Babies make many different movements in the womb and immediately after birth. These seem random and uncoordinated, but are the basis for developing purposeful movements. This is shown by a study that combined detailed motion capture recordings of newborns and infants with a computer model of the musculoskeletal system. Accordingly, the babies' muscle interactions show patterns that become more complex as the baby grows older and are important for the maturation of the sensorimotor system. The findings could also help to diagnose developmental disorders at an early stage.
On the one hand, when we move, our brain sends instructions to our muscles on how to contract or relax, so that we are able, for example, to raise our arm or grasp an object. On the other hand, signals also go in the other direction: Sensory receptors in our muscles, tendons and joints send information to our brain, giving feedback about their movement and position. Even without looking, we know where our limbs are at all times. However, this body awareness, known as proprioception, only develops over time. Babies must therefore first learn to control their limbs in a targeted manner and to integrate the information reported back.
Motion capture for newborns
A team led by Hoshinori Kanazawa from the University of Tokyo in Japan has now investigated how the spontaneous, uncoordinated movements observed in babies contribute to the children later being able to move in a targeted manner. "Previous research on sensorimotor development has focused on kinematic properties, which are muscle activities that cause movement in a joint or body part," explains Kanazawa. "However, our study focused on muscle activity and sensory inputs for the whole body."
The research team equipped twelve newborns less than ten days old and ten infants three months old with markers for motion capture recordings, recording their movements. They combined the data with a full-body model of the babies' musculoskeletal system, which allowed them to estimate muscle activity and the sensory input signals underlying the observed movements. With the help of computer algorithms, they analyzed how sensors and muscle activity interact spatially and temporally.
Self-organization through spontaneous movements
“We were surprised to find that the infants' movements 'wandered' during spontaneous movement and that they followed different sensorimotor interactions. We've dubbed this phenomenon 'sensorimotor wandering,'" says Kanazawa. Until now, scientists have assumed that the sensorimotor system develops through repeated sensorimotor interactions. Accordingly, one learns a course of action the better, the more often one executes it. "However, our results suggest that infants develop their own sensorimotor system based on exploratory behavior or curiosity, meaning that they do not just repeat the same action, but a variety of actions," reports Kanazawa.
"While these early movements are not goal-directed, they provide specific regularities in the bidirectional information between muscle activity and proprioception," the authors explain. The movement analyzes showed that the complexity of the movements increased between the ages of ten days and three months. The researchers discovered more frequent patterns and sequential movements in the three-month-old infants - a step on the way to developing coordinated movements. "Our results show that early movements contribute to sensorimotor development in a self-organizing way," the researchers said.
Further studies planned
In future studies, Kanazawa and his team want to investigate how sensorimotor walking affects later development, for example when children learn to walk and grasp. According to the researchers, insights into early motor development can also help to diagnose developmental disorders at an early stage and specifically support infants with corresponding needs.
Source: Hoshinori Kanazawa (University of Tokyo, Japan) et al., Proceedings of the National Academy of Sciences, doi: 10.1073/pnas.2209953120