Why don't we remember being babies?

Your mother's smile as you say your first word or the smell of the candles on your second birthday cake are memories many people would love to hold onto. But almost nobody can recall memories from very early childhood — a phenomenon known as infantile amnesia.

So why do we tend to forget these very early memories? It's not because we don't retain information as young children. Rather, it's likely because at that age our brains don't yet function in a way that bundles information into the complex neural patterns that we know as memories.

Young children do remember facts in the moment, such as who their parents are, or that one must say "please" before mom will give you candy. This is called "semantic memory."

Until sometime between the ages 2 and 4, however, children usually lack "episodic memory" — memory regarding the details of a specific event. Such memories are stored in several parts of the brain's surface, or "cortex." For example, memory of sound is processed in the auditory cortexes on the sides of the brain, while visual memory is managed by the visual cortex at the back. A region of the brain called the hippocampus ties all the scattered pieces together.

"If you think of your cortex as a flower bed, there are flowers all across the top of your head," Patricia Bauer, a professor of psychology at Emory University told Live Science. "The hippocampus, tucked very neatly in the middle of your brain, is responsible for pulling those all together and tying them in a bouquet." The memory is the bouquet — the neural pattern of linkages between the parts of the brain where a memory is stored.

Related: How accurate are our first childhood memories?

Kids may fail to record specific episodes until the 2-to-4 age range because that's when the hippocampus starts tying fragments of information together, Nora Newcombe, a professor of psychology at Temple University in Philadelphia told Live Science.

Newcombe said that, for children younger than that age range, episodic memory may be unnecessarily complex at a time when a child is just learning how the world works.

"I think the primary goal of the first two years is to acquire semantic knowledge and from that point of view, episodic memory might actually be a distraction," Newcombe said. 

However, another theory suggests that we actually store these early memories as kids but struggle to recall them as adults. For example, a 2023 study, published in the journal Science Advances, found that "forgotten" childhood memories could be reinstated in adult mice by stimulating neural pathways that are relevant to specific memories with light. 

The authors of the study first set out to explore developmental factors that could influence infantile amnesia. They found that mice with characteristics of the neurodevelopmental condition autism spectrum disorder (ASD) were able to recall memories from their pup days.

Autism has many causes, but it has been previously linked to the over-activation of the mother's immune system during pregnancy. So, to make mice with ASD, the researchers stimulated the immune system of female mice during pregnancy.

This immune activation helped prevent the loss of early memories in these offspring by influencing the size and plasticity of specialist memory cells in their brains. When these cells were optically stimulated in adult mice without autism, forgotten memories could be restored.

"These new findings suggest that immune activation during pregnancy results in an altered brain state that alters our innate, yet reversible 'forgetting switches' that determine whether the forgetting of infant memories will occur," study co-author, Tomás Ryan, an associate professor of biochemistry at Trinity College Dublin in Ireland, said in a statement. 

While the research is in mice and has yet to be studied in humans, it "holds significant implications for enhancing our comprehension of memory and forgetting across child development, as well as overall cognitive flexibility in the context of autism," Ryan said.

Editor's note: Originally published on Feb. 7, 2011 and updated on Nov. 27, 2023 to include the new study about autism.