Think Smart: A Neuroscientist's Prescription for Improving Your Brain's Performance (11 page)

Despite its tiny size, the hippocampus is one of the most powerful structures of the human brain. Everything you ever learn wends its way through this portal prior to its distribution throughout the remainder of the brain. If your hippocampus is damaged as a result of a stroke or traumatic brain injury, you can no longer establish new memories, as happened with H.M. A similar but less severe failure occurs with depression. As part of the depressive experience, the hippocampus atrophies and memory failures become commonplace, often leading to an incorrect diagnosis of dementia. But whatever the cause, impairment of the hippocampus causes newly learned information to drift off a person’s mental horizon after only a few moments. What’s worse, this drift into mental oblivion can’t be prevented despite a person’s best efforts.

In my office I routinely test hippocampal function in those patients I suspect may be suffering from damage in that area. I ask them to learn and retain five simple words, such as
apple, tie, pen, house,
and
car.
Even severely affected patients can initially repeat the words back after a few attempts. The problem arises when I ask them to repeat the words again after a five-minute delay; those with hippocampal failure can’t remember more than one or, at best, two of the words. Persons with normally functioning hippocampi, in contrast, can usually manage to come up with all five of the words. People with damage to the hippocampus perform so poorly because their brain can’t encode the test words—a prerequisite for holding them in short-term storage.

According to recent research, both the recollection of past events and the imagining of future ones require a normally functioning hippocampus. For instance, one fMRI study of healthy volunteers revealed that recalling past experiences and imagining future experiences activates a similar network of brain regions, including the hippocampus. As further proof of a memory-imagination link, people with faulty memories secondary to dysfunctional hippocampi have difficulty imagining anything that hasn’t actually happened. For example, those with hippocampus-related memory problems do poorly when imagining a meeting with a friend on a specific street corner or dining with a friend in a familiar restaurant. It’s as if both the imagined and the recollected world are rendered in shades of gray instead of vivid color.

This new discovery of a link between memory and imagination was anticipated in Greek mythology where Mnemosyne, the goddess of memory, gives birth to the muses, a sisterhood of spirits who inspire the creative process through remembrances. It also suggests a
strategy: the use of memory exercises as a means to foster imagination and vice versa.
Creative-writing teachers have always had an intuitive feeling for this approach. They encourage their students to provide from memory highly specific details about the places and people they have known. This enables the writer to create in his or her imagination more memorable scenes and characters. Using this technique, the author can render his fictional creations with greater believability since they’re based on real people and places that he remembers from previous encounters. In order to provide remembered details about real places and people, the writer calls upon the hippocampus.

Since strengthening memory also increases imagination and creativity, it’s worth the effort required to develop a superior memory.

Let’s start with the simplest memory exercise of all: repeating something that has been heard just moments earlier.

Forward digit span:
Ask a friend to read to you in succession strings of numbers, starting with five-digit spans and working upward (six digits, seven digits, etc.) until you can no longer correctly repeat back the number sequence. He or she should say the numbers in a steady monotone, taking care not to group the numbers. When they’ve finished, repeat the numbers back in the precise order.

If you prefer to do the exercise by yourself, read in succession five-, six-, seven-, and eight-number strings into a recorder and a few hours later listen to that recording of yourself reading the number strings one at a time. After hearing each number string, say it aloud and write it down. When you’re finished, reverse the recording and listen to your response and check it for accuracy. If you correctly recited the five-number string in its precise sequence, go on to a six-number sequence, then seven, then eight, etc.

As an alternative, you can test visual rather than auditory recall by looking at number strings instead of listening to them. Write out the numbers zero through nine on separate two-by-two-inch pieces of paper and paste each of them onto cardboard or plastic. Place the numbers facedown on a table, select five of them, and then turn them over and randomly line them up in a straight line. Look quickly at the numbers and then turn away and write them down from memory. Look back at them and check your accuracy. Then proceed to six-, seven-, eight-, and nine-number strings.

When listening to the numbers and repeating them back, the longer your digit span the better your auditory processing. The same holds for visual processing: the longer the string of numbers you can write down after reading them the better your visual processing. As a side benefit, comparing your auditory and visual performances provides a quick and informal way of determining if you are primarily a visual or an auditory learner. In addition, forward digit span—either listening to or reading the numbers—is an excellent means of enhancing focus and concentration. Even more important, it’s possible to increase one’s digit span by practice.

It may surprise you to learn—as it did me—that the average digit span for normal adults is only between five and seven. A two-year-old has a digit span of two, a three-year-old a span of three, a four-year-old a span of four, etc., up to a span of seven for a seven-year-old. In other words, the average digit span for adults is set by age seven—and this holds true not just for English speakers but also for native speakers of other languages. It seems that the brain isn’t designed for spontaneous encoding into short-term memory of more than seven items. If you want to do better than that, you have to practice.

At this point you might wonder, “Why would anyone bother? So what if I can learn to increase my digit span?”

Despite its simplicity, digit span reflects the efficiency of the earliest stages of information processing within the brain. This is important because how well you learn depends on how efficiently you process information at the earliest stages (the basis for short-term memory). Heightened attention enables you to increase the amount of information that your brain can take in (as mentioned in the discussion of sensory memory). If you increase your digit span, you can improve your brain’s performance. We know this because digit span has been found to be a reliable predictor for early math and reading proficiency. The same holds true for performance on standardized tests.

Nor should it be surprising that increases in digit span correlate with enhanced brain performance. Among the brain functions activated are attention, concentration, sequencing, number facility, and auditory and visual short-term memory.

Backward digit span:
Repeat the previous exercises, but this time recite the numbers in reverse order. If you’re doing the exercise by yourself, it’s especially important to record your responses and check them for accuracy, since it’s easy to make errors toward the end of the backward digit span exercise (when you are recalling the first few numbers of the sequence) and not be aware of your failure.

