My earliest memories are more like nostalgic flickers. The sunlit kitchen and living room of my childhood home. The candle I burned my finger on. The plastic toy set that occupied my playtime. These disparate and vague recollections are all most of us can remember of our first years of life. But a recent conversation with a friend, who swore they could recall, in detail, a car journey when they were just 18 months old, got me thinking about whether childhood amnesia is a universal experience. Why do our young brains, which are so adept at learning about the world, fail to retain the memories we make during this essential period of development?

Infantile amnesia or childhood amnesia?

Sarah Power, a postdoctoral researcher in the Department of Lifespan Psychology at the Max Planck Institute for Human Development, has studied early memory in rodents and humans. She explains that researchers have previously used the terms childhood amnesia and infantile amnesia interchangeably. Power prefers to separate them, with childhood amnesia referring to the blurry memories we have of when we were between three and six years old. In contrast, infantile amnesia refers to our memories before the age of three, which are thought to be irretrievable.  

Power has previously worked with infant rodents and shown that these young animals can record memories, although they cannot consciously access them in adulthood. Other studies show that altering the levels of specific brain receptor proteins in mice can allow the animals to access these memories and change their behavior in response.

False memories

Unlike rodents, you can ask humans if they remember their childhood. Nevertheless, human studies have their own problems. A challenge with recollections of childhood, Power explains, is that we can trick ourselves into thinking others' memories are our own. 

"If you keep seeing a picture of your second birthday, or your parents are always talking about some other event, you can create these false memories, and every time you then recall them, you are strengthening that memory," says Power. 

Unrecorded subsets of the population may have memories from before this age, says Power, but proving this experimentally requires specific and convoluted experimental design. To examine how children make and keep early memories, Power has built a playroom in her lab that can be turned into an underwater kingdom or dense jungle through projections on the walls. A toy is hidden in one of four boxes in the room. 

Depending on which projection is shown, kids will find the toy in different boxes. Power's test will assess whether a child returning to the lab will remember which box the toy was in during their first visit. Power designed everything in the lab, including the toy, specifically for this study.