Between getting squeezed through a tube so tight it literally squidges your skull into a weird shape, having teeth force themselves out of your gums at random intervals, and, let’s face it, pooping and peeing yourself near-constantly, it’s probably a kindness, really, that we can’t remember life as a baby. But why we enjoy that little piece of luck has so far been misunderstood, according to a new study – and as it turns out, babies aren’t as forgetful as we thought.
Infantile amnesia, as the phenomenon of forgetting life before the age of three or four is technically known, is a difficult thing to study. The reason why is obvious: babies, famously, aren’t great talkers.
“The hallmark of these types of memories, which we call episodic memories, is that you can describe them to others,” explained Nick Turk-Browne, professor of psychology in Yale’s Faculty of Arts and Sciences and senior author of the study, in a statement this week. “But that’s off the table when you’re dealing with pre-verbal infants.”
Evidently, a different approach was needed – one that played to the babies’ strengths, such as lying down and looking at stuff.
“We investigated the mechanistic basis of this infantile amnesia by scanning the brains of awake infants with functional magnetic resonance imaging while they performed a subsequent memory task,” the paper reports. That may sound like a big ask for a small baby, but rest assured: this “memory task” consisted only of looking at a few pictures and noticing that one of them was a repeat.
If the babies recognized the duplicate, the team should have been able to tell: “When babies have seen something just once before, we expect them to look at it more when they see it again,” said Turk-Browne. “So in this task, if an infant stares at the previously seen image more than the new one next to it, that can be interpreted as the baby recognizing it as familiar.”
But what would happen inside their little heads? Until now, the prevailing wisdom had been that babies can’t form episodic memories because the part of the brain responsible for doing so – the hippocampus – isn’t developed enough yet. It was a reasonable hypothesis, but confirming or disproving it wasn’t really possible (babies, along with being not great talkers, are also not great at staying still for long periods of time, following directions, or paying attention).
That barrier, though, has been gradually broken down over the past decade – and now, the team were able to actually measure the babies’ hippocampal activity throughout the task. What they found ran completely counter to what was previously assumed about infant brains: the longer a baby looked at a familiar image, the stronger the activity observed in their hippocampus.
Not only that, but it was specifically happening in the area associated with episodic memory in adults – a result which “suggest[s] that the capacity to encode individual memories comes online during infancy,” the team writes. While the effect was noticeably stronger in infants over the age of 1 year – accounting for half of the 26-strong sample – it was present in all of them, implying that episodic memories can be formed well before the 3 or 4 years we used to assume.
Of course, this leads to a natural question: if our brains are making these memories, then where do they go?
Well, we’re not sure – and neither are Turk-Browne and his colleagues. But they have a few ideas. Perhaps the memories are created, but only stored short-term; perhaps, as the team’s ongoing research is tentatively hinting, the memories are still there, but locked away somehow, inaccessible to our adult brains. Basically, it looks like “infantile amnesia is a retrieval problem,” Turk-Browne explained.
“We’re working to track the durability of hippocampal memories across childhood,” he said, “and even beginning to entertain the radical, almost sci-fi possibility that they may endure in some form into adulthood, despite being inaccessible.”
The study is published in Science.
