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They never forget: The strange gift of perfect memory   

2013-10-26 21:36:27|  分类: 默认分类 |  标签: |举报 |字号 订阅

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本文作者:小红猪小分队

mg21528781.500-1_300Some people can recall what happened on almost every day of their lives. Unlocking their secrets could shed light on the way all our memories work

IT WAS an email that memory researcher James McGaugh found hard to believe. The sender, a 34-year-old housewife named Jill Price, was claiming that she could recall key events on any date back to when she was about 12, as well as what she herself had done each day.

"Some people call me the human calendar," she wrote, "while others run out of the room in fear. But the one reaction I get from everyone who finds out about this 'gift' is amazement. I run my entire life through my head every day and it drives me crazy!"

McGaugh invited Price to his lab, making sure he had to hand a copy of 20th Century Day by Day, a book that lists important events by date. He opened the book to random pages and asked Price what had happened on those days. "Whether it was a plane crash or some elections or a movie star doing an outrageous thing, she was dead on," he recalls. "Time and time again."

That was in June 2000. McGaugh's group has worked closely with Price ever since, and has discovered she is one of a select few with similar abilities. These individuals are neither autistic savants nor masters of mnemonic-based tricks of recall, yet they can remember key events from almost every day of their lives. Learning more about their abilities and how their brains are wired should lead to insights into the nature of human memory.

Intrigued by McGaugh's findings, I arranged to visit his lab at the University of California, Irvine, to find out how these people live with such unusual abilities - and what it is like for the researchers working with them. "It never ceases to amaze me," says McGaugh's colleague, Aurora LePort. "Some of them can remember every day you give them." She says studying people whose powers of recall seem to be enhanced, rather than impaired, offers us a new tool to explore memory.

It is certainly fair to say that most of our knowledge of memory derives from looking at memory loss. The classic case is that of Henry Molaison (better known as "HM"), who had surgery nearly 60 years ago to treat severe epilepsy. In a misguided attempt to remove the source of the seizures, several parts of the brain were cut out, including both hippocampi, curled up ridges on either side of the brain.

For HM, the consequences were catastrophic. Although he could still recall his early life, he was no longer able to lay down memories of things that happened to him after the surgery. Every day, the researchers studying his condition had to introduce themselves anew. Intriguingly, though, he could perform tasks that used short-term memory, like retaining a phone number for a few minutes.

Thanks to HM and many other people with neurological problems caused by head injuries and strokes, we now know that there are different kinds of remembering. Our short-term memories last up to about a minute, unless they are reinforced, or "rehearsed" through further repetition. While much about the neuroscience of memory remains mysterious, our hippocampi seem to be involved in turning these fleeting impressions into long-term memories, which are thought to be stored in the temporal lobes on either side of the brain.

Long-term memories can be subdivided into semantic ones to do with concepts, such as the fact that London is the UK capital, and autobiographical memories, about everyday events that we experience. Price has no special abilities with regard to her short-term or semantic memory, but when it comes to autobiographical memory, her scores are off the chart.

Detective work

Naturally, McGaugh's team did not take Price's recollections at face value. In a routine they have since honed on other individuals, they check facts using subjects' diaries and photo albums, interviews with their families, and online research. For instance, they might check someone's description of their first home against images on Google Street View and the family photo album.

"Some of them are really good," says LePort. For instance, one subject claimed she could recall what she was thinking when brushing her teeth on a particular date. "She said: 'Oh yes, I was thinking about going to dinner.' I can't confirm that, but from all the other testing that we've done, I do believe her."

In 2007, McGaugh's team published their findings about Price in the journalNeurocase (vol 12, p 35), concluding that she was the first known case of someone with highly superior autobiographical memory (HSAM). They have since discovered 33 others with similar talents. As with Price, the detailed memories date back to around the age of ten.

Interviewing Price on the phone, I ask what it feels like to have this ability. "My memory really has ruled my life," she says. "It's brought me great joy, but it has tormented me. Being able to hold on to all of the amazing moments is something that gives me comfort. But you remember the bad things, too." Her husband died a few years ago, Price tells me, and her grief is palpable over the telephone line.

Reliving the past

The next one of McGaugh's HSAMers I speak to is more upbeat. Marilu Henner, an actor who is perhaps best known for her role in the 1980s US TV series Taxi, says her abilities have been invaluable professionally. "In acting classes, people would ask, 'How are you able to cry or to laugh so easily?' I'd be right back at that emotional moment, with all of my senses engaged, looking out through my eyes."

Price also concedes her gift helps in her job - as a religious education coordinator at a synagogue. "My memory helps me remember anything I need to know about the students," she says. "And my co-workers know that if they need anything, I will be able to find it."

McGaugh says most HSAMers see their talent in a positive light. "None of them has said they would wish away the ability if they could," he says. "When I ask what they do when they have a bad memory, they say they conjure up a happy one."

So how much, exactly, can they remember? LePort has begun a long-term tracking project to see how their memories might fade over time. Wondering how my own memory might stack up against their awesome abilities, I volunteer to be one of her control subjects.

When we sit down in a lab room, LePort gets right down to business. "Tell me everything that happened - all the details that you can remember from today. You have two minutes." That time limit is important when working with HSAMers, says LePort; without it, they can go on reminiscing for quite a while. Now that it's my turn, however, I'm not sure where to begin. "Okay, well, I woke up at the hotel and then called my son back in Texas..." I continue with the minutiae of my day: the hotel's extensive breakfast buffet, the traffic on my way to the lab, before recounting my meeting with LePort and McGaugh.

