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Babies absorb information like a sponge. So why do we struggle to recall our first few years?

WHEN my younger sister was born, I was almost 6. I woke up early the day after Christmas and asked my teenage sister where our parents were. “They’re at the hospital having the baby,” she said. “Go back to bed.”

I remember that conversation clearly, but the actual arrival of my baby sister? Nothing. I don’t recall visiting her in the hospital and holding her tiny pink hand for the first time, or my mother bringing her home and tucking her into her crib in the room next to mine.

There is nothing unusual in the failings of my early memory. In fact, “childhood amnesia”, as the phenomenon is known, is universal. Most people remember nothing from before the age of 2 or 3, and memories from the next few years are sketchy at best.

This is puzzling, because in other ways children are phenomenal learners. In our first couple of years we pick up many complex, lifelong skills, like the ability to walk, talk and recognise people’s faces. Yet memories of specific events in our childhood are lost to us in adult life. It’s as if someone has torn the first few pages from our autobiography.

So what causes childhood amnesia? The question has troubled psychologists for more than a century, but at last we are starting to see some plausible answers. The new findings explain why some of us can remember more of our childhood than others, and even raise the question of whether it might be possible to unlock those earliest memories.

The first serious study of the problem, by the French psychologists V. and C. Henri, was in 1898. The pair found that when adults were asked about their earliest autobiographical memories, the average age at which these events occurred was just over 3 years. These findings have been confirmed by numerous later studies, which point to an average age of between 3 and 3.5 years for the very first memories. Even then, we still have notably poor recall for the following 3 years or so, at which point things start to become clearer. There is a lot of variability, however: some people seem to remember events before age 2, while others recall nothing before 6 or even 8.

Attempts to explain the phenomenon came in fits and starts in the decades after the Henris published their work. Sigmund Freud put his mind to the problem in a 1905 essay, concluding that we repress childhood memories because they are full of sexual and aggressive impulses too shameful for us to face. That idea eventually fell by the wayside, to be replaced by the view that young children just can’t form explicit memories of events.

The picture changed again in the 1980s, with the first studies of children themselves, rather than investigations of adults’ childhood recollections. This revealed that children as young as 2 or 3 can indeed recall autobiographical events, but that these memories fade away. The question therefore became: What causes them to disappear?

There appears to be no simple answer. “We’ve come to this view that there are a number of factors that coalesce to allow us to retain our memories,” says at the University of Otago in Dunedin, New Zealand, who studies how memory abilities change during childhood and adolescence.

One of those factors may be the brain’s anatomy. Two major structures are involved in the creation and storage of autobiographical memories: the prefrontal cortex and the hippocampus. The hippocampus is thought to be where details of an experience are cemented into long-term memory.

Broken bridge

It’s here that the problem seems to lie. “We used to think the hippocampus and the surrounding cortices were well developed early on,” says , who studies the development of memory during childhood at Emory University in Atlanta. But in the past 15 years or so, it has become clear that one small area of this region, called the dentate gyrus, does not fully mature until age 4 or 5. This area acts as a kind of bridge that allows signals from the surrounding structures to reach the rest of the hippocampus, so until the dentate gyrus is up to speed, early experiences may never get locked into long-term storage, Bauer says. “If the route isn’t sufficiently mature to allow the information to get in, it’s not going to effectively consolidate.”

Hayne agrees that the brain continues to mature over a long period of development, and that this is an important step in establishing long-term memories. Yet children can still remember some events before this region is fully developed, so it can’t be the be-all and end-all of childhood amnesia.

What’s more, there are puzzling cross-cultural differences in the age of earliest memories. In one cross-cultural study, for example, researchers found the average age of first memories in people of European descent hovered around 3.5 years, compared with 4.8 years for east Asians and 2.7 years for Maori people in New Zealand ().”Those differences cannot be explained by brain maturation alone,” she says. Clearly, there must be more pieces to the puzzle.

at Lancaster University in the UK thinks he has come across one of the other important factors. “The thing that brings childhood amnesia to an end,” he suggests, “is the advent of what we call a cognitive self.” That’s our sense of our own uniqueness – the understanding that the entity “me” is different from “you”. This ability emerges at around 18 to 24 months of age, just before autobiographical memory begins to surface. Could it be the answer?

Over the past 10 years, Howe has explored this idea through a series of experiments. In one of his recent studies, for example, he tested whether toddlers could recognise themselves in a mirror, a well-accepted sign they have developed a sense of self. Next he showed them a stuffed lion, which he then tucked into one of several drawers in a set of cabinets. Weeks later, he brought each child back to the lab and asked if he or she remembered where the lion was napping. “The children who had a cognitive self at the time of the lion event were able to remember weeks later,” he says, “whereas children who didn’t have a cognitive self did very poorly.”

Howe believes our sense of self helps us to organise our memories, making them easier to recall. “They become more memorable and stay with you for longer periods,” he says. Yet that can’t be the whole story either, since memories continue to be sparse long after the point at which a toddler can recognise his or her reflection. “The cognitive self is a necessary – although maybe not a sufficient – condition for autobiographical memory,” Howe concedes.

