The neural mechanisms that get babies walking are present from birth, which is a new a finding that challenges the way we understand human development.Parents have to wait about a year before the momentous day when their child takes its first steps. But how does a baby learn how to walk, and why does it take so long when other animals can walk shortly after birth? Now an international team of scientists have cracked the riddle, and surprisingly it seems we may be much more similar to other animals than we might like to think.
Research into the neural mechanisms behind our movements not only helps to explain how our bodies work, but could also lead to better ways to help people with spinal injuries. Comparing the way we move to other animals also offers up important clues to our evolutionary past, and demonstrates how animals can make good models for research that might benefit humans.
"The striking similarity we found in human and animal patterns strongly supports the use of animals as experimental models of motor disorders in humans," said Francesco Lacquaniti from the University of Rome Tor Vertega in Italy, one of the authors of the study published today in the journal Science.
Babies walk unaided around a year of age, but newborn babies are also equipped with the ability to generate walking movements. When newborns are held in a standing position with their feet on a firm surface, they produce spontaneous stepping movements.
Until now, most scientists thought that the primitive patterns of nerve signals that lead to automatic walking motions in newborns are discarded as the baby develops, and are replaced by entirely new patterns later on.
However, Lacquaniti and his team have shown that in fact, the primitive patterns seen in newborns are not discarded but instead are retained and fine-tuned during development, when new patterns are also added.
How do we walk?
The study also sheds new light on the way that our walking mechanisms evolved. Because it takes humans such a long time to learn to walk, it was thought that the neural control of human walking mechanisms is very different to that of other animals and that new neural circuits develop in the year following birth.
However, this study proves the idea to be a misconception and shows just how similar our own neural circuits for locomotion are to those of other animals, suggesting these traits evolved from common ancestral mechanisms in the remote past.
To find out exactly how locomotion develops right from birth, the team used a non-invasive method called Electromyography (EMG) to measure the electrical activity in around 20 different muscles involved in walking in toddlers ready to make their first steps, older children and adults. They compared these to the muscles of three-day-old babies making automatic stepping actions as they are supported over a solid surface. The team also compared the patterns of locomotion of children with those of three quadrupedal mammals – rats, cats and macaques – as well as a bipedal bird – guinea foul, to see how they differed from the nervous systems of humans.
Preserved patterns
When the team compared the patterns of newborns to those of toddlers and children, they were surprised to find that the primitive signals that generate walking motions in newborns are not discarded during development.
The comparison of human walking mechanisms with animals also led to some surprising results – even in animals that walked on four legs, the basic activation patterns were very similar to those of human children. "The striking similarities we found across animal species which are so distant from an evolutionary standpoint suggest that the neural circuits which generate locomotion emerged during evolution from a common ancestral network of neurons," said Lacquaniti.
The fact that early patterns seen in babies are in fact preserved during development is an important finding, commented Martin Garwicz, from Lund University in Sweden.
Why does it take so long?
But if the brain is not developing entirely new neural circuits during this time, why is it that babies don't put these primitive circuits into practice for several months? According to an analysis of the research paper written by Sten Grillner from the Karolinska Institute in Sweden, and published in the same issue of Science, "It appears the brain must reach a certain degree of maturity before the ability to walk can be manifested."
He said this is linked to brain weight – an idea backed up by previous research by Garwicz and his colleagues, which showed that the only animal that takes longer to learn to walk than humans, taking into account the time of conception, is the elephant.
All these findings challenge the dogma that human postnatal development of locomotion must be different from that in other mammals since we walk on two legs, have an unusually large brain and develop during a long period of time, said Garwicz.
As well as challenging accepted wisdom, the results could potentially also benefit those who have difficulty walking, and supports the use of animals in research. "We hope, but it is only a hope for now, that the discovery of the signals used by the central nervous system to control muscles and locomotion may help designing better tools for rehabilitation, functional electrical stimulation, and prosthetics for patients with spinal cord injuries and other neurological diseases which impair locomotion," Lacquaniti said.
No comments:
Post a Comment