The Out-of-Sync Child

by Carol Kranowitz

  “With occupational therapy, we began to overcome such hurdles as fear of movement and revulsion caused by unfamiliar textures. As his fear of new things diminished, as the world became a less scary place, transitions also improved. With a psychologist’s help, we structured the environment and managed behavioral responses (i.e., tantrums) consistently.

  “Gradually, our child has blossomed and we have learned to do something with him which I never thought would be possible. We learned to enjoy him. He is our favorite companion.

  “As I look back upon two years of OT and a nurturing nursery school, I shudder to think what a mess we would all have been without them. They were our lifeline, our hold on hope.

  “Here is my charge to you: If you have concerns about your own or another child, no matter how vague they seem or how inarticulate you feel verbalizing them, pursue them. A child can have less pronounced problems than mine and still need help. And in your pursuit, continue until you find hope. In doing so, you may free other wonderful, enjoyable, little people held hostage by sensory processing problems. They are too small and frightened to free themselves.”

  APPENDIX A: THE SENSORY PROCESSING MACHINE

  Here is a brief anatomy lesson about the central nervous system, and an explanation of how sensory processing occurs therein. This overview may help you appreciate the marvel of the brain-and-body connection.

  THE SYNCHRONIZED NERVOUS SYSTEM

  All animals respond to sensations of touch, movement and gravity, and body position. Thus, human animals share the hidden senses with goldfish and goats, falcons and frogs, caterpillars and clams. Through eons of evolution, humankind refined these senses in order to survive in a hazardous world.

  As life forms gradually arose from sea to land to treetops, they had to adapt to differing environments. Hands to pluck berries, limbs to climb trees, eyes to see moving as well as stationary objects, and ears to detect prey and predators developed over time.

  Along with these skills came increasingly complex sensations. The human brain evolved to process these sensations, so that the hand would pick a berry rather than a thorn, the limb would cling to a branch, the eye would discern a motionless tiger poised to pounce, and the ear would hear faraway hoof beats.

  With the most complex brain in the animal kingdom, humans have the most complex nervous system. Its main task is to process sensations.

  The nervous system has three main parts, working in harmony. One is the peripheral nervous system, running through organs and muscles, such as the eyes, ears, and limbs. The second part is the autonomic nervous system, controlling involuntary functions of heart rate, breathing, digestion, and reproduction. The third part is the central nervous system (CNS), consisting of countless neurons, a spinal cord, and a brain.

  THREE COMPONENTS OF THE CENTRAL NERVOUS SYSTEM

  A. The Neurons

  Neurons, or nerve cells, are the structural and functional units of the nervous system. Neurons tell us what is happening inside and outside our bodies. The brain has approximately 100 billion neurons. Each neuron has:

  • A cell body, with its nucleus inside.

  • Many short dendrites (Greek for “little branches”) reaching out to other neurons to receive messages, or impulses, and carrying them into the cell body.

  • A long axon, like a stem with roots, which sends impulses from the cell body to the dendrites of other neurons.

  A Neuron

  Two kinds of neurons connect the brain and spinal cord to the rest of the body: sensory and motor. Sensory neurons receive impulses from sensory receptors in our eyes, ears, skin, muscles, joints, and organs.

  Impulses travel along the sensory neuron’s axon and communicate messages to other neurons at contact points called synapses (Greek for “point of juncture”). Each neuron makes thousands of synaptic connections every time it fires. The neuron firing off the message is called presynaptic; the neuron receiving the message is called postsynaptic.

  At the nanosecond that the message is fired, neurotransmitters are released, causing an electrochemical response. When neurotransmitters activate the receptors of the postsynaptic neurons, they are called excitatory. When they do not activate receptors, they are called inhibitory. (The process of balancing excitatory and inhibitory messages is called modulation. See p. 57)

  The postsynaptic neurons may be other sensory neurons, or they may be motor neurons, the second kind of neurons in our CNS. Receiving the information, the motor neurons instruct muscles to move, glands to sweat, lungs to breathe, intestines to digest, and other body parts to respond appropriately.

  In the growing fetus, neurons and synaptic connections multiply rapidly. A baby is born with billions of neurons and trillions of synapses. Sensations of smell, touch, and hunger activate synaptic connections to help the baby survive. For instance, synaptic connections help him respond to a nipple so he can suck.

  To help the baby respond efficiently to this early skill of sucking, as well as to more complex skills, a process called myelination occurs. Myelin is a substance—somewhat like an electrical insulator—that coats the axon of the neuron to protect it, to smooth the path, and to speed up the connections.

  At about eighteen months, the child stops developing new neurons, because his brain already has all that it needs—and his skull has all that will fit! New synapses, however, keep multiplying as the child integrates new sensations. That is, synapses multiply if synaptic connections are useful for everyday functioning and if they are repeatedly used. Otherwise, they vanish.*

  By about twelve years, the child will lose many synapses he was born with, through a normal and necessary process called pruning. Pruning eliminates synapses the child does not need and stabilizes those he does. If he is Japanese, his brain will prune synapses necessary to pronounce the sound of “r,” because “r” isn’t used in his language. If he is French, his brain will strengthen these synapses, so he can roll an “r” with fluency.

