What scientists know about infantile amnesia

Whenever I teach memory in my child development class at Rutgers University, I open by asking my students to recall their first memories. Some students talk about their first day of pre-K; others talk about a time when they were hurt or upset; some cite the day their younger brother was born.

Despite the great differences in detail, these memories have several things in common: they are all autobiographical, or memories of important experiences in a person’s life, and they usually did not occur before the age of 2 or 3. Most people can remember events from the first years of their lives – a phenomenon that researchers have called infantile amnesia. But why can’t we remember things that happened to us when we were babies? Does memory only start working at a certain age?

Here’s what researchers know about babies and memory.

While people can’t remember much before age 2 or 3, research suggests that babies can form memories — just not the kinds of memories you tell about yourself. Within the first days of life, babies can remember their mother’s face and distinguish it from the face of a stranger. A few months later, babies can demonstrate that they remember many familiar faces by smiling mostly at those they see most often.

How learning happens in the brains of sleeping babies

There are many different types of memoir besides those that are autobiographical. There are semantic memories, or memories of facts, such as the names of different varieties of apples, or the capital of your state. There are also procedural memories, or memories of how to perform an action—think opening your front door or driving a car.

Research from psychologist Carolyn Rovee-Collier’s lab in the 1980s and 1990s famously showed that babies can form some of these other types of memories from an early age. Of course, babies can’t tell you exactly what they remember. So the key to Rovee-Collier’s research was designing a task that was sensitive to infants’ rapidly changing bodies and abilities to assess their memories over a long period.

In the version for 2- to 6-month-old babies, researchers place a baby in a crib with a cell phone hanging over it. They measure how much the child kicks to get an idea of ​​their natural tendency to move their legs. They then tie a string from the baby’s leg to the bottom of the mobile so that every time the baby kicks, the mobile moves. As you can imagine, babies quickly learn that they are in control – they love to see the mobile move and so they kick more than before the cord was attached to their leg, showing that they have learned that kicking makes the mobile move.

Sleep training can benefit some babies—and their parents

The version for children from 6 to 18 months is similar. But instead of lying in a crib—which this age group refuses to do for a long time—the baby sits on their parents’ laps with their hands on a lever that will eventually make a train move through rail. At first, the lever does not work, and the experimenters measure how much a child presses naturally. Then, they turn on the lever and every time the baby presses it, the train moves around its tracks. Babies again learn the game quickly and press the lever significantly more when it makes the train move.

What does this have to do with memory? The clever part of this research is that after training the babies on one of these tasks for several days, Rovee-Collier later tested whether they remembered it. When the toddlers returned to the lab, the researchers showed them the cell phone or the train and measured whether they still kicked or pressed the lever.

Using this method, Rovee-Collier and colleagues found that at 6 months, if babies are trained for one minute, they can recall an event a day later. The older the babies were, the longer they remembered. She also found that training babies for longer periods of time and giving them reminders – for example, showing them the mobile by moving very briefly on its own – helps them remember events longer.

Why not autobiographical memoirs?

If babies can form memories in their first months, why don’t people remember things from that early stage of life? It’s still not clear whether people experience infantile amnesia because we can’t form autobiographical memories, or if we simply have no way to retrieve them. No one knows for sure what’s going on, but scientists have some guesses.

Is my memory failing or is it just normal aging?

One is that autobiographical memories require you to have some sense of yourself. You need to be able to think about your own behavior in relation to how it relates to others. Researchers have tested this ability in the past using a mirror recognition task called the rouge test. It involves marking the baby’s nose with a smear of red lipstick or blush – or “red” as they said in the 1970s when the task was created.

The researchers then place the baby in front of a mirror. Babies younger than 18 months simply smile at the cute baby in the reflection, showing no sign of recognizing themselves or the red mark on their face. Between 18 and 24 months, toddlers touch their noses, even look embarrassed, suggesting they associate the red dot in the mirror with their face—they have a sense of self.

Another possible explanation for infantile amnesia is that because babies don’t have language until later in their second year of life, they can’t create stories about their lives that they can later recall.

Finally, the hippocampus, which is the region of the brain primarily responsible for memory, is not fully developed in infancy.

Scientists will continue to investigate how each of these factors may contribute to why you may not remember much, if anything, about your life before age 2.

This article was originally published on theconversation.com.

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