The Theory of Neuromuscular Maturation

Believe it or not, it is only relatively recently that scientists have begun to appreciate the importance of babies' earliest motor activity. In the first part of this century, most researchers championed the view that motor development is largely innate, or "hard-wired." Struck by the remarkable consistency of skill acquisition, they argued that motor development depends solely on a fixed process o{ neuromuscular maturation (as their theory came to be called). with little role for practice or experience.

One 1940 study was often cited as supporting the neuromuscular maturation theory: an analysis of walking in Hopi Indian babies. Traditionally, a Hopi baby spends much of her first year as a papoose—strapped to the mother's back in a cradleboard in which she can barely move. Despite this confinement, researchers found that Hopi babies reared in the traditional manner developed no differently from those reared in Western fashion, without the cradleboard: both groups of babies began walking at fifteen months, which is a little late but still within the normal range. Of course, the traditionally reared babies were not swaddled during all hours of the day; in the early months, they were removed for bathing and changing, while in later months, they spent several hours each day outside the cradleboard, and few were cradled at all beyond nine months of age. Nonetheless, this study convinced many early researchers that practice and muscular exercise are relatively unimportant in determining when motor skills emerge.

If motor restrictions have little effect, what about the opposite—intensive exercise in early life? As another way of testing their theory, researchers in the 1930s used identical twins for some remarkable training experiments. In each study, one twin was extensively helped and encouraged to practice at a particular skill—like rolling over, sitting, standing, stair-climbing, blockbuilding, tricycle-riding, or potty use—while the other twin received no special training. Despite their lengthy workouts, the trained twins were no more advanced in their motor skills than their siblings who spent their infancy in comparative leisure. This was particularly true for more basic abilities, such as walking and standing. So again researchers concluded that it is the fixed pace of neuromuscular maturation that determines a baby's motor progress; all the practice in the world isn't going to accelerate a particular motor skill if the baby's brain and muscles are not developed enough.

Lise Eliot, What's Going on in There? : How the Brain and Mind Develop in the First Five Years of Life (2000-10-03)

• babies
• infant development
• parenting