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Just How Much Will Toddlers Remember? The science of memory

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When I told my four-year-old about our upcoming plans to spend a week swimming, fishing, and barbecuing at a lake house, his response baffled me: “Will the big Bobcat tractor be there?” he asked. He was referring to a trip we took over Thanksgiving to the same house — when he was only one and a half.

The idea that my preschool-aged son has a vacation memory of himself toddling around in diapers is fascinating. I’m continually amazed at his brain’s tape recorder-like capacity. But there’s a twist to the story of childhood memory, one that intrigues parents and researchers alike: although that early lake house fun is crisp for my son now, when he reaches middle childhood, it will be gone. Not only that, the memory of this summer’s upcoming trip may be lost along with it.

Why do we forget our early years? And how can this time in our children’s lives be so important when they won’t remember much of it at all?

Most adults can conjure up memories from preschool. Yes, some of us swear we remember our cribs, while others say they’ve blanked on everything until school age, but researchers more or less agree that adults’ earliest memories date back to age three or four. We have a dense amnesia for the first few years of life, and then a period of relatively sparse memories for a few years after that.

The reason we can’t access our early days is a source of debate, and there seems to be not one, but multiple explanations. For example, some psychologists say that for memories to be properly coded long term, a child needs advanced language skills to both store and retrieve her experiences. If you ask a 20-year-old to remember a family trip she took at age two, you’re both using language to pose the question, and asking her to recount the memory back to you in spoken words. Both of these could be a challenge, since she didn’t have language back when the event occurred. And it’s true that memories do seem to stick around the time when fluent language develops.

Another possible explanation for childhood amnesia is that memories develop alongside a child’s self-concept. Little children take time to grasp the idea of themselves as separate beings. The true notion of “me-ness”— being a person with her own thoughts and feelings independent from others — is a work in progress in toddlerhood. Many argue that you can’t log experiences into an autobiographical memory system until you’re able to fully see yourself as a distinct individual.

Of course there’s the simple fact that little brains are still immature, and it’s possible that the machinery needed to code memories, or transfer them from short- to long-term, simply doesn’t exist until later years. The hippocampus — a curved ridge deep in the brain — is central to forming lasting memories. Scientists think that as it matures and strengthens connections to the rest of the brain through childhood, memory storage improves. We know how important the hippocampus is to memory in part because of the famous patient H.M.

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In 1953, H.M. had a section of his brain removed (later found to include the hippocampus) to cure a seizure disorder. The surgery worked, but from that point until his death 55 years later, H.M. couldn’t remember anything for more than about 20 seconds. He could recall life up to the point of the procedure, but beyond that day and until his death at age 82, his autobiographical memory wiped itself clean with each passing moment.

I’ve spoken to researcher Carolyn Rovee-Collier about this idea that babies and little kids can’t code long-term memories. Rovee-Collier has been testing young subjects for decades and believes we misunderstand infant memory. Her studies show that even the smallest babies have impressive recall under certain conditions. In one of her experiments, a baby is placed under a mobile with a string attaching it to her foot. When she kicks, the mobile moves. Infants learn this quickly and start to kick furiously for entertainment. Time passes, and the researchers place the baby under the mobile again without attaching the foot. If a baby remembers the earlier session, she will kick immediately. At first, Rovee-Collier found that two-month-olds remember for a day or two, six-month-olds for about two weeks, and nine-month-olds for a month and a half — in fact this is what I reported years ago for a Babble piece on the limitations of kids’ memory. But more recently, she discovered that if babies are periodically reminded of the mobile (just shown it, not allowed to touch or re-learn the experiment) and then re-tested, a two-month-old will remember through seven months of age, and a six-month-old past the age of two.

This is a perplexing fact about childhood amnesia. Babies, toddlers, and preschoolers actually do have robust memories — even long-term ones. As a parent you’ve no doubt seen this in action, as I have. Once when we visited my dad’s house and my son was two-and-a-half, he beelined immediately to the broom closet because he remembered, from another trip a full year before, that it contained his favorite plaything.

It’s clear that little kids are far from being amnesiacs like H.M., but how far back a person can remember seems to depend on how old he or she is when you ask. Researcher Karen Tustin discovered this a few years ago when she found that the earliest memories we retain as adults average from age three-and-a-half, but children and even adolescents can remember events from before they turned two. Similarly, Canadian researcher Carole Peterson reported last year that while younger kids have quite early memories, those memories often fade two years later. In a recent New York Times article, she summed it up by saying, “This age of earliest memory seems to be a moving target.”

So while my four-year-old may surprise me with his lake house recollections from toddlerhood, when he’s a teenager and I ask him about it, he will look at me with a blank stare. Even this upcoming summer vacation — with all its magical swimming adventures, exciting bug hunts, and quality family time over puzzles and games — could have limited real estate in his brain once he gets to elementary school.

That’s a fact that sometimes makes me sad, since I cherish his company and our time together so dearly. But remember that conscious, autobiographical (also known as “explicit”) memories are only the tip of the iceberg. “Implicit,” or unconscious, recollections shape us too. The truly important and formative memories are the ones we don’t have words for — the ones that are logged somewhere deep in our children’s brains. That’s where our kids learn that they are loved, that relationships bring them joy, and that people can be trusted. No, my son probably won’t always remember the time when we barbequed on the grass, my husband wrapped his own sweatshirt around him like a cape, and we all laughed. But what he will remember is that his favorite people always take care of him, relationships are intimate and fun, and life is good.

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