The magic shrinking machine

Some other factor is therefore needed to explain why memories continue to be sparse well beyond the point at which our cognitive self appears. For Hayne, the extra ingredient is the development of language skills. To investigate, she asked a group of 2 to 4-year-olds to play with a toy called the “magic shrinking machine”. The kids had to place an object in the machine and perform a series of actions before an identical but smaller version of the object popped out. Hayne also recorded the words the kids could speak and understand at the time they played the game.

Then, six months to a year later, she brought the children back and asked them about the magic shrinking event. They could remember the game and re-enact aspects of it, but in no instance did they use a word to describe the machine that had not been part of their vocabulary when they first played with it – even though their vocabularies had grown by leaps and bounds in the meantime (). “Their ability to describe it was really locked relative to their language at the time of the event,” she says.

Further evidence came last year, when and at the University of Leeds, UK, published a study that again suggested the contents of our first memories depend on our first words. They asked adults to describe and date their earliest memories associated with words like “ball” or “Christmas”. It turned out that the earliest memories around each cue word dated to several months after the average age at which the word is acquired (). “You have to have a word in your vocabulary before you’re able to set down memories for that concept,” Morrison concludes.

Perhaps a sense of self provides a structure around which to organise memories, and language then provides a further kind of memory scaffold, anchoring the details in a format we can call up years later. Morrison suggests that this may be because language allows a child to construct a narrative, which might help them to consolidate their memories. A 2-year-old can identify a dog, for example, but it takes until about 4 before the child can flesh out a story about their new pet. “Is it coincidental that autobiographical memory emerges at the same stage at which a child is able to give you a narrative account of an experience?” Morrison asks.

“Is it coincidental that autobiographical memories emerge at the point a child is able to give a story of their experiences?”

Hayne and her colleagues have explored the importance of narrative by recording conversations between mothers and their children at various points between the child’s second and fourth birthdays, noting whether each conversation included “elaborations” (richly detailed descriptions) or merely “repetitions” (which focus on just one or two aspects of the event). Ten years later, the team contacted the children and asked them about their early memories. This revealed that those whose mothers had many more elaborations than repetitions within their conversations had distinctly earlier memories than children of mothers who had a lower elaboration-to-repetition ratio (). In other words, the way you talk to your kids when they are young might shape what they will remember years down the road.

This could also explain those puzzling differences between cultures. Compared to east Asian parents, European and North American parents tend to discuss the past more often with more elaborate storytelling. As a result, their children have more early memories. The Maori storytelling culture is even richer, with detailed oral histories and a strong focus on the past, leading to even earlier memories. When it comes to autobiographical memory, “early family memory sharing is important”, says at Cornell University in Ithaca, New York, who studies the interaction of cognitive and social development.

Mental time travel

This may seem to confirm that language skills are the key to retaining childhood memories – but in fact the issue is not that clear-cut. Talking about the past doesn’t just help children develop narrative skills, it also fosters development of a sense of self. “In North American culture, people are crazy about memoirs and reality TV. It’s all about life stories,” Wang says, so parent-child conversations in this culture tend to focus on a child’s own experiences and feelings. Among east Asians, by contrast, “the past is the way for us to learn to do better in the future”. Asian parents tend to use past events as teaching tools, and do not dwell on the child’s feelings or role in the event. As a result, children in these different cultures have different understandings of their personal identities.

It now looks as if language and self-perception go hand in hand, and both are necessary for autobiographical memory to flourish. The findings could have a bearing on our wider understanding of the mind. For example, our capacity to plumb the depths of our past appears to be intimately linked to our ability to imagine the future. Given the ways different cultures reflect on their past, you might also expect differences in this “future time travel” – and that’s exactly what Wang has found (). The work might even shed light on the quality of other animals’ memories (see “Memoirs of an elephant”).

One big question remains, however: is it ever possible to reclaim memories from that period of our early childhood that is hidden from us? It is clear that very young children remember a lot in the short term. As many a parent has witnessed, toddlers can accurately describe a trip to the zoo that happened weeks earlier. But such early recollections are fragile and may never become locked into permanent storage. “The likelihood is those early memories are simply not there,” Bauer says.

Hayne’s most recent, currently unpublished, work supports the idea that those early memories aren’t cemented for later retrieval, even if the reminders come soon after the event. She found that the amount of information a 20-year-old remembers about the birth of his 15-year-old brother is virtually identical to the amount of information a 5-year-old remembers about his brother’s birth just a month earlier. “If you plot adult next to child data, they are virtually identical,” she says. She concludes that these memories aren’t simply forgotten as a person ages. “The memory never got in there in the first place,” she says.

Others harbour hopes of being able to recover these early memories, however. “I think they are retained but not accessible,” Conway says. In his view, memories are “snapshots” of sensory experiences. As you mature, you develop language, a sense of self and other conceptual knowledge that helps you to frame those sensory snapshots and access them. If he is right, our buried memories could be excavated – if we could only find the right cues.

That’s a line of reasoning that Morrison also follows. Reaching beyond traditional memory cues of words and images, she is exploring the use of smells, flavours and music for calling up ancient memories. If she and her colleagues can identify the proper tools, perhaps one day I will be able to unearth the memory of meeting my sister for the first time. “One of the things we understand as memory researchers,” Morrison says, “is there’s a lot more in there than we realise.”