学进去

Why can’t you remember being a baby? Will that trip to Dreamworld be wasted on your toddler (学步的幼儿)? Scientists explain how the brain changes from infancy (婴儿期) through to early childhood, and what this means for your child’s memories.

While some people can remember memories from as early as age two, as adults most of us rarely remember things that happen to us before the age of three, due to a phenomenon called “infantile amnesia (婴儿健忘症)”. Generally, we tend to have vague (模糊的) memories of events that occur between the ages of three and seven.

So why is it that we can’t remember being a baby, or a toddler? The answer lies in the way that our brain’s ability to store memories changes as we grow. At birth, a baby’s brain is only a quarter of its adult size, growing to three-quarters the size of an adult brain by age two. This increase correlates with a growth in the number of brain cells—called neurons (神经元)一and the connections between these cells.

A part of the brain that is important in forming memories is the hippocampus (海马体), says Dr Dhanisha Jhaveri, a researcher at the Queensland Brain Institute at The University of Queensland. “In the hippocampus, new neurons are constantly being created. In adulthood, new cells are still being produced, but the rate of production in the hippocampus slows down,” says Dr Jhaveri.

Neuroscientists believe that the rapid rate at which brain cells are being produced in childhood could be the cause of infantile amnesia. Because so many new neurons are being produced and form connections with each other in memory circuits (记忆电路), they might disturb existing networks of memories that have already formed.

But it turns out that a child’s ability to remember things for long periods of time improves gradually throughout childhood. For example, in studies in which young kids were taught to imitate an action, six-month-olds could remember what to do for 24 (but not 48) hours, while nine-month-olds could remember what to do one month (but not three months) later.

Despite this memory loss, childhood experiences have been found to influence adult behaviour years later, which suggests that traces of these memories could be stored somewhere in the brain that isn’t easy to access.

So while your kids might not recall their major milestones or be too young to remember a trip to Disneyland, positive experiences as toddlers or in infancy may continue to affect their behaviour long after they’ve forgotten them.