You might think you remember taking a trip to Disneyland when you were 18 months old, or that time you had chickenpox when you were 2—but you almost certainly don’t. However real they may seem, your earliest treasured memories were probably implanted by seeing photos or hearing your parents’ stories about waiting in line for the spinning teacups. Recalling those manufactured memories again and again consolidated them in your brain, making them as vivid as your last summer vacation.
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Intriguingly, infantile amnesia seems to affect only certain kinds of memories, particularly the ones known as contextual memories, which involve connecting cues such as the layout of an environment with events that happen there. In humans, the forgotten memories include episodic memories: conscious recollections of where and when a specific event occurred. In contrast, young brains can recall other types of memories just fine, including semantic memories of the meanings of words and motor memories of skills such as how to draw a circle. “There’s probably an underlying neural timetable of development in various bits of the memory system,” says Nora Newcombe, a psychologist at Temple University. Until recently, the simplest explanation has been that the hippocampus, the brain’s key processing and storage site for episodic and contextual memories, either can’t store these memories or can’t form them in the first place.
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Why most early memories are forgotten in the first place is still unclear, however. The process is too widespread to have emerged without an important reason, says Rick Richardson, a psychologist at the University of New South Wales Sydney. “Evolution doesn’t work that way,” he says.
It’s possible that suppressing memories allows the brain to put more computing power toward figuring out how the world works while giving the hippocampus time to develop, says child psychologist Tracy Riggins at the University of Maryland.