Why Do Infant Memories Disappear, Yet Quietly Shape Our Future?

Most people cannot recall any events before the age of three or four, a phenomenon known in science as infantile amnesia. For centuries, scientists believed infant brains were not developed enough to store memories, leading to the disappearance of childhood recollections. However, a recent study on mice published in Neuron has debunked this theory. The research shows that seemingly lost infant memories persist in the brain, forming hidden templates that influence learning in adulthood.

Laboratory mice exhibit a similar forgetting pattern to humans. A young mouse can learn something at three weeks old, but the memory appears to vanish from its behaviour a month later. In the experiment, researchers trained young mice in a special chamber by administering mild electric shocks to their feet, teaching them the space was unsafe. Weeks later, the fear response (freezing) faded. When tested again as adults (60 days later), the mice no longer showed fear, suggesting the childhood memory had been erased.

However, everything changed when researchers provided a subtle cue. The adult mice were briefly returned to the original experimental chamber without shocks. Surprisingly, days later, they exhibited strong fear responses again. The childhood memory was successfully reactivated by the same environmental cues.

Previously, the hippocampus was considered the gatekeeper of memory. But research from Cristina M. Alberini’s lab at New York University (NYU) revealed a new direction. By tracking active neurons, scientists found that early memories are stored and retrieved by the prefrontal cortex—the area behind the forehead responsible for planning and decision-making. When neurons in the prefrontal cortex were deactivated, the memories failed to resurface. Inactivating the hippocampus had no such effect.

Another surprise was that adult mice with reactivated childhood memories learned related new tasks more quickly. Alberini’s team called this phenomenon a “memory schema.” This schema acts as a template established in infancy, reused by the brain when facing similar situations in adulthood. This unique pattern was not observed in mice trained only as adults.

The findings have significant implications for child development. Although events from the first three years of life cannot be consciously remembered by adults, childhood experiences and environments are never erased. These early experiences persist as silent structural layers in the brain, shaping future intelligence.