Think Smart: A Neuroscientist's Prescription for Improving Your Brain's Performance (13 page)

4.
Create your own memory aids based on the details of your life experience.
The goal is to capture unfamiliar information by linking it with images of things that are unique to you, e.g., the layout of your living room or other familiar location. With this method you have only to place the information you want to learn at key locations within the room and then retrieve it by mentally strolling through the room.

5.
Learn a list of memory pegs
that can be used for numbers. One example is on page 105, but you can easily come up with your own associated rhyming words.

Finally, a few words about forgetting. Why do we forget? “Memory decay” over time was a formerly popular explanation. But blaming everything on the passage of time isn’t a satisfactory explanation. It’s like explaining rust on a car as resulting from the passage of long periods of time. Rust results not from the passage of time but from the oxidation processes that occur in the metal. Like rust, forgetting requires something in addition to the mere passage of time. Forgetting as a simple by-product of time-linked decay is also contradicted by the fact that sometimes memories recover over time, or can be resurrected by reminiscence, psychotherapy, or other techniques.

Currently the most popular theory of forgetting is
retroactive interference:
new information interfering with and supplanting older information. For instance, do you remember what you had for lunch five days ago? Unless the lunch was a special occasion, you’re unlikely to be able to distinguish it in your memory from all of the other lunches you’ve had over the past week. The more active your life, the more difficult it will be to overcome retroactive interference. Which leads to a marvelously effective memory exercise: remembering similar situations by mentally linking them via distinguishing characteristics, however subtle. For instance, even though the food may have been unremarkable at any particular lunch, the discussion or the information gained or some other aspect of that lunch can make the total experience—including what you ate—stand out in your memory. The key is to discover or create that distinguishing feature. Let’s take up a few ways of doing that.

Have you ever wondered why telephone numbers are seven digits long? Because, as first pointed out by the nineteenth-century philosopher Sir William Hamilton, people generally experience difficulty with numbers containing more than seven digits: “If you throw a handful of marbles on the floor, you will find it difficult to view at once more than six, or seven at most, without confusion.”

Hamilton’s homespun experiment was confirmed in a 1956 paper by Princeton University psychology professor George Miller, “The Magic Number Seven, Plus or Minus Two.” Miller found that those who exceed that seven-digit span do so by breaking the number into groups of smaller numbers of recognizable sequences or words, a process he called “chunking.” For numbers exceeding seven digits, chunking is an indispensable tool. Even seven-digit numbers such as telephone numbers are broken up into two “chunks”: the first three numbers interrupted by a pause (for spoken numbers) or a space (for written numbers), followed by the last four numbers—the memory method used by Scott Kim described earlier. For international calls, several additional chunks must be memorized.

Chunking makes it easier to keep all previous numbers “in mind” as each succeeding number is encoded within the brain. For instance, when someone tells you a telephone number, you won’t be able to dial it unless you can keep in mind the correct sequence from start to finish. This process of encoding one item while retaining access to items encoded moments earlier depends on
working memory.
It is as a rule considered the basis for general intelligence and reasoning, since people who can hold the greatest numbers of items in mind are best equipped to consider multiple aspects of a problem simultaneously.

Word processing on your PC provides a good analogy for what happens during failures of working memory. When you switch from one document to another on your word processor, the unattended document is still accessible. All you have to do is toggle from document 1 to document 2 in order for you to keep both of them “in mind.” But if you close one document as you move to the second document, that first document is no longer available for immediate retrieval. A failure in working memory is like that: you close the first document when you switch to another instead of holding that first document online.

For instance, if you’re interrupted by an intercom message from your secretary at the moment you’re about to make an important point with an employee during a meeting in your office, you may discover after taking that message that you’ve forgotten what you had intended to say before the interruption. This “interference effect” results from a failure in “working memory.” You inadvertently closed the first document (the point you were intending to make during your in-office discussion) when you moved to the second document (the intercom message from your secretary). As a result, when you returned your attention to the office conversation and attempted to retrieve what you intended to say before the interruption, you drew a blank.

