被遗忘的童年――为什么以前的记忆会逐渐消失Mellissa Block （Host）：Memories are a big part of our identities. Recalling our experiences helps us know who we are. Yet there are some events we can’t recall even though they may have helped shape our lives. These are things that occurred in the first three or four years of life.Jon Hamilton：Francis Csedrik just turned eight and lives in Washington D.C. Like most kids，he remembers lots of important events in his life so far. There was the time he got a 1）concussion.Francis Csedrik：I fell，head first，on a marble floor.Hamilton：The day he watched the family car get stolen.Francis：And my dad had to chase it down the block.Hamilton：Then there was the morning he encountered an unexpected visitor.Francis：A black bat sleeping right above our door.Joanne Csedrik：The bat，oh，you remember that.Hamilton：That’s Francis’s mom，Joanne Csedrik. She’s been asking her son about things that happened to him when he was four，or almost four. Then she asks him about an earlierevent that took place when he was just three，a family trip to the Philippines.Joanne：It was to celebrate someone’s birthday.Francis：Mm-mm.Joanne：You don’t remember？We took a long plane ride，two boat trips.Francis：No，I don’t remember.Hamilton：That’s not surprising. Patricia Bauer of Emory University says by the time most kids are seven or eight，they have started losing some of their early memories. And she says experiences will continue to disappear over the next few years.Patricia Bauer：Most adults do not have memories of their lives for the first three to three and a half years.Hamilton：Bauer says scientists once thought childhood amnesia occurred because the brains of young children simply couldn’t form lasting memories of events. Then in the 1980s，she and other researchers began testing the memories of children as young as nine months old，using gestures and objects instead of words.Bauer：And what we found was that even as young as the second year of life，children had very 2）robust memories for these specific past events.Hamilton：And that raised a question：If children can remember what happened in their early years...Bauer：Why is it that as adults we have difficulty remembering that period of our lives？Hamilton：Bauer says the evidence suggests that children are somehow losing access to their early memories. She wanted to know when this was happening. So she studied a group of children to see what happened to their memories over time. At age three，she says，the kids were recorded speaking with a parent about recent events. Bauer：They tended to be just everyday family activities，visiting an amusement park，a picnic，a visit from a relative.Hamilton：Then as the kids got older，Bauer and her colleagues checked to see how much they remembered. She says children as old as seven could still recall most of the events.Bauer：In contrast，the children who were eight and nine years of age，those children recalled fewer than 40% of the events. And so what we observed was actually the 3）onset of childhood 4）amnesia.Hamilton：Francis Csedrik，who just turned eight，is right at the age when many childhood memories are fading.Joanne：Do you remember celebrating your grandfather’s birthday in the Philippines？Francis：Lolo Santo？Joanne：No，not his birthday.Hamilton：Joanne Csedrik says her son has clear memories of two more recent trips to the Philippines. But the one when he was three is gone. It’s not entirely clear why early memories are so 5）fragile. Bauer says it probably has to do with the structures and 6）circuits in the brain that store events for future recall.Bauer：The brain systems that are responsible for forming memories at the age of three，three and a half，are still relatively immature. It doesn’t mean they’re not working at all，they certainly are. But they’re not working as efficiently and therefore not as effectively as they’re going to be working in later childhood and certainly in adulthood.Hamilton：By the time children are seven or so，their brains are forming memories that are as robust as those formed by adults. Of course，some types of early memories are more likely than others to survive childhood amnesia. Carole Peterson，at Memorial University in Newfoundland，Canada，says one example is memories that carry a lot of emotion. She showed this in a study of children who’d been to a hospitalemergency room when they were as young as two.Carole Peterson：They had broken bones. They were 7）lacerated，had to be 8）stitched up. Things like that. So these were very emotional，very significant events. And what we have found is that even 10 years later，children have enormously good memory of them.Hamilton：Francis Csedrik certainly remembers the events that led to his emergency room visit.Francis：My friend Asher，he said：I want to carry you down the stairs. I didn’t want him to but he didn’t listen. He did it. And I fell，head first，on a marble floor. Hamilton：Researchers say a person’s life story usually includes at least some events that had been lost to childhood amnesia. That’s because when our own memories fail，we rely on family members，photo albums，and videos to fill in the blanks.梅丽莎?布洛克（主持人）：回忆是我们身份的一个重要组成部分。