Why can’t we remember our early childhoods?
Babies may be able to encode memories in the brain, but cannot access them later
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When asked to recall a first memory, most of us will describe a vivid event from age 3 or 4, such as the first day of preschool or the birth of a sibling. But in general, owing to “infantile amnesia” we have no memory of earlier experiences, such as learning to walk or eating our first solid foods.
Despite being studied for well over a century — the phenomenon was first described by psychologist Caroline Miles in 1893 and further examined by Sigmund Freud in 1905 — infantile amnesia remains largely a mystery.
“It’s relatively rare for people to report memories of events from before they were three years old. That holds no matter whether you ask adults at age 20 or 70,” says Nick Turk-Browne, Professor of Psychology and Director of the Wu Tsai Institute at Yale University. “So, it’s not just forgetting or the passage of time — there’s something missing, memory-wise, from the first few years of life.”
Why do we have infantile amnesia?
A recent study by Turk-Browne and his colleagues suggests it’s an issue not with making memories, but with accessing them. When we make what are known as episodic memories, the details of an experience are converted into a form that can be stored in the brain, or “encoded.” One leading hypothesis is that an immature brain is simply unable to execute this first stage of memory formation. However, the new findings demonstrate that babies can in fact encode episodic memories from around 1 year of age.
Not until age 4 or 5 can a child complete a complicated memory task, Turk-Browne says. “But using more indirect measures of what’s happening in the brain, we see much earlier evidence for advanced cognition than you might expect.”
The hippocampus is a part of the brain that is critical for memory formation. It continues to develop until adolescence. This is the brain region that was thought to be too immature to encode episodic memories until age 3 or later. However, no previous studies had tested for hippocampal memory in babies.
To do so, a team in Turk-Browne’s lab lead by graduate student Tristan Yates tested 26 infants aged 4 to 25 months using a functional magnetic resonance imaging (fMRI) scanner. Adapting fMRI to measure the brains of such young children was no small feat, as their heads must remain motionless for the researchers to obtain usable data. The researchers spent almost a decade coming up with ways to keep infants happy, engaged, and still while in the scanner.
“The researchers spent almost a decade coming up with ways to keep infants happy, engaged, and still while in the scanner.”
“There’s a reason why nobody had done this research before — it’s extraordinarily difficult,” says Turk-Browne. “But the way to make it work is to involve the parents in making sure the baby is as comfortable as possible, and to have them bring things into the machine, like a pacifier, bottle, or blankie.”
The babies performed a fun memory task. During the first part, they were shown individual photographs of faces, toys, or scenes. After a delay, each of these pictures was paired with a second, unfamiliar photograph to determine whether the children could recall seeing the familiar one before. Because many of the infants couldn’t talk yet or follow instructions, Yates and colleagues determined whether they remembered the familiar picture by measuring whether they looked at it longer than the unfamiliar one.
There was more brain activity in the hippocampus when infants were first shown a picture that they would later stare at longer. This indicates that they were encoding the picture in their memory and remembering it. Also, brain activity was most elevated in the posterior hippocampus — the same part of the hippocampus adults use to process episodic memories. This was true in the case of all 26 infants, but was stronger among those older than 12 months.
The findings support a competing explanation of infantile amnesia, which is that babies are storing episodic memories but these memories can’t be accessed in older childhood or adulthood. In other words, the inability to recall our earliest memories could suggest a failure to retrieve rather than a failure to store.
“The inability to recall our earliest memories could suggest a failure to retrieve rather than a failure to store.”
Now, the researchers are exploring other questions about childhood memory, such as how durable infant memories are and why they can’t be accessed later in life.
“I don’t know that our work has any strong translational or practical benefit, other than demonstrating that, although we ourselves don’t remember that period, babies at least around a year old are starting to form memories and retaining things that they experience,” says Turk-Browne. “It does suggest that we’ve underestimated the cognitive capabilities of infants for a long time.”
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