Babies can form memories, and they do it a lot like adults

A baby’s early life has a lot of milestones: first giggle, first tooth, first step. A brain scanning study adds to the list: first memory.

Infants can form memories, and they use a memory structure in the brain called the hippocampus to do it, researchers report in the March 21 Science. The results shore up the idea that memories can in fact be made during the earliest years of our lives, though what happens to these memories as the days, weeks and years roll by remains mysterious.

“What is really new in this paper is that it implicates the hippocampus in the encoding of early memories,” says developmental and cognitive scientist Vladimir Sloutsky of Ohio State University in Columbus. And that’s important, Sloutsky says, because it shows the hippocampus “is mature enough to encode early memories.”

Young babies can be difficult research subjects. But for the new study, awake babies were kept calm in functional MRI scanners with a parent nearby and earphones to protect them from startling sounds. In the scanner, these babies, who ranged from 4 months old to nearly 25 months old, saw images, one after another, of people, places or objects. All the while, scientists recorded blood flow in the babies’ brains, a proxy of neural activity.

Occasionally, the babies were tested with a pair of images, one of which they had seen before. If the babies looked longer at the previously seen image, researchers reasoned, they likely remembered it. “We can kind of quantify the strength of their memory based on how much they look at it,” says study coauthor Nick Turk-Browne of Yale University. “And then the trick in this sort of study is to then go back and look at, when they first saw the picture, what was different in the brain for pictures that they later had a memory for, versus that they later forgot?”

The difference, it turns out, was in the babies’ hippocampi, seahorse-shaped structures, one on each side of their brains. In the study, 13 babies were younger than a year, and 13 babies were older than a year. The older babies could remember about half of the images they had seen before. And this memory feat corresponded to brain activity in a part of the hippocampus.

The results add to other evidence that babies, the human sort as well as rats and mice, can in fact form memories, and starts to answer how. Added to earlier research, the new study shows “that in humans, like previously found in rats and mice, infant learning actively engages the hippocampus to form memories,” says neuroscientist Cristina Alberini of New York University.

Still, the results don’t explain why we can’t recall some of the earliest moments of our lives, a phenomenon known as infantile amnesia. It’s possible that these memories aren’t effectively stored elsewhere in the brain. Or it could be that neural traces persist but aren’t able to be called back up.

This second idea is out there, but there’s some evidence for it, Turk-Browne says. Scientists have successfully reactivated infant memories in mice by stimulating the memory trace with light. It’s possible that “there may be sort of fragments of early memories that are still in your brain, and that with the right kinds of cues, or in the case of animals with stimulation, you could reactivate those memories later in life.” He likens the process to an unsuccessful internet search. “The search terms your brain is using to access the memory are wrong or different from what they were when you initially stored the memory.” Turk-Browne and his colleagues are now studying how long babies’ memories might last.