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Baby movements seem random, but help with coordination

Young babies never lie still. They move continuously, giving kicks and wriggles, and reaching out with their arms. Right from birth – and even in the womb – babies start to make movements that are seemingly random and have no purpose. New research conducted by scientists from the University of Tokyo, Japan, has now found that these “spontaneous movements” have an important role in the development of the sensorimotor system that enables us to control our muscles, movements and coordination.

Whole-body coordination involves large-scale sensorimotor interaction, and the ability to make the desired movements. When these bodily movements are made in the early stages of a baby’s life, they may potentially help the baby acquire this complex coordinated behavior. It is as though the baby is practicing this behavior and, thereby, preparing his or her muscles and joints, as well as stimulating neuronal development.

Currently, there is limited knowledge about how newborns and infants learn to move their bodies in a coordinated fashion. “Previous research into sensorimotor development has focused on kinematic properties, muscle activities which cause movement in a joint or a part of the body,” said Project Assistant Professor Hoshinori Kanazawa from the Graduate School of Information Science and Technology. “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.”

For their study, the researchers recruited 12 healthy neonates (< 10 days old) and 10 young infants of around 3 months in age. None of them or their first-degree relatives had neurological impairments. The team recorded the joint movements of the babies in the absence of external stimulation for 60 s, while they were awake, active and in a happy state. In addition, they recorded the three-dimensional positions of 51 markers on the muscles and joints of the babies, using 12 infrared cameras. 

The researchers then placed a set of three markers to define the relative positions of each body link connected through the joint. The target joints were the shoulder, elbow, hand, hip, knee, and ankle. The body links connected through the joints included the head, trunk, upper arm, forearm, hand, pelvis, thigh, calf, and foot. In this way, they mapped the exact movements of these elements.

The babies’ muscle activity and sensory input signals were estimated with the help of a whole-body, infant-scale musculoskeletal computer model which had been developed by the researchers. Finally, they used computer algorithms to analyze the ways in which the input signals and muscle activity interacted, spatially and temporally, during the babies’ open-ended movements. 

The results of the study, published in the Proceedings of the National Academy of Sciences, showed that the spontaneous, whole-body movements that neonates and infants exhibit could contribute to the structure of sensorimotor interactions, such as walking or reaching for something, later in life. Even though the movements appear to have no pattern or purpose, and are akin to “sensorimotor wandering,” they could contribute to the self-organizing sensorimotor interactions in the future. It was as though the movements are a form of practicing for the future and are certainly not simply random.

“We were surprised that during spontaneous movement, infants’ movements “wandered” and they pursued various sensorimotor interactions. We named this phenomenon ‘sensorimotor wandering,’” said Kanazawa. “It has been commonly assumed that sensorimotor system development generally depends on the occurrence of 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 own sensorimotor system based on explorational behavior or curiosity,” he continued, “so they are not just repeating the same action but a variety of actions. In addition to this, our findings provide a conceptual linkage between early spontaneous movements and spontaneous neuronal activity.”

Previous studies on humans and animals have shown that motor behavior (movement) involves a small set of primitive muscular control patterns. These are patterns that can typically be seen in task-specific or cyclic movements, like walking or reaching. The results of this latest study supports 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. 

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

The researchers believe that a better understanding of these movements and their role in later functions, will help us to understand how they are involved in early human development. We may also be able to identify early indicators of certain developmental disorders, such as cerebral palsy. 

Next, Kanazawa wants to look at how sensorimotor wandering affects later development, such as walking and reaching, along with more complex behaviors and higher cognitive functions. “My original background is in infant rehabilitation. My big goal through my research is to understand the underlying mechanisms of early motor development and to find knowledge that will help to promote baby development.”

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By Alison Bosman, Staff Writer

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