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

Understanding these voluntary movements and their involvement in early human development may help identify early indicators of certain developmental disorders, such as cerebral palsy.

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

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

Based on the babies’ random exploratory activity, scientists discovered muscle interaction patterns that would allow the babies to perform sequential movements. Understanding how our sensorimotor system develops can provide insight into the origins of human movement and early diagnosis of developmental disorders.

Graduate School of Information Science and Technology Project Assistant Professor Hoshinori Kanazawa said: “Previous research on sensorimotor development has focused on kinematic properties, muscle activities that cause movement in a joint or part of the body. However, our research focused on muscle activity and sensory input signals for the whole body. By combining a musculoskeletal model and a neuroscientific method, we found that spontaneous movements, which appear 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 10 infants (about 3 months old). They then estimated the babies’ muscle activity and sensory input signals using a computer model of the baby-scale musculoskeletal system they created for the whole body.

Full body simulation
Full body simulation. This simulation was based on an adult model and a baby skeleton. Credit: Kanazawa et al.

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

Kanazawa said, “We were surprised that during spontaneous movements, babies’ movements ‘wandered off’ and emulated different sensorimotor interactions. We called this phenomenon sensorimotor wandering. It is generally believed that the development of the sensorimotor system generally depends on repeated sensorimotor interactions, meaning that the more times you perform 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 exploratory behavior or curiosity, so they repeat not just the same action, but a variety of actions. In addition, our findings provide a conceptual link between early spontaneous movements and neuronal activity.”

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

“The results of the latest study 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 goal or task.”

“Although sensorimotor wandering, the babies showed an increase in full-body coordinated movements and anticipatory movements. The movements of the infant group showed more generalized patterns and sequential movements, compared to the random movements of the newborn group.”

Magazine 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 United States National Academy of Sciences of America: December 26, 2022, DOI: 10.1073/pnas.2209953120