Why do babies kick in the womb? New study solves age-old mystery, with implications for the future

LOS ANGELES — Scientists are finally able to explain why babies really kick in their mother’s womb. Researchers from USC say they believe the act “wires up” the nervous system. Moreover, the discovery may be the key to treating neurological illnesses and even training more agile robots.

Babies can kick with a force of more than 10 pounds, a phenomenon that has mystified scientists for centuries. Now, a model shows it helps the infant learn to control its body.

“The complex circuits of the nervous system are not pre-determined by genes but rather are reinforced by body movements,” researchers write in a university release.

The discovery sheds light on a host of disorders, from cramps and spasms to multiple sclerosis, spinal cord injuries, and motor neuron disease. The hundreds of neurons that control each muscle are synchronized in the fetus to create strong contractions that activate “sensors.”

“These correlated patterns of activity can be used to wire up the spinal cord circuitry that coordinates the muscles through reflexes,” according to the team, led by Prof. Henrik Jörntell of Lund University and Gerald Loeb of USC. “The brain can then use that circuitry to learn voluntary movements that are well-coordinated, graceful and efficient.”

Showing how the body learns and adapts builds on an evolutionary theory first put forward by legendary American psychologist James Mark Baldwin in 1896. It suggested a newborn animal with a potentially useful mutation of the musculoskeletal system must reproduce and propagate it. If the animal’s nervous system were hardwired for the old body, it probably wouldn’t survive.

“The new model outlines how neural circuits in the spinal cord can learn the mechanics of the new body from its early, spontaneous movements,” researchers continue. “This new model of development has implications for how to treat neuromuscular disorders and could also provide a simple way to design better controllers for robots.”

Giving robots smarter nerve circuits

The international team is now investigating how the brain learns to wire itself to the spinal cord.

They add that figuring this out is, “another in the many steps required to build a complete nervous system capable of intelligent behavior which can automatically separate a notion of ‘self’ from the notion of ‘world’.”

Study authors also hope it will lead to a better understanding of developmental problems such as cerebral palsy and the difficulties of recovering from spinal cord injuries and strokes.

To date, it has been difficult to get robots to perform movement tasks that humans do easily. The spinal cord is more than just a cable connecting brain to muscles. It contains complex networks that generate everything from simple knee-jerk reflexes during medical exams to walking and other more advanced movements.

“The brain learns to use these spinal circuits to generate the graceful and efficient behaviors that we take for granted,” researchers explain. “Robots are often clumsy because they lack such circuits. The circuits of the spinal cord can’t be applied to a robot because the mechanics of the robot are different from animals.”

The computer simulations provide a way for any robot to replicate the stages of human development to spawn the equivalent of spinal circuits for its body.

Most pregnant women begin to feel their baby move between 16 and 24 weeks. The movements range from a kick, flutter, swish, or roll, which may change as the pregnancy progresses.

The findings are published in the Journal of Neurophysiology.

South West News Service writer Mark Waghorn contributed to this report.

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