The greatest enemy to people’s working memory is distraction. If you’re thinking of something else and aren’t really listening when you are told a telephone number, the sequence won’t be encoded in your brain. Later, you won’t be able to retrieve it because distraction during the initial encoding process interfered with memory consolidation.

Multitasking, despite its inefficiency, has the potential to strengthen working memory as long as people make a deliberate effort to keep the multiple tasks “in mind.” As the skilled multitasker switches from one activity to another, if he’s adept enough he retains the first activity in working memory. As a result, in contrast to the example of the interruption during the meeting, the skilled multitasker has no problem remembering the point he was about to make just prior to the interruption.

Working-memory deficiencies underlie the distractibility and poor academic achievement of people, adults as well as children, who have attention deficit/hyperactivity disorder (ADHD). Reading problems also result from working-memory problems: the earlier words in a sentence can’t be recalled by the time the reader reaches the end of the sentence.

Many of the classic memory exercises are actually exercises of working memory. Here’s an example of one that I use in my office to test my patients’ working memory: Memorize these four items:
apple, charity, Mr. Johnson, tunnel.
Now set a chronograph or other timing device for five minutes and return to your reading. When the alarm goes off, recite aloud the four items. To do that you had to keep the items in a kind of suspended animation: available for recall and yet not so much “in mind” that they interfered with your ability to understand the pages that you read before the sounding of the alarm signaling that you should recall the items.

In order to distinguish working memory from memory in general, think of it this way: If you’re required, as in the above example, to hold certain items “in mind” while you turn your attention to something else, you’re using working memory. If you’re simply asked to recall something from the past (“Who was the sixteenth president of the United States?”), that is a test of general memory. Working memory is also called upon whenever we mentally manipulate information. For instance, memorize these numbers: 238538392. Now, as an exercise in working memory, rearrange that sequence from lowest to highest (223335889) without writing anything down.

As another example of the general memory-working memory distinction, recall the names in order of all of the presidents since Harry Truman. That is an exercise in general memory. Now with the list firmly in mind, rearrange the names in alphabetical order without resorting to pencil and paper (Bush, Bush, Carter, Clinton, Eisenhower, Ford, Johnson, Kennedy, Nixon, Reagan, Truman). In this exercise you’re exercising working memory to mentally carry out the rearrangements.

Admittedly, sharp distinctions can’t always be made between general memory and working memory. Often we call on both kinds of memory at the same time. For example, if you’re aware of all of the cards in play during an ongoing game of bridge, you’re exercising your working memory; if you’re thinking about how things went when you held a similar hand in a game you played several months ago, you’re using general memory.

Working memory
and
general memory
also involve different brain pathways. Information held in general memory is initially encoded in the hippocampus for later distribution to the temporal lobes and other portions of the two hemispheres. And since general memories are distributed throughout the brain—rather than encoded within a “memory center”—forgetting is a gradual rather than a sudden process.

For instance, you don’t suddenly forget all of the details of your college graduation. Instead, with each passing year your general memory becomes less precise and reliable. That’s because the memory of your graduation is widely distributed throughout your brain rather than localized to a specific area. This widespread distribution has led psychologists to compare general memory to a hologram, a laser-generated three-dimensional image.

Holograms differ from ordinary photographs by nature of the fact that the entire image can be reconstructed from portions of the hologram. If you divide a hologram into two or more pieces, the resulting image depicted on the parts become less distinct. It doesn’t disappear altogether even when the original photo is divided many times. General memory is like that too, because of its wide distribution throughout the brain.

Working memory,
in contrast, is formed at a later point in the information flow. After encoding in the hippocampus and wide distribution throughout the rest of the brain (principally the two hemispheres), working memory is maintained in an active state within the frontal lobes, specifically the dorsolateral prefrontal cortex. As working memory improves, the rate of glucose metabolism
decreases.
The explanation for this decrease?