Then I repeat the exercise for the previous six days, pulling up more dull day-to-day fodder as well as a row with my ex-husband and my son's graduation from kindergarten. I am also asked to rate the uniqueness and emotionality of each day. Soon I am convinced that I have the most boring life in the world.

The next exercise is harder. LePort asks me what I was doing on those same dates a year ago. With the peg of a holiday weekend, I muster up a family barbecue and the sad retiring of a flattering bathing suit. But when she asks me to recall the corresponding week from 10 years ago, I am lost. I know I lived in Atlanta, Georgia, and had just started dating the man who is now my ex-husband, but I cannot retrieve any specific events.

With the HSAMers, says LePort, it's a different story. Her initial findings are that, when asked to describe the events of one day a month back, they can recall just under half of the details they provided when interviewed on the day in question. "But if you compare a month out and then ten years out, the information HSAMers recall is about the same." In other words, whatever they manage to recall a month later is still fresh in their minds a decade on.

LePort is fascinated by what might be going on in the brain over that first month. Her hunch is that HSAMers hold on to the gist of a day and lose some of the incidental details. "It's important to understand that [HSAMers] do forget," says LePort. "It's just that they don't forget as much as you or me." Understanding what types of information they cling on to may help us understand more about how they can remember so much, she says.

One theory concerns emotions. Research on animals and humans has shown that if strong emotions accompany an event, then the details can be seared into memory - a process in which the amygdalae, small almond-shaped structures next to each hippocampus, are involved. McGaugh says HSAMers may differ in the way their brains process emotional arousal. "It's possible that they are operating at such a high level of arousal that all this extra stuff just gets sucked into memory," he says. "But we don't know."

That's a theory that Henner subscribes to. "Since I was a kid, I've tried to fill each day with a certain richness," she says. "Especially since I'm going to remember it no matter what."

Certainly during my own tests, I find that emotion plays a role in my recall. Sadly, I am ineligible to continue as one of LePort's control subjects, because the week for which I recounted my daily memories included a holiday weekend, which could give me an unfair advantage. But one month on, I ask a friend to help me recreate the questioning in my living room, and then check the results against LePort's data. It is quickly apparent that I recall very few of the particulars. What does come back is not the day-to-day routine but the emotional highs and lows - the fight with my ex, and the bittersweet feelings that accompany my son finishing kindergarten. The rest remains elusive.

The emotional arousal theory has been lent credence by a recent paper from a team at Vanderbilt University in Nashville, Tennessee - the only other group to have published work on an HSAMer. An MRI scan revealed that their subject has a right amygdala about 20 per cent larger than normal, as well as heightened connectivity between that side's amygdala and hippocampus (NeurocaseDOI: 10.1080/13554794.2011.654225). "It is possible that the enlarged amygdala is overcharging information somehow, making it more relevant and easier to remember," says neurologist Brandon Ally, who led the work.

But the picture is confused because they only scanned one individual with HSAM, and that person is blind, a fact which could account for the unusual brain anatomy. McGaugh's team has scanned the brains of 11 HSAMers and found their amygdalae were the normal size. Even so, McGaugh notes, this does not disprove the emotional arousal theory: the amygdalae may be unusual in ways that are not visible on the scans.

The scans did reveal interesting details of other areas of the brain, though (Neurobiology of Learning and Memory, vol 98, p 78). To start with, the 11 HSAMers have larger-than-average temporal lobes. That seems to tie in neatly with the fact that these regions are where we store long-term memories, although McGaugh is quick to point out that we can't assume anatomy is cause rather than effect. "We don't know if the way they remember makes changes to the brain, or those changes in brain structure result in the way they remember," he says. There were also differences in the left uncinate fasciculus, a fibrous pathway that connects the hippocampus and amygdala to the frontal cortex and which, when damaged, has been linked to impaired autobiographical memory

More unexpectedly, the caudate nucleus (see diagram) and other areas implicated in obsessive-compulsive disorder (OCD) were also larger than average. Although none of the HSAMers has been diagnosed with the condition, McGaugh says it is compelling that all of them have what he calls "obsessive-like or compulsive-like" behaviour. "We see things like germ avoidance," he says. "If keys are dropped on the floor, they have to be washed before being put back in the pocket. We also see compulsive-like organisation, and that takes many forms."

Although she bristles at the idea of having OCD, Price agrees she is organised. "I'm organised in my head and I'm organised in my life," she tells me. "If you need something, it doesn't matter if it was from 10 years ago - all you have to do is tell me."

LePort thinks that the HSAMers' obsessive tendencies could be important. "It may be that a form of unconscious rehearsal is taking place," she says. Some studies suggest that such rehearsal contributes to the ability to store memories in the long term.

That idea, and the emotional arousal theory, remain hypotheses that need further testing. None of the research so far has shown a convincing way for those of us with ordinary memories to start replicating the HSAMers' abilities. McGaugh thinks most people could do better if they just tried harder. "We can probably do a better job," he says. "But you're not going to improve it to a level that these folks have it."

Over the course of my visit, McGaugh stresses that his research into the mechanisms behind superior memory is just beginning. Price, who originally contacted McGaugh in a quest to understand her extraordinary abilities, is hopeful that an explanation will emerge one day, although she is not holding her breath. "It's been 12 years," she says. "And I'm still waiting."

Kayt Sukel is a science and travel writer based in Texas. She is the author ofDirty Minds: How our brains influence love, sex and relationships

They never forget: The strange gift of perfect memory - 科学松鼠会 - 科学松鼠会
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