Have you ever wondered why you can’t remember being a baby? Your first words? What about your first steps? Don’t worry, you’re not alone. Psychologists have a special term for the fact that most adults can’t remember much about their early lives, typically up to age 3-4. They call this phenomenon childhood amnesia.
Why do we lose these early memories? Is it because babies can’t form them in the first place, or is something else at play? Turns out that baby humans aren’t the equivalent of a cute blob of goldfish.
Using brain scans of awake infants, researchers have found that the hippocampus — a seahorse-shaped region of the brain that is involved in memory — begins to encode individual experiences as early as one year of age. This challenges a long-held belief that infantile amnesia is due to an immature hippocampus incapable of forming memories. Instead, it suggests that the memories are there, but they become inaccessible as we grow older.
“One really cool possibility is that the memories are actually still there in adulthood. It’s just that we’re not able to access them,” study co-author Tristan Yates, a neuroscientist at Columbia University in New York City, told Nature.
The Mystery of Infantile Amnesia
Even though babies are constantly learning, their memories of specific events seem to vanish. For years, scientists thought this was because the hippocampus, which plays a key role in forming and retrieving memories, wasn’t mature enough to do its job in infancy.
But evidence from animal studies hinted that this might not be the whole story. In rodents, for example, the hippocampus can form memories during infancy, but those memories become inaccessible without direct stimulation. Could the same be true for humans?
To find out, a team of researchers led by Yates, who during this study was a graduate student at Yale University, turned to functional magnetic resonance imaging (fMRI). They scanned the brains of 26 infants, ranging from 4 to 24 months old, while the babies viewed a series of photographs. The researchers then tested the infants’ memory by showing them pairs of images — one they had seen before and one that was new — and tracked where the babies looked. If babies stared longer at an image they had seen before, it signaled recognition.
In infants older than 12 months, the hippocampus showed significantly more activity when they viewed images they recognized. This “subsequent memory effect” was particularly strong in the posterior hippocampus, a subregion that plays a role in encoding detailed, episodic memories in adults.
“The hallmark of these types of memories, which we call episodic memories, is that you can describe them to others, but that’s off the table when you’re dealing with pre-verbal infants,” said Nick Turk-Browne, a professor of psychology at Yale and senior author of the study.
Statistical Learning
Previously, Turk-Browne found that infants as young as three months old can engage in “statistical learning,” a type of memory that involves extracting patterns from repeated experiences. For example, a baby might learn the typical sequence of events during mealtime or recognize common features of faces. It’s the same mechanism that scientists think is behind some dogs’ ability to memorize and respond to words and phrases. This form of memory relies on the anterior hippocampus, which develops earlier than the posterior region responsible for episodic memory.
“Statistical learning is about extracting the structure in the world around us,” Turk-Browne explained. “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.”
The new findings suggest that episodic memory emerges later, around the one-year mark, as the posterior hippocampus matures. But if infants can form these memories, why don’t we remember them as adults?
One explanation is that early memories simply fade over time, never making it into long-term storage. Another explanation says that these memories actually persist somewhere in our psyche but become inaccessible. It’s like having a book in a library but losing the card that tells you where to find it. Turk-Browne leans toward the latter, citing recent animal studies.
Can We Get Them Back?
In mice, for example, researchers have shown that early memories can be retrieved by reactivating specific hippocampal neurons, even after they seem to have been forgotten.
“Although mice who learn the location of an escape hole in a water maze during infancy forget this location by maturity, optogenetic reactivation of the hippocampal neurons that were activated during encoding can elicit the learned behavior,” the researchers said.
This is what they’re studying now. In ongoing experiments, they are testing whether children can recall home videos taken from their perspective as babies. Preliminary results suggest these memories might persist until preschool age before fading — a finding that could reshape our understanding of memory development.
This could also have practical implications. If we can better understand how and why early memories are lost, we might be able to develop interventions to help children with memory impairments or those who have experienced trauma.
So, while the memories of our first years may remain elusive, they are far from forgotten — just hidden, perhaps, in the intricate folds of the developing brain.
The findings appeared in the journal Science.
