The first study to systematically mark the onset of "childhood amnesia" found that by the time children are 10, their preschool memories have already faded away.

"I expected that they would differ, but there's a striking similarity in the age of the earliest memory for adults and 10-year-olds," researcher Dr. Carole Peterson, a psychologist at Memorial University of Newfoundland, Canada, said in a prepared statement.

She said her findings from a study of 136 children ages 6 to 19 years old further deepen the mystery surrounding childhood amnesia, which refers to adults' inability to recall events that occurred before the age of 4. Peterson noted that 3- and 4-year-old children can easily recall events from their second year. However, by the time children are 10 years old, these earliest memories are gone.

"We don't have any good models to explain this. The memories were there and had been verbally accessible. So, why aren't they there any more?" Peterson asked.

She noted that parents can influence which of their children's memories become lifelong ones. The more parents talk with their children about particular experiences, the more likely that this verbal reinforcement will help preserve children's early memories.

"Talking a lot about your experiences, encoding them in language, has an impact on preserving the memory, there's no doubt about that. But this doesn't solve the mystery of why it is that something that you could remember and talk about at one stage, disappears later," Peterson said.

The study was published in a recent issue of Memory.

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