November 17th, 2011
04:15 PM ET
Children typically start walking independently when they are about 1 year old. But scientists say that even healthy newborns have the capacity to start stepping and have a pattern of neural activity similar to that of other animals.
Research published in the journal Science suggests that baby humans, rats, cats, macaque and guinea fowl all share similar neural mechanisms for locomotion. Human adults, on the other hand, have a distinct pattern of signals, which is derived from the basics seen in babies.
"We have a common history ... a common ancestral network, which originated locomotion in the first animals, the first vertebrates," said study co-author Francesco Lacquaniti, scientist at the University of Rome Tor Vergata in Italy.
"Mother nature did not discard what it had. It does not scrap hardware," he added. "Indeed, the adult locomotion of adults is unique. But it seems to derives from common ancestry, as for the other animals."
Researchers looked at healthy babies between 2 and 7 days old. They used an electromyograph to monitor the electrical activity of the babies' muscles. Then, a pediatrician lifted the child and lowered him or her on the table. As soon as the baby's feet touched the table, he or she would start stepping.
Motor neurons, which send signals to muscles, have the basic commands ready in a newborn baby. But only half the circuitry for walking is ready at birth, Lacquaniti said. In fact, the stepping reflex disappears a few weeks after birth. It then reappears as intentional walking at about 10 months, the time it takes for the nervous system to mature and develop the signals missing at birth.
Lacquaniti and colleagues also looked at toddlers, older children and adults and saw how the patterns of the infants get modified and adapted as a child ages. In adult walking, the pulses of activity are shorter than in babies, which is useful for the older folks because less energy is spent.
"This is why babies start walking at 1 year of age, but they wobble," Lacquaniti said. "It takes several more years to then fine-tune and develop adult-like commands, which are much briefer."
Researchers wanted to see how this process of the development of locomotion compares to that of other animals. They looked at rats, cats, macaque and guinea fowl and found similar patterns of neural activity as in newborn human babies.
A 2-year-old human child is smarter than an adult monkey, but the two have comparable locomotive abilities, Lacquaniti said. Separate research has shown that the bigger the animal's brain, the longer the time after fertilization required to develop independent locomotion.
This does not mean humans walk better than other animals. In fact, there are significant costs associated with moving with two legs instead of four: for instance, greater instability and back pain because we have to sustain the weight of our bodies.
There are clinical implications to all this. Understanding the neural mechanisms of walking can help with developing rehabilitation tools for people who are paralyzed and cannot walk.
"If one knows the exact shape of the neural commands, one hopes to use similar commands in prosthetic limbs, retrain the paralyzed patient to relearn to walk, so to speak," Lacquaniti said.
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