Babies may be good at remembering, and forgetting
In one of my earliest memories, I’m wiggling around on the kitchen floor of my childhood home. My mom had just dropped a bunch of oranges for my brother and me to bang around, maybe to loosen them up for juicing. We scramble and grab the oranges, throwing them against the floor with glee. I don’t know how old I was at the time, but I’d guess I was between 3 and 4.
As Baby V charges through her second year of life, I often wonder if she’s going to remember any such twinkling moments. Will she remember her intense joy at seeing the garbage truck roll by every Friday morning? Will she remember the trauma of having her teeth brushed?
I won’t know, of course, at least not until she’s old enough for me to ask her. Although scientists have long been fascinated with how the brain forms memories, they’ve paid less attention to how those memory-storing brain systems first emerge.
Nobody knows exactly why babies spend much of their time in a foggy state of “infantile amnesia.” Recent work from mice hints that a flurry of newborn nerve cells in the brain’s hippocampus might interfere with early memories. Other research suggests that in young babies, key memory areas in the brain aren’t yet fully connected to other regions.
Reasons for this temporary amnesia aside, the good news is that it eventually disappears. The consensus, from both people’s personal experiences and a handful of studies, seems to be that children start forming long-lasting memories around 3 1/2 years old.
As with any average, subtle differences hide in that number. Women seem to remember events that happened slightly earlier in their lives than men. Cultural differences may exist too: New Zealand Maori adults can reach back further into their early lives than those of European or Asian ethnicity, one study found.
Most of these studies asked adults to recount their earliest memories. Now, some researchers are starting to think that the problem might not be a matter of memory formation, but one of remembering. And one of the ways to test this idea is to ask people about their earliest memory before they forget. In other words, ask a kid.
When scientists have done that, they found that earliest memories get even earlier. Children are able to call up memories, verified independently by their parents, from their very early lives, a study published in 2010 in Developmental Psychology suggests. In that study, over 20 percent of 5-year-olds and 8- to 9-year olds recounted events from their first year, some from the very first months of life.
Combined with data from lab experiments, those results suggest that very young babies are actually quite good at forming memories, Sinéad Mullally of Newcastle University and Eleanor Maguire of University College London write in the July Developmental Cognitive Neuroscience.
And there’s more evidence that babies’ and young children’s brains can encode information just fine, but aren’t able to recall it later. In a recent study, 3-year-olds were good at remembering something for about 15 minutes, but not over the course of 24 hours. In the test, children were shown a locked pirate’s treasure chest in a sandbox. Alas, no key was in sight. When choosing between three objects 15 minutes later, the 3-year-olds were more likely to pick the key, remembering that it could be used to unlock treasure. But by a full day later, the kids had forgotten that the key would come in handy, and weren’t more likely to choose the key over the other objects. Four-year-olds, on the other hand, still chose the key a full day after encountering the locked treasure chest.
In their review, Mullally and Maguire write that brain imaging techniques might be helpful in sorting out how the brain begins to remember. Certain imaging methods might ultimately allow scientists to watch a memory stick around or disappear as a child grows up. New windows into the growing mind may reveal some surprises in our earliest lives.
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