Mystery of why babies kick in the womb solved by scientists

The mystery of why babies kick in the womb has finally been solved by scientists who say it helps their development.

Apparently random movements boost development of the sensorimotor system – such as hand-eye co-ordination, according to new research.

Right from birth – and even before – infants start to kick, wiggle and move seemingly without aim or external stimulation.

A kick can carry a force of more than 10lbs and has mystified scientists for centuries. Now a model shows it helps the infant learn to control its body.

The discovery has implications for medical conditions and developing more agile machines.

A Japanese team combined detailed motion capture of newborns and infants with a musculoskeletal computer model. It enabled them to analyse communication among muscles and sensation across the whole body.

They found patterns of muscle interaction developing based on the babies’ random exploratory behaviour. It later helped them to perform sequential movements.

The discovery has implications for medical conditions. It sheds fresh light on a host of disorders. They range from cramps and spasms to multiple sclerosis, spinal cord injury, motor neurone disease and even cerebral palsy.

The hundreds of neurons that control each muscle are synchronised in the foetus to create strong contractions that activate ‘sensors’. Better understanding of the sensorimotor system develops could lead to earlier diagnoses – and more effective treatments. Currently, there is limited knowledge about how babies learn to move their body.

Dr Hoshinori Kanazawa, of the University of Tokyo and a co-author of the study, 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 spontaneous movements, which seem to have no explicit task or purpose, contribute to coordinated sensorimotor development.’

The findings are based on recordings of the joint movements of 12 healthy newborns less than 10 days old and 10 young infants aged about three months.

Muscle activity and sensory input signals were estimated using the infant-scale musculoskeletal computer model of the whole body.

Computer algorithms to analysed space and time, or ‘spatiotemporal’, features of the interactions.

Dr Kanazawa added: ‘We were surprised during spontaneous movement, infants’ movements ‘wandered’ and they pursued various sensorimotor interactions.

‘We named this phenomenon ‘sensorimotor wandering’. It has been commonly assumed 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 infants develop their own sensorimotor system based on explorational behaviour or curiosity, 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 behaviour involves a small set of primitive muscular control patterns. They can typically be seen in task-specific or cyclic movements, like walking or reaching.

The latest results support the theory newborns and infants can acquire coordination skills through spontaneous whole-body movements without an explicit purpose or task. Even through ‘sensorimotor wandering’, the babies showed an increase in coordinated whole-body and anticipatory movements. Infants showed more common patterns and sequential movements, compared to the random movements of the newborn group.

Prof Kanazawa is now planning to look at how sensorimotor wandering affects later development, such as walking and reaching, along with more complex behaviours and higher cognitive functions.

He added: ‘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.’

Most pregnant women begin to feel their baby move between 16 and 24 weeks and the movements can be described as anything from a kick, flutter, swish or roll.

The study is published in Proceedings of the National Academy of Sciences.

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