—your observational perspective. Your perspective is critical in determining what aspects of an event you attend to, as well as how you interpret them. Two people involved in an interaction are witnessing it from different perspectives. The specific observational perspective as well as the unique psychological makeup of each person will have a lot to do with how each participant perceives and remembers the interaction. This phenomenon has been dubbed the Rashomon effect, in acknowledgment of Akira Kurosawa's 1950 cinematic masterpiece Rashomon, which tells the story of an event from the perspective of four people who participated in it, each with a fundamentally different recollection of what happened.

Not all long-term memories last forever, even in a shifting state. Some long-term memories that go unused or become irrelevant fade over time. Have you ever read a book that you loved but years later found that you couldn't remember 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. Many adults I know are surprised by their ability to remember minute details of their childhood—an unjustified punishment they received, a fifth-grade science project, a room where they slept during a family vacation.

Your long-term memories fall into either of two general categories: declarative memory and procedural memory. Remembering the time and place of your lunch appointment next week (declarative memory) is different from remembering how to ride a bicycle (procedural memory). Declarative memory is more vulnerable to the effects of age, as well as of brain illnesses (such as Alzheimer's disease), than procedural memory.

Declarative Memory

Declarative memory includes information that requires you to make a conscious effort to recall. Another name for this type of long-term memory is explicit memory. There are two types of 7

Flashbulb Memory

Where were you at the moment you first heard about the attack on the World Trade Center? Whom did you talk with? What did you do next? All of the details that you recall constitute a flashbulb memory, a term that researchers use to describe an extremely vivid memory for an unexpected, emotionally charged public event. The assassination of President Kennedy, the Challenger space shuttle disaster, the September 11 terrorist attacks—images of these events became ingrained in the memories of millions of people who witnessed them, either directly or by means of television and other mass media.

Flashbulb memories tend to include numerous minute details of your experience of an event: weather conditions, what you were doing at the moment, who was near you, and so on. It's likely that the combination of profound meaningfulness and emotional impact surrounding the event helps sear it into your long-term memory. The psychological power of these types of events activates the amygdala, a structure within the brain's memory system that plays a major role in emotional processing.

It's long been assumed that flashbulb memories are more accurately and consistently maintained over time than are memories for ordinary experiences. But research shows that recollection of powerful events may also be vulnerable to distortion and reorganization over time.

A well-known study investigated long-term memory for the Challenger space shuttle explosion, which occurred in January 1986. One hundred six people completed a seven-item questionnaire one day after the tragedy regarding where they declarative memory: episodic and semantic. Episodic memories are linked to events that occurred at specific times and in specific places. The party you attended last weekend, the vacation you took last summer, a movie you saw twenty years ago—these are 8 all episodic memories, events bound in a specific temporal-spatial were, whom they were with, what they were doing, and so on, at the time they learned of the explosion. Approximately three years later, forty-four of the original participants were located and asked to respond to the exact same set of questions. The average accuracy score was three out of seven, and 25 percent of the respondents were wrong on every single item! Despite this low degree of accuracy, the participants rated their confidence in the correctness of their responses at greater than 4 on a 5-point scale.

More recently, scientists from Duke University compared people's memory for the events of 9/11 with their memory for other, ordinary episodes. The scientists asked people what they remembered about these two sets of events at intervals of one week, six weeks, and thirty-two weeks after they occurred. Although the study participants rated their 9/11 memories as much more vivid over time and believed that their recollections were more accurate than for the everyday episodic memories, the researchers found that the accuracy or consistency of the memories was similar for the two sets of events.

What this research tells us is that flashbulb memories are subject to the same biases and distortions that affect other long-term episodic memories. But even though they're imperfect, flashbulb memories are probably among the longest-lasting memories we have because they tend to be imbued with emotional significance and because they frequently entail catastrophic events that are kept in the public eye for an extended period of time. A flashbulb memory is re-evoked each time you see a reference to it in the newspaper, on TV, in a film, or in a history book.

context. When you revisit an event memory, you recall temporal information (when it happened) and spatial information (where it happened) about it.

Semantic memory is factual knowledge. Your semantic memory consists of much of the basic information you learned during 9

your school days, along with an assortment of other facts, such as your mother's name, your address, or the meaning of the word winter. Unlike episodic memories, semantic memories aren't bound by time or place. You can't point to the moment when you learned your mother's name, for example. And even if you do know when you learned the multiplication tables or the name of the first president of the United States, the timing isn't important to your knowledge or recollection of these facts.

Procedural Memory

Procedural memory refers to, well, procedures: the skills and routines that you draw on automatically to perform actions like getting dressed, shuffling a deck of cards, or piloting a jet. Evidence of intact procedural memory is implied in the accurate performance of a skill or behavior. Even though your recall of procedural memories is relatively effortless, each one of them required effort and practice to learn. But ever since you mastered the skill involved, you've been able to perform it without necessarily remembering how you learned it or the separate steps entailed. When you take out your bicycle for a ride, you don't say to yourself, "OK, first I straddle the seat, then I put my left foot on the left pedal . . .," and so on. You just get on and go. It's as though your body does your thinking for you.

The old saying "You never forget how to ride a bike" appears to be largely true. Procedural memories don't fade or change much with age. You may feel a bit rusty if you haven't ridden a bicycle or played the piano in a while. But you don't have to relearn these skills all over again. With a bit of practice, the skills and routines come back to you. Even people with Alzheimer's disease can perform many routine tasks until the advanced stage of the illness. Scientists believe that procedural memory is robust because it is stored widely throughout the brain and because it is not dependent upon the hippocampus, one of the memory structures within the brain that is particularly vulnerable to the effects of normal aging.

Making Memories

Now that you know about the different types of memories and which ones are most likely to be affected by aging, we'll move on to the process of remembering. In Chapter 2, you'll learn step-by-step how memories are made in the brain: what happens when you first encounter new information, how the brain processes and stores that information, and how you are able to call up the information when you need it. You'll also learn some strategies for giving your memories staying power.

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