Remember When? The nature of early memory

What do babies remember—and when? Most adults’ earliest memories are of being a toddler or preschooler. Before the third or fourth year, the brain isn’t mature enough to store long-term memories. In addition, babies lack language, and their memories are not attached to words; they are not in a format we can access as adults.

Remember this?

There is some evidence, however, of even newborns having rudimentary memory, say specialists in infant memory. How do experts know when an infant remembers something? Research has shown that newborns can learn to suck on a pacifier at a certain rate in order to hear a recording of their mother’s voice. This ability to associate their own actions with a memory of something they desire allows researchers to study what babies remember as they grow and develop.

Dancing mobiles

One classic experiment that demonstrates that babies do remember events, and can act on these memories, studies infants lying in their cribs under a brightly colored mobile. A soft ribbon is strung between the infant’s ankle and the mobile’s crossbar. Babies soon learn that the more they kick, the more the mobile moves as the ribbon pulls it. They adore watching the dancing mobile, and kick with vigor to make it move even more.

Researchers wanted to know how long babies would recall that their kicks make the mobile move. They found that after one “training session,” infants as young as 2 months would remember for a day or two, while a 6-month-old would kick up a storm when reintroduced to the same mobile as much as two weeks later.

New and different

Another way in which infant memory is studied is based on a universal parental observation: babies love novelty. Infants soon tire of the “same old, same old” and are driven to seek and explore new things and experiences.

In order for researchers to determine what is new, however, babies must be able to recognize, and remember, what is familiar. Throughout infancy and childhood, this “recognition memory” continues to grow steadily. While a newborn may need to stare at a new stimulus for many minutes in order to recognize it just a few minutes later, a 6-month-old can store this information in a few seconds and recognize the stimulus up to two weeks afterward.

Brainy babies

Researchers are learning more about how memory develops by going straight to the source: the brain itself. At the University of Minnesota’s Center for Neurobehavioral Development, colorful hairnets threaded with electrodes measure how babies’ brains react to what they see and hear. Infant brain waves differ, the data shows, when they see novel, rather than familiar, objects and faces.

Interestingly, comparing memory development of infants born to healthy mothers with that of infants born to diabetic mothers reveals which parts of the brain make memory possible. Depending on how well a woman’s diabetes is controlled during pregnancy, her fetus may experience iron deficiency and other factors that affect the development of the part of the brain involved in memory formation. The differences in development of these two groups of babies pinpoints the role of this area of the brain in the ability to form and store memories.

Eight months and beyond

While young babies certainly take in, store, and adapt to a lot of information, they are not yet consciously aware of it, researchers say. It’s not until a baby’s brain has matured to the point that he or she is capable of conscious, or explicit, memory—what we generally think of when we refer to “memory” in adults—that true recall begins to emerge.

Unlike earlier recognition memory, when an infant must look at, hear, feel, smell, or taste something to know whether he has experienced it before, a baby of 8 months or so begins to remember faces, words, objects, and other stimuli without reencountering them with his physical senses. Indeed, as babies approach their first birthday, they are able to use experiences derived from one sense to build memories that draw on another sense. One study explores this remarkable ability to make connections between the senses of touch and sight. After feeling (but not seeing) 11 different wooden geometric shapes, healthy 8-month-old babies were able to recognize visual images of the objects they had held in their hands, but did not recognize images of objects they had not touched.

Equally thrilling at this age is the mastery of “object permanence”—a baby’s ability to hold a representation of an object (or a person) in mind after it is no longer in view. As parents of older infants are well aware, playtime becomes exponentially more fun when babies reach this point—when they can remember that there’s a toy hidden under that blanket, or gleefully engage in a game of peek-a-boo.

Researchers agree that everyday interaction between babies and caretakers is the ticket to healthy development of infant memory. Talking to babies, playing with them, and reading to them provide just the right amount of stimulation and intellectual challenge—and babies’ lasting memories.

Sources: Pediatric Research 55 (2004): 1034–41; Journal of Pediatrics 142 (2003): 575–82; personal interview with Charles A. Nelson, Ph.D., April 4, 2005.

The Parent Review newsletter publishes the latest research findings in child development, learning, and health. Written for expectant and new parents and the professionals supporting them, The Parent Review bridges science and parenting to offer the best and most relevant research-based news. To learn more, visit www.theparentreview.com.

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