Study finds why babies kick, wiggle and move in the womb

Spontaneous baby movements have a purpose.


Follow us onFollow Tech Explorist on Google News

Babies begin to kick, wiggle, and move seemingly aimlessly and without external stimulus as soon as they are born and even while still in the womb. These are referred to as “spontaneous movements,” and scientists think they are crucial to the growth of the sensorimotor system—our capacity to regulate our muscles, movement, and coordination.

Understanding these random movements and their involvement in early human development could help identify early indicators for certain developmental disorders, such as cerebral palsy.

A new study by the University of Tokyo suggests that spontaneous, random baby movements aid the development of their sensorimotor system. Scientists integrated a detailed motion capture of newborns and infants with a musculoskeletal computer model to study muscle communication and sensation throughout the entire body.

Spontaneous movements
Spontaneous movements. The markers for the motion capture camera were gently applied to the baby’s limbs and head and belly, enabling the team to capture the full range of movement.©2022 Kanazawa et al.

Based on the babies’ random exploratory activity, scientists discovered muscle interaction patterns that would enable the babies to perform sequential movements. Insight into how our sensorimotor system develops could offer insights into the origin of human movement and earlier diagnosis of developmental disorders.

Project Assistant Professor Hoshinori Kanazawa from the Graduate School of Information Science and Technology said, “Previous research into sensorimotor development has focused on kinematic properties, muscle activities which cause movement in a joint or a part of the body. However, our study focused on muscle activity and sensory input signals for the whole body. By combining a musculoskeletal model and neuroscientific method, we found that spontaneous movements, which seem to have no explicit task or purpose, contribute to coordinated sensorimotor development.”

Using motion capture technology, scientists recorded the joint movements of 12 healthy newborns (less than 10 days old) and ten young infants (about 3 months old). They then estimated the babies’ muscle activity and sensory input signals with the aid of a whole-body, infant-scale musculoskeletal computer model they had created.

Whole body simulation
Whole body simulation. This simulation was based on an adult model and infant skeleton. Credit: Kanazawa et al.

Last but not least, they employed computer methods to examine the spatiotemporal (both space-time) characteristics of the interaction between the input signals and muscle activity.

Kanazawa said“We were surprised that during spontaneous movement, infants’ movements “wandered” and they pursued various sensorimotor interactions. We named this phenomenon sensorimotor wandering. It has been commonly assumed that sensorimotor system development generally depends on repeated sensorimotor interactions, meaning the more you do the same action, the more likely you are to learn and remember it.”

“However, our results implied that infants develop their sensorimotor system based on explorational behavior or curiosity, so they are not just repeating the same action but a variety of actions. In addition, our findings provide a conceptual linkage between early spontaneous movements and neuronal activity.”

Combining data. Data from the motion capture was combined with the musculoskeletal computer simulation, which enabled the team to understand the flow of information along muscles and the babies’ perception of their movement.©2022 Kanazawa et al.

“The latest study’s results support the theory that newborns and infants can acquire sensorimotor modules, i.e., synchronized muscle activities and sensory inputs, through spontaneous whole-body movements without an explicit purpose or task.”

“Even though sensorimotor wandering, the babies showed an increase in coordinated whole-body movements and anticipatory movements. The movements performed by the infant group showed more common patterns and sequential movements, compared to the random movements of the newborn group.”

Journal Reference:

  1. Hoshinori Kanazawa, Yasunori Yamada, Kazutoshi Tanaka, Masahiko Kawai, Fusako Niwa, Kougoro Iwanaga, Yasuo Kuniyoshi, “Open-ended movements structure sensorimotor information in early human development,” The Proceedings of the National Academy of Sciences of the United States of America: December 26, 2022, DOI: 10.1073/pnas.2209953120


See stories of the future in your inbox each morning.