These early abilities do not quite add up to what we think of as conscious memory — the skill that allows us to recite the U.S. capitals or reminisce about summer camp. Performing well on the mobile test does not require conscious memory. In fact, it doesn't require a cerebral cortex. Even though a baby is born with most of the brain cells she will have as an adult, for the first few months of life the cortex (the big grey mass we use to think) is largely offline. Lower parts of the brain and the spinal cord control most of a newborn's behavior, allowing her to form habits and develop motor skills. Our first memories are formed in these primitive parts of the brain.

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Lise Elliot, Associate Professor at the Chicago Medical School and author of What's Going On In There? How the Brain and Mind Develop in the First Five Years of Life, explains that these unconscious patterns — like when baby's legs kick at the sight of her favorite toy — are part of what is called implicit memory. "Anything you learn is said to store a memory," explains Eliot. "But we distinguish conscious and unconscious memory. Probably ninety percent of what we do happens at this unconscious level, especially in young children."

This kind of memory takes repetition to develop, but requires little thought once it's in place. Implicit memory is how you tie your sneakers or write an email without thinking about your hands, and without any sense that memory is involved. A little kid's mind is bustling with implicit memories in the early years, but the impact goes further than just motor skills. These lower brain regions cozy up to our feeling centers too, so kids learn emotional patterns way before they become conscious beings.

It's hard to know for sure, but some argue that a baby's conscious, or explicit, memory starts to develop at about eight months. Older infants not only recognize something when it's in front of them; they can actually conjure up mental images of the people, places, or objects in their lives. Kids learn emotional patterns way before they become conscious beings. If you show a nine-month-old baby how to use a certain toy (but don't let her touch it) and then give the toy to her twenty-four hours later, she will know what to do with it, presumably because she has the mental picture of you playing with it. Amazingly, at fifteen months, a baby can actually remember the toy tricks after a four-month delay.

These leaps are possible because more signals are starting to reach the cortex and important memory regions are coming online. One of these regions is the hippocampus, an area of the brain that doctors removed to cure H.M.'s epilepsy. "Everything has to go through there to get shuttled into permanent storage," says Eliot. At the time, scientists didn't know what this region did, but they would soon find out that it is necessary for conscious recall — it allows you to remember a friend's birthday or what you had for breakfast.

Scientists were surprised, though, when they realized that H.M. was still capable of forming certain kinds of memory. He could learn new skills and get better at certain tasks. As part of a research project, for example, he got very good at drawing a figure while looking at its reflection in the mirror. Every time he did this it was as if for the first time, and it surprised him that he could do it so easily. His implicit memory was intact, so he could learn and improve, but without a hippocampus he couldn't recall ever having done the drawing exercise before.