Scientists have discovered why we don’t remember being a baby, despite learning so much in those early years of life.
Researchers have long believed we don’t hold onto these experiences because the part of the brain responsible for saving memories — the hippocampus — is still developing well into adolescence and just can’t encode memories in our earliest years.
But now researchers at Yale have found this is not the case, and suggest we just can’t access them.
For the study, published in the journal Science, researchers showed 26 infants aged four months to two years an image of a new face, object, or scene and later tested whether they remembered them.
The infants were then shown several other images before being shown a previously seen image next to a new one.
“When babies have seen something just once before, we expect them to look at it more when they see it again,” said Professor Nick Turk-Browne, senior author of the study.
“If an infant stares at the previously seen image more than the new one next to it, that can be interpreted as the baby recognising it as familiar.”
Researchers took brain scans using functional magnetic resonance imaging (fMRI) to measure activity in the infants’ hippocampus while they viewed the images.
They found that the greater the activity in the hippocampus when an infant was looking at a new image, the longer the infant looked at it when it reappeared later.
Although this was the case for all the infants, those older than 12 months showed the strongest brain activity, suggesting the hippocampus develops to support learning and memory.
Previous research by the team at Yale found infants as young as three months old displayed a type of memory called “statistical learning.”
While episodic memory deals with specific events, statistical learning is about extracting patterns across events, such as what a place looks like.
Professor Turk-Browne said he suspected that episodic memory may appear later in infancy, around one year or older. He argued that this developmental progression makes sense when thinking about the needs of infants.
“Statistical learning is about extracting the structure in the world around us,” he said. “This is critical for the development of language, vision, concepts, and more. So, it’s understandable why statistical learning may come into play earlier than episodic memory.”
However, this latest study shows that episodic memories can be encoded by the hippocampus earlier than previously thought, long before the earliest memories we can report as adults. This raises questions about what happens to those memories.
One possibility, according to Professor Turk-Browne, is that is that the memories may not be converted into long-term storage.
However, he has theorised that memories are still there long after encoding and we just can’t access them.
In ongoing work, Professor Turk-Browne’s team is testing whether infants, toddlers, and children can remember home videos taken from their perspective as babies, with tentative pilot results showing that these memories might persist until preschool age before fading.
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