If you carry out both the forward and the backward digit span exercises, you’ll appreciate how much harder it is to mentally “read” the numbers in reverse. While many people can accurately recite seven digits forward, few people can manage more than five digits backward. Try it yourself. The reason for that difference? Backward digit span involves not only the registration and encoding of numbers but also their manipulation. You have to envision the numbers in some way—depending on the memory technique employed—and then “read” them from right to left rather than following the usual practice of reading the numbers from left to right. In addition, different brain functions are involved. While attention and auditory short-term memory are called into play with forward digit span, attention and working memory are used in backward digit span.

Working memory is the ability to hold information “online” for later retrieval while turning your attention to something else. For example, when you’re on the phone and momentarily pause in your conversation in order to answer a “call waiting,” it’s your working memory that enables you to pick up where you left off when you return to the original call. Similarly, when you reverse the digit span, moving leftward from the last number to the first, you must hold in working memory the first few digits in the string in order to repeat them at the end.

Similar difficulties occur when reversing words. Mentally spell the word
world
backward. You should have no problem doing that. Then spell
hospital
backward. If you did that correctly (be certain to use your voice recorder to check for accuracy since the
p
and the
s
are frequently transposed), try
administrator,
then
equestrian.
Most people can manage
hospital
and
administrator
but flounder when backward spelling
equestrian.

Notice that
administrator
contains thirteen letters, eight more than the five-digit upper limit for numbers that most people can comfortably reverse. There are two main reasons why we’re better at reversing letters than numbers. With the exception of mathematicians, most of us spend more time working with letters and words than we do with numbers. In addition, words often represent something while a string of numbers is meaningless—unless we can impose a meaning by using one of the memory techniques described next.

Obviously, few of us spend much time during our everyday lives memorizing lists of digits and repeating them, either forward or backward. Most of the time, we’re learning new information from other people, e-mail, the Internet, or other sources. This is the kind of memory we’re enthusiastic about improving. Further, cultivating the art of memory can balance our overreliance on written sources of information.

In Plato’s
Phaedrus,
Socrates recounts the judgment of the Egyptian god Thamus on the invention of writing by the god Thoth: “This invention will produce forgetfulness in the minds of those who learn to use it, because they will not practice their memory. Their trust in writing, produced by external characters which are not part of themselves, will discourage the use of their own memory within them.”

Although it’s a long trip from the early Greeks to the BlackBerry, Socrates’ warning remains relevant today. As we become more dependent on memory aids, our natural mnemonic powers are atrophying from disuse. And this leads to a vicious circle: as memory deteriorates, we rely on storing more facts on paper or, as is increasingly common, on electronic devices, thus further weakening our memory powers. If you want to think smarter, you have to make active efforts to strengthen your memory and reverse this process.

All techniques to enhance memory involve the imposition of
meaning
on the information we wish to remember. For instance, memorize the following list of numbers by reading it aloud just once, then look away and try to recall the numbers in their exact order: one, four, nine, one, six, two, five, three, six, four, nine, six, four, eight, one. Most people can manage about seven of the fifteen numbers. You can, however, recall all of them if you first convert them into single digits (1, 4, 9, 1, 6, 2, 5, 3, 6, 4, 9, 6, 4, 8, 1) and observe that they can be grouped to represent the squares of numbers one through nine: 1, 4, 9, 16, 25, 36, 49, 64, 81.

Another way of increasing your recall is to focus on the meaning of something you are trying to memorize. In a famous experiment carried out in the mid-1970s, volunteers were asked one of three types of questions about a series of words they were requested to memorize. One question concerned the word’s visual appearance (“Uppercase or lower-case letters?”). A second question focused on the sound of the word (“What does it rhyme with?”). The third type of question probed the meaning of the word. When later asked to recognize the words from a list, those who had encoded the words according to meaning greatly outperformed those who encoded according to visual appearance or sound.

Various methods have been suggested over the centuries to improve memory by meaningfully encoding the material to be memorized. Most of them can be traced to an unknown teacher in Rome who around 86-82 B.C. compiled a list for his students of specific techniques.

According to this teacher, who described his method in the
Rhetorica ad Herennium,
the “art of memory” involves skillfully linking the items to be remembered with places and images. If you want to remember a grocery list using this method, you create a mental picture of a familiar room and then place the objects you want to remember at select locations within the room. You then imagine yourself walking through the room and observing the objects at the locations where you placed them. You can rapidly confirm the power of this method for yourself.

Think about your living room. Envision as many details as you can about it. Then mentally place the following objects at various places in the room (above the fireplace, on a favorite chair, on the coffee table): log, candy, wallet, comb, pen, tie pin, ring, watch, and shoe. Take care to clearly envision the object at its “locus” (site) within the room. The clearer your image, the more accurate your recall will be.

Alternative methods employ the story system. Imaginatively weave together into a coherent story the items to be remembered. The more vivid, colorful, novel, and even bizarre the story, the greater your chances of remembering your list. For instance, for the list mentioned above, imagine a log dressed like a man walking along the street eating candy. The log is quite dapper and is decked out in an expensive suit and Bruno Magli loafers. His solid 18-karat-gold accessories (tie pin, ring, pen, and watch) gleam in the sunlight as he smugly struts along, the quintessence of self-satisfaction. But all is not well. Sneaking up behind him is a pickpocket pretending to be combing his hair while slipping his hand in the log’s back pocket, from which he extracts a fat wallet. If you fix that image clearly in your mind, you’ll be able to recite the list an hour, a day, or a week from now. That’s because the story links the words into a vivid quirky image that is easy to remember.