Imma Perfetto
Cosmos science journalist
A fascinating piece of research might have revealed that our brains are memorising the earliest times of our lives, but the memories have been packed away and just can’t be accessed.
The inability to remember our first few years of life, a phenomenon termed “infantile amnesia” by psychologist Sigmund Freud, has fascinated neuroscientists for more than a century. But we still don’t know why this years-long blind spot occurs.
Studying squirming, pre-verbal babies isn’t easy, but a team from Yale University in the US has been able to make some headway.
Scientists have long thought that the inability to recall our baby days could be because the hippocampus – the part of the brain responsible for saving memories – can’t encode those memories because it’s still developing.
But the authors write in a new paper in Science that infantile amnesia is more likely caused by a failure to retrieve the memories, rather than an inability to form them in the first place.
According to a related perspective, the findings provide “…evidence that the infant hippocampus (a brain region important for memory) can encode the types of information that are required for episodic memory, that is, memories for specific life events containing information about people, places, and things.”
Nick Turk-Browne, professor of psychology at Yale University and senior author of the paper, says that the hallmark of these types of memories is that that you can describe them to others.
“But that’s off the table when you’re dealing with pre-verbal infants.”
Turk-Browne and his colleagues showed 26 infants, aged 4 months to 2 years, an image of a new face, object, or scene. Later, after the infants had seen several other images, the researchers showed them an already encountered image next to an entirely new one.
“When babies have seen something just once before, we expect them to look at it more when they see it again,” says 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 recognising it as familiar.”
The team simultaneously used functional magnetic resonance imaging (fMRI) to measure activity in the infants’ hippocampus while they viewed the images.
“The ingenuity of their experimental approach should not be understated,” writes Adam Ramsaran and Paul Frankland from The Hospital for Sick Children, University of Toronto, Canada, in the related perspective.
In what must be an understatement which will be understood by all parents, Ramsaran says: “Acquiring sufficient fMRI data from awake infants – who cannot be instructed to stay still in a scanner – remains a challenge.”
But the results indicated that, if an infant’s hippocampus was more active upon seeing an image for the first time, they were more likely to appear to recognise that image (looking at it for a longer period) later.
The brain activity was strongest in the posterior region of the hippocampus.
“This is the region of the hippocampus associated with episodic memory in adults, and therefore these data further support the idea that the hippocampus plays a role in memory encoding during infancy,” write Ramsaran and Frankland.
And, while these findings occurred in all 26 infants, they were strongest amongst those older than 12 months.
The 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. So, what happens to them?
There are a few possibilities, says Turk-Browne. One is that the memories may not be converted into long-term storage and thus simply don’t last long. Another is that the memories are still there long after encoding and we just can’t access them.
He suspects it may be the latter.
“We’re working to track the durability of hippocampal memories across childhood and even beginning to entertain the radical, almost sci-fi possibility that they may endure in some form into adulthood, despite being inaccessible,” says Turk-Browne.
His team is now testing whether infants, toddlers, and children can remember home videos taken from their perspective as younger babies.
