New Baby Brain Scans Reveal the Moment We Start Making Memories

A giggling toddler in a pink dress and matching headphones lies down on her back in front of a gigantic whirling machine. A pillowy headrest cushions her head. She seems unfazed as she’s slowly shuttled into the claustrophobic brain scanner.

Once settled, a projection showing kaleidoscope-like animations holds her attention as the magnetic resonance imaging (MRI) machine scans her brain.

The girl is part of a new study seeking to answer a century-old mystery: Why can’t most us remember the first three years of our lives? Dubbed “infantile amnesia” by Sigmund Freud, the study could provide insight into how the brain develops during our early years. And if we can form memories at a young age, are they fleeting, or are they still buried somewhere in the adult brain?

It seems like a simple question, but an answer has eluded scientists.

Though infants and toddlers aren’t yet able to give detailed verbal feedback, studying their behavior has begun to shed light on if and when they remember people, things, or places. Still, the approach can’t peek in on what’s happening in the brain in those early years. MRI can.

A team from Columbia and Yale University scanned the brains of 26 infants and toddlers aged 4 to 25 months as they completed a memory task. They found that at roughly a year old, a part of the brain crucial to memory formation spun into action and began generating neural signals related to things the kids remembered from the tests.

Called the hippocampus, this sea-horse-shaped structure deep inside the brain is crucial to the encoding of our life stories—who, when, where, what. Adults with a damaged hippocampus suffer memory problems. But because wiring inside the hippocampus is still developing during our earliest years, scientists believe it may be too immature to form memories.

“It’s not that we don’t have any memories from that period [infancy],” said study author Nicholas Turk-Browne in a press briefing. “In fact, early life is when we learn our language. It’s when we learn how to walk…learn the names of objects and form social relationships.”

“What happens during that period when we learn so much, but remember so little?” he added.

Stages of Memory

Memory seems like all-or-none: You either remember something, or you don’t.

It’s not that simple. Decades of research have identified the hippocampus as the main orchestrator of episodic memories. These allow you to remember an acquaintance at a party, where you parked your car, or what you had for dinner three nights ago.

Each everyday experience is encoded in neural connections in the hippocampus. Groups of neurons called engrams capture different memories and keep them separate, so that they don’t bleed into each other.

Once encoded, the brain etches important memories into long-term storage during sleep. Studies of slumbering rodents and humans after learning a new task found that the hippocampus replayed brain activity at higher speed during the night, correlating with better performance on a trained memory task the next day.

The last step is retrieval. This is when the brain fishes out stored memories and delivers them to our conscious brain—and so, we “remember.”

Failure of any of these steps causes amnesia. So, which steps are responsible for the erosion of baby memories?

Bundles of Joy

Brain scans from 26 infants now offer some intriguing clues.

The team behind the new study scanned the children’s brains with functional MRI (fMRI) as they looked at a screen in the scanner and took a memory test. fMRI captures brain oxygen levels (BOLD) as a proxy for local neuron signaling—higher levels mean more brain activity.

The head needs to keep very still throughout the scans to avoid blurring. That’s not easily accomplished with babies and toddlers. Previous studies circumvented the problem by imaging their brains while sleeping, but the results couldn’t capture memory processes.

To keep the infants happy, engaged, and safe, parents brought favorite blankets and pacifiers, and younger infants were wrapped inside a comfortable vacuum pillow to reduce movement. A video system projected images onto the ceiling of the scanner within their line of sight.

As the kids looked at a bright kaleidoscope-like video, images of faces, scenes, and objects would flash for a few seconds. These included toys or landscapes of an alpine cabin with mountains in the background. Previous studies found infants like to stare at objects or images they’ve seen before compared to new objects, suggesting they remember previous encounters.

Throughout the sessions the team added projections showing a previously seen picture and a new one and monitored the infants’ eye movement using a video camera.

“The ingenuity of their experimental approach should not be understated,” wrote Adam Ramsaran and Paul Frankland at the Hospital for Sick Children in Toronto, Canada, who were not involved in the study.

BOLD Findings

The kids often squirmed during the sessions. Some weren’t interested in the pictures; others fell asleep in the scanner.

Still, the team managed to capture hippocampal BOLD signals averaging roughly eight minutes per participant and matched them to memory performance. On average, parts of the hippocampus ramped up activity for images that the infants later remembered—that is, they looked at it for longer during the test phases.

But not all infants performed the same. The younger cohort, under a year, didn’t show the surge of BOLD signals suggesting memory encoding. They also ignored already seen images compared to new ones.

It seems babies start encoding memories around a year of age, even as their hippocampus is still developing.

The results are similar to those in baby rodents. The early years are chaotic. The brain undergoes extensive rewiring. This makes it a difficult to form lasting memories. Yet some supposedly lost memories encoded at a young age can be recovered later in life with reminder cues or by directly activating the set of neurons that originally encoded the memory.

That’s not to say infants can acquire rich recollections—stories including multiple people, places, and things—at a year. The study only tested brain signatures for individual components.

Future studies tracking the hippocampus might shed light on the minimal brain architecture needed to support vivid autobiographical memories. Examining other stages of memory could shine more light on infantile amnesia. For example, do infants also replay neural signals as they sleep to etch new experiences into long-term memory?

And maybe—just maybe—our earliest memories could one day be retrieved later in childhood or beyond.

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