If only we could remember… Hashir Abdulla/EyeEm/Getty

You probably can’t remember life as a 2-year-old. But memory traces from our earliest years might stay in our brains, ready to be reactivated with the right trigger, according to research in rats.

Most people can’t remember the first two or three years of their life, says Alessio Travaglia at New York University. “Some people might say they remember things from this period, but these memories are often inaccurate, or based on stories other people have told them.”

We remember other things from those early years, however. It’s a crucial time for learning, in fact – we start to figure out how to move and communicate, and what we like and dislike, for example. So why don’t our first autobiographical memories stay with us in the same way?


Some have argued that the incredible growth of new neurons during early childhood in brain areas involved in memory formation interferes with the storage of memories, meaning they are lost forever.

Infantile amnesia

To investigate, Travaglia and his colleagues turned to rats, who they believe also experience infantile amnesia. Young, 17-day-old rats – equivalent to a 2 to 3-year-old child – could learn to associate one side of a box with a shock, but the memory would be gone within a day. Older rats could hold onto these memories for several days.

However, the team discovered that the right reminder would prompt young rats’ lost memories to resurface. Once the pups had forgotten to associate one side of the box with a shock, Travaglia and his colleagues gave them another shock. “Suddenly they had the memory back,” says Travaglia. This suggests that the memory is still there, just not normally accessible.

Travaglia thinks that his findings might apply to us as well. He thinks that the “off days” we experience might result from the subconscious reactivation of unpleasant memories. In other words, some reminder is reactivating a memory we might not consciously know we have.

Andrii Rudenko and Li-Huei Tsai at the Massachusetts Institute of Technology, are impressed, and say that Travaglia’s team have “tackled a century-old question”.

Latent memories

“The study breaks new ground… it shows that very early memories in mammals are not lost but stored as latent traces that can be recalled later,” the pair wrote in a comment piece published in the journal Nature Neuroscience.

Travaglia’s team also compared the brains of young and adult rats, before and after learning. They found that several proteins either increased or decreased in number in the hippocampi of rats – a brain region vital for memory. These changes were triggered by learning, rather than by the passage of time.

One protein, called BDNF, seemed particularly important. When the team injected this protein into young rats it protected their memories, preventing them from being lost with age.

In theory, it might be possible to protect children’s first memories in the same way, says Travaglia. However, he is more interested in finding ways to block or eliminate traumatic memories – although he stresses that he is not ready to test any such approach in humans.

Patricia Bauer at Emory University in Atlanta, Georgia, doubts the findings can be applied to people, because human memory and rat memories are very different. “The work is very elegant, and tells us a lot about the development of the hippocampus,” she says. “But it doesn’t tell us anything about infantile amnesia.”

Jonathan Lee at the University of Birmingham, UK, agrees with Bauer that the rats might not be experiencing true infantile amnesia, but thinks the findings could have other implications for our understanding of human memory. People who seem to have difficulty learning new information could have memories tucked away in their brains, but are struggling to access them, he says.

Journal reference: Nature Neuroscience, DOI: 10.1038/nn.4348