THE BODY MANDALA
Maps, Maps, Everywhere
If you were asked, “Does your hand belong to you?” you would naturally
say, “Of course.”
But ask neuroscientists the same question and they will turn the
question back on you: How do you know it’s your own hand? In fact, how
do you know that you have a body? What makes you think you own it? How
do you know where your body begins and ends? How do you keep track of
its position in space?
Try this little exercise: Imagine there is a straight line running down
the middle of your body, dividing it into a left half and a right half.
Using your right hand, pat different parts of your body on the right
side—cheek, shoulder, hip, thigh, knee, foot. With your finger, trace a
line over your right eyebrow and over the right portions of your upper
and lower lips.
You are able to tell these body parts from one another because each is
faithfully mapped in a two-dimensional swath of neural tissue in your
left brain that specializes in touch. The same thing goes for the left
side of your body: All its parts are mapped in a similar region of your
right brain. Your brain maintains a complete map of your body’s
surface, with patches devoted to each finger, hand, cheek, lip,
eyebrow, shoulder, hip, knee, and all the rest.
A map can be defined as any scheme that spells out one-to-one
correspondences between two different things. In a road map, any given
point on the map corresponds to some location in the larger world, and
each adjacent point on the map represents an adjacent real-world
location. The same holds broadly true for the body maps in your brain.
Aspects of the outside world and the body’s anatomy are systematically
mapped onto brain tissue. Thus the topology, or spatial relationships,
of your body’s surface is preserved in your touch map to a high degree:
The foot map is next to the shin map, which is next to the thigh map,
which is next to the hip map. Whenever someone claps you on the
shoulder, nerve cells in the shoulder region in this map are activated.
When you kick a soccer ball, the corresponding part of your foot map is
activated. When you scratch your elbow, both your elbow region and
fingertip regions are activated. This map is your primary physical
window on the world around you, the entry point for all the raw touch
information streaming moment by moment into your brain.
This touch information is collected by special receptors throughout
your body, funneled into your spinal cord, and sent up to your brain
along two major pathways. The more ancient of these pathways carries
pain, temperature, itch, tickle, sexual sensation, crude
to know that you bumped your knee and not your shin, but not acute
enough to tell a penny from a dime—and sensual touch, which includes
the gentle maternal caresses that were vital for your body map
development as a baby.
The evolutionarily newer pathway carries fine touch information—the
kind you need in order to thread a needle or leaf through a book—and
position- and-location information from receptors embedded in your
joints, bones, and muscles.
Once these many channels of sensory information reach your brain, they
are combined to create complex, composite sensations such as wetness,
hairiness, fleshiness, and rubberiness. The same goes for the many
varieties of pain. Through a combination of pain- and touch-related
signals, you have access to the rich diversity of unpleasant experience
that includes the smarting pain of a sunburn, the shooting pain of
carpal tunnel syndrome, the piercing pain of a stab wound, the dull
throbbing pain of an abused knee, the itchy pain of healing, and so on.
You also have a primary motor map in your brain for making movements.
Instead of receiving inputs from your skin, this map sends output
signals to your muscles. Just like the touch map, this movement map is
also found in both sides of the brain. It is vital to your ability to
guide your body parts to make fine-tuned movements and assume complex
positions in space—like doing the hokey-pokey, playing hockey, or
assuming a poker face in a high stakes card game. When you wiggle all
your toes, the toe and foot regions of your motor map are active. When
you stick out your tongue, the map’s tongue and jaw regions are active.
Thanks to this map, all the low-level, mostly unconscious tasks of
coordinated movement unfold smoothly without a glitch.
Elsewhere in your brain you also have a very different but no less
critical body map of all your body’s innards. This is your primary
visceral map, a patchwork of small neural swatches that represent your
heart, lungs, liver, colon, rectum, stomach, and all your various other
giblets. This map is uniquely super-developed in the human species, and
it gives you a level of access to the ebb and flow of your internal
sensations unequaled anywhere else in the animal kingdom. You feel
lust, disgust, sadness, joy, shame, and humiliation as a result of this
body mapping. These visceral inputs to the psyche are the wellspring of
the rich and vivid emotional awareness that few other creatures even
come close to enjoying. The activity in this map is the voice of your
conscience, the thrill of music, the foundation of the emotionally
nuanced and morally sensitive self. ###
from The Body
Has a Mind of Its Own by Sandra Blakeslee and
Matthew Blakeslee Copyright © 2007 by Sandra Blakeslee. Excerpted by
permission of Random House Trade Paperbacks, a division of Random
House, Inc. All rights reserved. No part of this excerpt may be
reproduced or reprinted without permission in writing from the