What scientists know about infantile amnesia

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

Despite vast differences in the details, these memories do have a couple of things in common: They’re all autobiographical, or memories of significant experiences in a person’s life, and they typically didn’t happen before age 2 or 3. Most people can’t remember events from the first few years of their lives — a phenomenon researchers have dubbed infantile amnesia. But why can’t we remember the things that happened to us when we were infants? Does memory start to work only at a certain age?

Here’s what researchers know about babies and memory.

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

How learning happens in the brains of sleeping babies

There are lots of different kinds of memories 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 home 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 infants can form some of these other kinds of memories from an early age. Of course, infants cannot exactly tell you what they remember. So the key to Rovee-Collier’s research was devising a task that was sensitive to babies’ rapidly changing bodies and abilities to assess their memories over a long period.

In the version for 2- to 6-month-old infants, researchers place an infant in a crib with a mobile hanging overhead. They measure how much the baby kicks to get an idea of their natural propensity to move their legs. Next, they tie a string from the baby’s leg to the end of the mobile, so that whenever the baby kicks, the mobile moves. As you might imagine, infants quickly learn that they’re in control — they like seeing the mobile move and so they kick more than before the string was attached to their leg, showing they’ve learned that kicking makes the mobile move.

Sleep training could benefit some babies — and their parents

The version for 6- to 18-month-olds is similar. But instead of lying in a crib — which this age group refuses to do for very long — the infant sits on their parent’s lap with their hands on a lever that will eventually make a train move around a track. At first, the lever doesn’t work, and the experimenters measure how much a baby naturally presses down. Next, they turn the lever on, and every time the infant presses on it, the train moves around its track. Infants again learn the game quickly and press on the lever significantly more when it makes the train move.

What does this have to do with memory? The cleverest part of this research is that after training infants on one of these tasks for a couple of days, Rovee-Collier later tested whether they remembered it. When the little ones returned to the lab, researchers showed them the mobile or train and measured whether they still kicked or pressed the lever.

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

Why not autobiographical memories?

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

Is my memory going or is it just normal aging?

One is that autobiographical memories require you to have some sense of self. You need to be able to think about your behavior with respect 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 a baby’s nose with a spot of red lipstick or blush — or “rouge” as they said in the 1970s when the task was created.

Then researchers place the infant in front of a mirror. Infants younger than 18 months just smile at the cute baby in the reflection, not showing any sign they recognize themselves or the red mark on their face. Between 18 and 24 months, toddlers touch their own nose, even looking embarrassed, suggesting that they connect the red dot in the mirror with their own face — they have some sense of self.

Another possible explanation for infantile amnesia is that because infants don’t have language until later in the second year of life, they cannot form narratives about their own lives that they can later recall.

Finally, the hippocampus, which is the region of the brain that largely is responsible for memory, isn’t fully developed in the infancy period.

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

This article was originally published on theconversation.com.