Why is it difficult to recall memories from the first year of life?

Challenging assumptions about infant memory, a new Yale-led study shows that 12-month-old young infants can code memory. Findings suggest that infant amnesia – the inability to remember the first few years of our lives – is likely caused by impaired memory retrieval, rather than being unable to form memories in the first place.

Despite childhood being a period of rapid learning, memories from this point do not continue to later childhoods or adults.

In general, humans cannot remember events in the first three years of their lives. This is a phenomenon known as infant amnesia.

The reason why grown-up humans have long-standing blind spots in their episode memories during their early childhood remains the puzzle.

One theory suggests that this occurs. This is because the hippocampus, a brain region important for episodic memory, is not fully developed during infancy.

However, rodent studies challenge this idea that memory traces or sculptures are formed in the infant hippocampus, but are inaccessible over time.

In humans, infants exhibit memory through behaviors such as conditioned responses, mimicking, and recognition of familiar stimuli.

However, it remains unclear whether these abilities are dependent on the hippocampus or other brain structures.

“The characteristic of these types of memories we call episode memories is that you can explain them to others, but that’s off the table when you’re dealing with pre-language toddlers.”

For this study, researchers wanted to identify robust methods for testing temporary memory in infants.

Scientists used an approach that showed images of new faces, objects, or scenes in infants between four months and two years.

After that, after the infant saw several other images, they showed the previously seen images next to the new one.

“When the baby sees something previously, when they see it again, they’re hoping to see more of it,” Professor Torque Brown said.

“In this task, if the toddler is staring at a previously seen image more than the new one next to it, it can be interpreted as the baby perceives it as familiar.”

The authors have pioneered methods for performing functional magnetic resonance imaging (fMRI) with awake infants over the past decade (has been historically difficult due to the short attention span and inability to remain stationary).

Specifically, we assessed whether hippocampal activity is related to infant memory strength.

They discovered that the greater hippocampal activity when infants are looking at new images, the longer they see it when the infant reappears later.

The posterior part of the hippocampus (near the back of the head) where encoding activity was most intense, is the same region that is most associated with adult episodic memory.

These findings were true across a sample of 26 infants, but were the strongest among infants over 12 months (half of the sample group).

“This age effect leads to a more complete theory of how the hippocampus develops to support learning and memory,” Professor Torque Brown said.

Previously, the team found that the hippocampus of a 3 month-old young infant exhibits a different type of memory known as statistical learning.

While the memory of the episode deals with certain events, such as sharing Thai meals with out-of-town visitors last night, statistical learning is to extract patterns across events, such as restaurants that look like restaurants, specific dishes found or typical appearances where they are served seated.

These two types of memory use different neuronal pathways in the hippocampus.

And in previous animal studies, researchers have shown that statistical learning pathways seen in the anterior part of the hippocampus develop faster than that of temporary memory.

Therefore, the authors suspected that episodic memories could appear in childhood for about a year or more.

This developmental progression makes sense when thinking about the needs of babies.

“Statistical learning is about extracting the structure of the world around us,” Professor Torque Brown said.

“This is important for the development of language, vision, concepts, etc., and so I understand why statistical learning is played faster than episodic memory.”

Still, new research shows that episode memories can be encoded by the hippocampus earlier than previously thought, long before the earliest memories that can be reported as adults. So what about these memories?

“There are a few possibilities,” Professor Torque Brown said.

“One thing is that it simply doesn’t last long because memory may not be converted into long-term storage.”

“The other thing is that memories are still there long after encoding and we don’t have access to them.”

“And we think that might be the latter.”

“In our ongoing work, we test whether toddlers, toddlers and children remember home videos taken from the perspective of (young) babies.

“The new findings provide important connections.”

“Human work is significantly compatible with recent animal evidence that infant amnesia is a problem of recovery.”

“We are beginning to track the durability of hippocampal memory throughout childhood and entertain the possibilities of radical science fiction.

study Published in the journal Science.

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Tristan S. Yates et al. 2025. Hippocampal encoding of human infant memory. Science 387 (6740): 1316-1320; doi: 10.1126/science.adt7570