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  3. The Magic of Memory —By Laurence Cherry Our memories are

The Magic of Memory —By Laurence Cherry Our memories are

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问题                               The Magic of Memory
                                                                    —By Laurence Cherry
    Our memories are probably our most cherished possessions. More than anything else we own, they belong uniquely to us, defining our personalities and our views of the world. Each of us can summon thousands of memories at will: our first day at school, a favorite family pet, a summerhouse we loved. And yet the marvel of memory continues to be a tantalizing (挑逗性的) mystery. Nevertheless, within the past few years great advances have been made in understanding what memory is, how it works, and how it may possibly be improved. "We’re standing at the brink of a whole new era in memory re search," says Dr. Steven Ferris, a psychologist at the Millhauser Geriatric (老年医学的) Clinic. "For the first time, there’s a general feeling that we’re really on the right track."
     For years, the prevailing theory was that remembering was somehow connected to electrical activity inside the brain. But within the past decade, it’s become clear that chemical changes must also be involved, otherwise our memories could never survive deep-freeze, coma, anesthesia (麻醉) and other events that radically disrupt the brain’s electrical activity. Ingenious re search over the past few years has demonstrated that biochemical changes do indeed accompany learning and remembering. In one dramatic experiment, mice, who usually prefer the safety of darkness, were taught to fear the dark and were then killed. Extracts of their brains were injected into untrained mice, and they then began to shun the dark. Other experimenters have shown that the amounts of certain chemicals, such as RNA (核糖核酸), radically in crease with learning, as do the amounts of certain neurotransmitters (神经传递素 )—chemicals released by brain cells that help conduct nerve impulses from one brain cell to another. Memory, then, is also chemical in nature, al though exactly in what way remains a mystery.
    Almost all memory researchers now agree that our brains record—and on some level remember—everything that ever happens to us. Many people who’ve narrowly escaped sudden death, such as soldiers and mountain climbers, have reported that in the few seconds that seemed left to them a stream of long-lost memories flashed before them. The first experimental confirmation that the brain does record every experience in this minute way came some years ago from Dr. Wilder Penfield of the Montreal Neurological Institute. He hoped to cure epileptics (癫痫病人) by stimulating a part of their brains called the temporal cortex (脑的颞皮层) with a mild electric current. Because the brain is immune to pain, Penfield was able to operate with his patients fully awake. To his astonishment, simply by touching the brains of some patients with the tip of his wire-thin electrode (电极) he was able to evoke astonishingly precise and vivid memories. "I see a guy coming through the fence at the baseball game," exclaimed one patient, whenever Penfield touched the upper part of his left temporal lobe (脑叶). "It’s the middle of the game, and I’m back there watching him)" Another woman reported being back at a con cert she had once attended and could even hum along with the orchestra whenever her brain was stimulated.
    Investigators using hypnosis (催眠术) have been as astonished as Penfield at the amazing capacity of our memories. Once in a trance (昏睡), good hypnotic subjects can report detailed recollections of events that took place days, months, even decades ago—which, when checked against old records and diaries, turn out to be accurate. "Everything, absolutely everything, is remembered," says one hypnotist.
    Even senile patients, who can hardly remember recent events at all, retain the ability to remember new experiences, but only very briefly. "Give them a list of nonsense syllables to memorize, and for a few seconds they do almost as well as healthy young people in remembering," says one expert. But apparently the brains of senile subjects cannot electrochemically translate the new information and shift it into long-term storage. It seems rather as if our perceptions, in order to be remembered for more than a few seconds, must be sorted out and slid into place like folders into file cabinets. Some of the cabinets are easily opened, their contents readily available to us. Others, thanks to still unknown processes, are locked away, only to be retrieved if the files are jarred open by hypnosis or a researcher’s electrode.
    For years, scientists hunted for the brain’s elusive "memory center," where long-term memories might be processed and stored. Above all, the hippocampi (侧脑室下角的海马状突起物), small, seahorse-shaped structures about three centimeters long, deep within each half of the brain, were target ed as the possible center. If one hippocampus is injured, memory is temporarily affected, then eventually returns. But if both are damaged, the loss of memory is final. Patients who have lost their hippocampi live in a strange, twilight world. If they meet you, they will shake your hand and five minutes later greet you as a complete stranger. Although they can still perform well enough on IQ tests and speak quite intelligently, it’s as if some crucial memory system had been cruelly short-circuited. Often they’re aware something is wrong and try to hold on to their memories. But the attempt is usually use less, and even when they forget the reason for their sadness, they remain de pressed.
    Is it possible to improve your memory?
    The surprising answer appears to be yes. Dr. Richard J. Wurtman, professor of endocrinology (内分泌学) at the Massachusetts Institute of Technology, recently discovered that the food we eat can affect the amount of neuro transmitters in our brains and—by implication—how well we can remember.
    In 1985, Wurtman and his colleagues learned that choline (胆碱), a common food substance found in large quantities in egg yolks (and to some degree in meat and fish as well), has a pronounced effect on the brain’s ability to make an important neurochemical called acetylcholine (乙酰胆碱), al most certainly involved in memory.
    Meanwhile, new information is being gathered about memory loss among older people. With the exception of an unfortunate minority who suffer from Alzheimer’s disease, a progressive ailment that leads to almost total memory loss, the news is good. "I think the most crucial thing we’ve learned is that it simply isn’t true that you lose your memory as you get older," says Dr. James Ninninger of the Payne Whitney Psychiatric Clinic. "That’s simply one of the self-fulfilling prophecies that should be dropped." At Johns Hopkins University, studies of men over many years as they grow older confirm this belief. "There are some subjects sixty-five to ninety who are just not showing any decrements," says Dr. Nathan Shock, who admits that the findings surprised him.
    Although some brain changes do seem to come with age, in most cases their effect on memory is not nearly as serious as once thought. Even the idea that we begin to lose hundreds of thousands of brain cells each day past the age of 30   with the usual grim implication that our brainpower must diminish- has recently been hotly disputed. "As a neuroanatomist (神经解剖学家 ), I’ve been intrigued by this myth of disappearing brain cells," Dr. Mari an C. Diamond, professor of anatomy at the University of California at Berkeley, has said. As she points out, almost no studies of brain loss have been done in humans and only a few haphazard ones in animals. "In fact," she insists, "there is only a trivial decrease in the number of brain cells— right up through old age."
    Another recent finding is that intellectual stimulation keeps memory at its peak—just as physical exercise does for our muscles. In the Johns Hopkins’ studies, the people who showed the least memory impairment as they aged were those who had made problem-solving a way of life. Studies in monkeys and rats have shown the same thing: constant mental activity pre serves memory. And at least until we reach the outer limits of old age, the continuous amount of new information we are always storing should help us to remember, not cause us to forget. Dr. Patricia Siple, a psychologist at the University of Rochester, has found that a large store of information helps our memories. We remember not so much words and sounds as concepts, which form a kind of indexed system to recall information.
    Recent research indicates that, unlike a container that can be filled, our memory far more resembles an ever-growing tree, continually putting out new roots and connections, memory building on memory, rivaled in complexity only by the mysterious, ever-challenging brain itself.
The author compares our memory first to "file cabinets" (Paragraph 5) and then to an "ever-green tree" (the last paragraph). This special comparison is known as
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