If we are more comfortable looking at the world through a lens of logic, balancing a checkbook, cutting a recipe in our heads by fifths, or performing any math skill, we might say we are left-brained.  And if we prefer the creative world, operate on intuition, and love music and art, we may consider ourselves right-brained.  But the truth is, we need both sides of our brains to do all of those things in our comfort zone.  We need the two sides of the brain to talk to each other in order to be truly successful at anything we do.

The two sides of the brain are divided by the corpus callosum.  A fully developed corpus callosum carries 4 billion messages per second between the right and left brain through 200 million nerve fibers.  This allows for complex thought to be manipulated into formal reasoning. Without that conversation and without stimulating that conversation, we are inhibiting the full operational value of the two hemispheres and the full functioning of reasoning.  In other words, the more we can access both sides of the brain, the more intelligently we operate in our world.

In order to fully access both sides of the brain, we must establish neural connections across the corpus callosum.  We do this by moving the appendages from one side of the body to the other side, across the midline. The midline is an invisible line that runs from the top of the head down to the ground, dividing the body into right and left sides.  The midline runs down the middle of the body from the tip of the head to the floor, dividing the body into right and left.

This imaginary line also runs along the corpus callosum, separating the two sides of the brain.  When we bring one body part across that midline into the space of the other part of the body, like crossing our legs or scratching an elbow, we are crossing the midline.  Crossing the midline is a skill that is developed with our first movement patterns, like rolling over, and should be fully developed by age 3 or 4.  It is further fortified in other skills and movement patterns developed along the way, like crawling and playing. The more freedom of movement a child is given, the more he is going to naturally develop his crossing-the-middle skills.

And the bonus is, the stronger the connection across the midline, the easier it is to process information.  Crossing the midline helps integrate the brain, helping children lay down critical neural pathways for attention, focus, behavior, academics, and more.  This simple motor movement helps establish a conversation across the corpus callosum and prevents the disconnection that leads to challenges and frustration.

Rolling over is a child’s first hefty crossing of the midline motor movement when they are infants, and it is followed by crawling, pulling up, and playing.  All of this activity allows the baby’s brain to move from one that is right-sided dominant, driven primarily by emotion and reaction, to one that begins to reason around age 3.  At this time, we begin to see the evolution of questions like “why” and ‘how,” which indicate more critical and complex thought brought on by the integration of the two sides of the brain.

Children start crossing the midline whenever they bring one hand across the body, whether in play or exploration, which can begin well before they are able to sit. They continue to develop it in crawling, then swimming, riding a bike, playing striking sports, doing cartwheels, and climbing, to name a few.  When the two sides of the brain do not communicate effectively, there is disintegration.

But the sooner we can allow significant physical movement, the better the chance of supporting right-left brain integration and a more robust interaction with the surrounding environment.

How do you strengthen it?

We strengthen this skill with use by actively bringing the appendages across the midline.  Some big body crossing the midline ideas are:

  • Crawling
  • Climbing
  • Monkey bars — hand over hand
  • Movement games with streamers or ribbons
  • March and try to touch the hand or the elbow to the opposite leg
  • Windmills
  • Wiping down a table or blackboard
  • Kicking a ball
  • Animal walking (crab, bear, puppy dog)
  • Marching like a toy soldier
  • Games like Twister or Simon Says
  • Yoga
  • Drawing big sideways figure 8s (infinity symbol) on a blackboard, in the sand, or with sidewalk chalk
  • Sweeping
  • Driving a “car” using a steering wheel (paper plate) and turning hard right and left
  • Sitting back to back with a friend and passing a ball from side to side to that friend

This all distills down to one critical message: motor movements are directly related to brain development.  When we remove physicality from a young child’s day, even with the best of intentions, we are inhibiting his ability to use his body not just to explore his world, but to organize and develop his brain for success.  As Maria Montessori said, “The hand is the instrument of the mind,” and her words speak volumes.