The decrease in brain activation that is associated with improved performance suggests that with practice our brains don’t have to work as hard to achieve improved performance. The process can be compared to learning to drive a car. The more experienced you become in driving, the less conscious attention and concentration you have to exert. On the basis of your previous driving experience, you’re able to monitor and respond to nearby traffic without thinking consciously about how you’re doing it. An fMRI of your brain taken while you’re driving would show decreasing activity in the dorsolateral prefrontal cortex as your driving skills increase. A similar decrease in brain activation occurred in an experiment involving volunteers learning to play a computer game. Initially their prefrontal glucose metabolic rates were high. But after they became proficient at the game, their scans showed significantly lower rates of glucose metabolism.

Since working memory is carried out primarily by the frontal lobes, and these areas are especially vulnerable to atrophy because of disuse as we age, it’s important to do everything you can to enhance working-memory skills. A double benefit derives from practicing working-memory exercises: the exercises prevent deterioration of the frontal lobes, which, in turn, increases your capacity to further enhance your working-memory skills.

Given its importance for optimal brain function, let me suggest
a series of exercises that can strengthen working memory:

Gather a handful of pennies, nickels, dimes, and quarters and scatter them on a desk or table in front of you. You shouldn’t count the number of coins ahead of time, but the desired number is anywhere between ten and fifteen of each, laid out in no particular order. Now pick them up one at a time and total the number of coins of each denomination. How did you do it?

Unless you have a highly developed working memory, you picked up one denomination at a time and totaled it before moving on to another denomination. It’s unlikely you elected to pick up the coins at random while keeping a separate mental tally for each denomination and then totaling everything at the end. That’s because it requires greater mental effort to keep track of all of the different denominations simultaneously. It’s easier to count the coins one denomination at a time because that process makes fewer demands on working memory. After counting the nickels, for instance, that total can be stored in working memory and your attention shifted to the next denomination.

In order to increase your working memory, count the pennies and nickels at random (i.e., don’t alternate them). This will require you to keep a running total of each denomination in working memory while you’re counting. Do it rapidly and as you count each coin, place it to the side. When you’re finished, write down your totals and then check for accuracy by separately counting each of the denominations among the discarded coins. Not much practice should be required for you to manage two denominations.

Next, count three denominations (pennies, nickels, dimes) in the same manner, and then count all four denominations. If you can manage four, you are achieving what is considered by psychologists to be the maximum. “Four items seems to be the limit. It’s a fundamental characteristic of human working memory,” according to Paul Verhaeghen, the psychologist at Syracuse University who carried out the experiments demonstrating the four-item limit. (If you want to read the fascinating details of how he determined this, check his 2004 paper “A Working Memory Workout: How to Expand the Focus of Serial Attention from One to Four Items in 10 Hours or Less,” published in
Journal of Experimental Psychology: Learning, Memory and Cognition,
vol. 30, no. 6.)

Let me suggest
several other exercises for enhancing working memory:
Over the span of one minute, name as many animals as you can. You can time yourself and make a tally mark for each word and count the tally marks after you’ve finished at the end of the minute. Also record your responses in order to detect duplications, since the name of each animal can be used only once. Better yet, ask someone else to make a tally mark for each word that you speak out. Twenty to thirty words is considered acceptable. Next, recite the number of cities you can think of in one minute. Then do fruits, vegetables, athletes, movie stars—whatever category allows you to choose from a vast number of potential choices in this test of what psychologists refer to as semantic (category) fluency. When finished with one category, switch to another while remaining within the one-minute time frame. For instance, alternate cities with fruits. Not all categories have been standardized; that is, there isn’t an established upper or lower limit for movie stars. But aim for somewhere in the range of twenty to thirty items for each category within the one-minute limit.