人类早期记忆的谜团

童年期遗忘的谜团过去一个世纪以来一直困惑着科学家们。为什么在人类的幼儿期，一个充满体验和学习新事物的阶段，却被许多难以理解的事物而笼罩？

What is your earliest memory? For me, I have a hazy recollection of standing in a leafy garden surrounded by silver birch trees when I was four years old.

I'm around average: some people remember events as far back as two years old, while for others, things seem patchy until seven or eight.

But what is consistent is that no one can remember their own birth or very early infancy. And even after the first memory, most of us only have a sporadic collection of fleeting, flickering mental images until much later in childhood.

The phenomenon is known as 'childhood amnesia', a term coined by the father of psychoanalysis, Sigmund Freud. So, what's going on here?

Babies are, writes Zaria Gorvett for BBC Future, "sponges for new information, forming 700 new neural connections every second and wielding language-learning skills to make the most accomplished polyglot green with envy".

And it's precisely this rapid mental development that causes the problem, according to a study by the University of Toronto in 2014. It found that the high rate of infant brain cell production could increase forgetfulness, because new cells interfere with existing mental circuits.

Another possible explanation is that the part of the brain that stores memories, the hippocampus, is not fully formed until around 18 months. Identity is also important: tests show infants don't recognise themselves in the mirror until they are around two years old.

Finally, there's the question of how accurate our early memories are at all. "People can pick up suggestions and begin to visualise them - they become like memories," psychologist Elizabeth Loftus told the BBC. Are our cherished first memories really just family stories?