The Nature and Nurture of Motor Development

“Once your baby has mastered his reaching abilities, he is taking his first step into exploring the physical world”

The rate in which your infant acquires his motor achievement has little relevance to his IQ score or any cognitive performance, as long as he lies in the normal range. Motor skills involve much more than just movement, these skills lead to an understanding of the social and physical environment. Once a baby masters his motor milestones, his experience will become broader and his perception of the world will drastically improve. Acquiring these skills comes in hand with a sense of independence, a higher self-esteem, stronger muscle growth and better coordination of neural circuits.

What motivates these developments? It was thought to be just nature’s job but it seems that nurture also plays a role as reinforcement. It is a combination of a programmed sequence of neural maturation and consistency in daily exercise. The neuromuscular maturation is indeed “hard wired” and its pace determines this progression. If there is no neuromuscular maturation then practice will not influence the development at all. The motor cortex is one of the first areas of the brain that shows electrical activity but it takes a while for it to fully mature.

Once your baby has mastered his reaching abilities, he is taking his first step into exploring the physical world. Grasping actually occurs before birth, though this is purely reflexive and it ends at 2 months. The babies enter into this phase called the fixed extension, which involves an extension of the arm but their fists tightly closed. Normally, successful reaching is achieved around the 4th month and by the 6th month; the act is smooth, accurate and very much controlled. How is this skill mastered? There is a blend of corticospinal fibers innervating the arms and muscles, motor cortical areas innervating the hand and myelination of fibers and vision that allows us to be able to accurately reach the target. Limbic and motor planning play a role here too, where experience gets to play a role in this achievement.

Walking equally impacts the baby’s cognition. He will experience a cognitive and social development once he masters this skill. However, the baby needs to have developed stability and strength. Walking involves the central pattern generator (CPG)—a network that triggers rhythmic muscular activity. The CPG matures really early, influencing the stepping reflex that involves a baby trying to take a step when held up vertically with the feet touching a flat surface. However, real walking requires a full mature nervous system. The brain areas controlling leg movements are essential, as well as sensory and motor systems that are involved in balance and posture. The growth of the baby’s proportion also provokes an easier balance. Practice is useful in walking because even though the spinal cord and CPG can produce a stepping pattern, the cortex decides when to start walking and so it adjusts the CPG to match the environment that this baby is trying to navigate. After walking is mastered, the first steps stabilize these corticospinal and other pathways in the brain that are needed for a smooth transition to walks resembling those of adults—practice accelerates this process! Studies suggest that those who exercise this milestone earlier than those who don’t tend to achieve this earlier. Practice strengthens the baby’s muscles and turns on the neural pathways.Thus, motor development is a blend between nature and nurture. Genes set the lower limit for when these skills can initiate their mastery, once the nervous system is set—practice strengthens these circuits, resulting in skilled and refined movements.
Eliot, L. (1999). What’s going on in there? How the brain and mind develop in the first five years of life, 237-239.

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