The changes in what an infant can physically do, the course of motor development in early life, is a source of constant and profound amazement.  We all begin life unable to walk, talk, grab,or even smile.  But, within a few short months, our newborns learn to smile, grab, sit, and walk.  Unless some neurologic problem intervenes, every baby born goes through this sequence, in that order, and all in less than a year and half.

In this note, we take a look at that sequence- smile, grab, sit, and walk- and see what the fact this is the order implies.  

One of the striking aspects of that sequence is that it goes from the top of the baby to the bottom of the baby’s body.  Smiling takes place only on the face, walking requires the feet.  It goes literally from head to toe.  Why is that?

This move from head to toe reveals that gaining these new skills reflects an astounding sequence in which the cerebral cortex takes over the functioning of the body’s muscles.   The cerebral cortex is a thin layer of nerves, about six business cards thick, that manage all the motions, thoughts, and feelings of our lives.  It contains about 100 billion neurons or nerves, each connected to about 10,000 others.  At birth, none of the muscles of the body are connected or controlled by this thin sheet of neurons.  We say none of the muscles are under cortical control.

Cortical control involves special sheathing of the nerves of the cortex to take place so that information moves rapidly enough for control and ease of management to occur.  Those sheaths are made of myelin, and the process of myelin being laid down is called myelination.  Once sheathed, the nerve signal shoots down the nerve many times faster, and once information flashes more quickly, more complicated actions become possible, like walking.

And so, the reason development goes from head to toe is that myelination physically proceeds from head to toe.   One can trace the progress just by looking at your baby.   When the cortex gets control of the muscles of the face, complex facial gestures in response to complex events begin to occur- that is, your newborn can now smile playfully and with love.   As the cortex gains controls of the muscles of the shoulders, arms and hands you can grab purposively.   With cortical control of the back muscles comes sitting, and of the legs and feet, walking.

Two developmental steps not mentioned are also part of this sequence, but not always:  rolling over and crawling.   Rolling over involves shoulder and back muscles and always happens, when it does, after smiling, around the time of grabbing, around 3-4 months of age.  A fairly large number of babies never roll over, maybe as many as 1/4-1/3.  Skipping rolling over causes no harm and is not associated with any later trouble with development.  It truly is an elective, not a required course.

The other elective step is crawling.  More infants crawl than roll over, but not everyone.  In the case of crawling, it is most often skipped in the context of an infant choosing to walk rather than crawl.  Again, skipping crawling causes no harm, and is not associated with any later trouble with development.  It truly is an elective, not a required course, too.   When it does take place, it also is always part of the head to toe sequence of motor development.  It always comes after sitting and before walking, and involves cortical control of the leg muscles.

One more note on the electives, rolling over and crawling.  There is a false idea that remains oddly popular about development.  That is, rolling over and crawling are not elective, they are required, and if they are skipped that can cause serious malfunctions later in life.  It has been proposed that if either are skipped, children will be left with impaired thinking and social skills.   And, further, that if one forces the child later in life to replay the developmental sequence, this time with rolling over and crawling, they will recover their impaired functions.  None of this is true.  Skipping rolling over and/or crawling, as already noted, has no impact on anyone.  Forcing someone to crawl when they do not want to offers no benefit, only anger.

So as we watch our newborns develop the incredible abilities to smile, grab, sit, and walk, enjoy knowing that we are watching our babies’ brains develop, their cortical wiring getting upgraded.  Most incredibly, we are watching our babies’ imaginative cortical mind take over the operations of their muscles.  From that point on, our muscles now reflect the imagination, purpose, and potential of our minds.

Dr. Arthur Lavin

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