  Normally, as the child actively responds to sensations, useful synaptic connections increase. The more connections, the more myelination; the more myelination, the stronger the neurological structure; and the stronger the neurological structure, the better equipped the child is to learn new skills.

  TWO EXAMPLES OF THE FUNCTION OF NEUROTRANSMITTERS

  City Sensations Become Routine

  You leave your quiet country home and visit the city for the first time. The sound of traffic, the sight of crowds, the smell of pollution, and the motion of escalators bombard your senses. Billions of neurons are firing messages; zillions of neurotransmitters are activating neuronal responses. Your nervous system is operating on overtime; that’s why you’re so “nervous”!

  After a few days, you begin to grow accustomed to city sensations. You no longer jump each time you hear screeching brakes or get jostled on the subway. Neurotransmitters now have less of an excitatory effect and more of an inhibitory effect. As your nervous system adapts to repeated stimuli, you can pay less attention to every sensation—and still survive.

  Painkillers Become Less Effective

  You have chronic back pain, so you take a painkiller. At first, the medicine helps as the neurotransmitters activate a response. After a while, the medicinal effect wears off because postsynaptic neurons have raised their threshold. Instead of just one painkiller to make you comfortable, you now require two or three.

  B. The Spinal Cord

  Extending below the brain is the spinal cord, a long, thick structure of nervous tissue. It receives all sensations from peripheral nerves in our skin and muscles and relays these messages up to the brain. The brain then interprets the sensory messages and sends motor messages back down to the spinal cord, which sends messages out to peripheral nerves in specific body parts.

  C. The Brain

  The human brain evolved over the course of 500 million years. Dr. Paul D. MacLean, brain researcher at the National Institute of Mental Health, has proposed that each human is born with a “triune brain.�
�� (This model of brain development is one of many. For our purposes, it is the simplest.)

  As we evolved, we added layers of brain material, each one improving earlier parts. The first layer is the reptilian complex: the “primitive brain.” It is responsible for reflexive, instinctive functions necessary for self-preservation and sexual drive. Sometimes these functions are called the “Four Fs”: Feeding, Fighting, Fleeing…and sexual reproduction.

  The Triune Brain

  The second layer is the limbic system (Latin for “border”). It is the “seat of emotions,” controlling hormones that enable us to feel angry, lustful, and jealous, as well as pleased and happy. Sometimes called the “smell brain,” this system processes smell and taste, which have a powerful effect on our emotions.

  The limbic system adds feelings to otherwise instinctive behavior. Thus, when we feel threatened, we fight or flee—or shut down. When we feel safe, we can play—and when we play, we can learn.

  The third layer is the cerebrum: the “thinking brain.” It is responsible for the organization of the most complex sensory intake. Detailed processing of sensations occurs here, so we can think, remember, make decisions, solve problems, plan and execute our actions, and communicate through language.

  FOUR BRAIN PARTS USED IN SENSORY PROCESSING

  Four important brain structures are involved in sensory processing. Let’s glance at them and see how they fit into the triune brain.

  1. The Brain Stem

  The brain stem, part of the “primitive brain,” is an extension of the spinal cord. The brain stem performs four key functions.

  • A crossroads, it receives sensory messages, particularly from skin and muscles in the head and neck, and relays this information to the cerebrum. In turn, the cerebrum sends out messages for motor coordination.

  • A switching gate, it is the location where sensations from the left side of the body cross over to the right cerebral hemisphere, and vice versa. It is here that outgoing responses from the left hemisphere instruct the right side of the body what to do, and vice versa.

  A Cross-Section of the Brain

  • A clearinghouse, it processes vestibular sensations necessary for hearing, maintaining our balance, seeing moving objects, and focusing our attention on one thing or another.

  • A regulator, it processes sensations from internal organs and controls breathing, heartbeat, and digestion. It is the seat of the reticular core, a neuronal network that exchanges data with the vestibular system to guide our sense of timing for waking up, falling asleep, getting excited, and calming down.

  2. The Cerebellum

  Another part of the primitive brain is the cerebellum (Latin for “little brain”). Processing proprioceptive and vestibular sensations, it coordinates muscle tone, balance, and all our body movements. It controls fine-motor skills, especially repetitive movements, such as touch-typing and practicing scales. It lets us move easily, precisely, and with good timing. An Olympic diver has a finely tuned cerebellum that allows him to execute a seemingly effortless dive.

  3. The Diencephalon

  The diencephalon (Greek for “divided brain”), sometimes called the “tweenbrain,” nestles in the center of the brain. A part of the limbic system, the diencephalon is associated with several important structures.

  The basal ganglia are clusters of nerves that coordinate vestibular sensations necessary for balance and voluntary movement. The basal ganglia relay messages among the inner ear, the cerebellum, and the cerebrum.

  The hippocampus (Greek for “sea horse,” which it resembles) compares old and new stimuli. If it remembers a sensation, like the feel of comfortable shoes, it sends out inhibitory neurons to tell the cortex not to get aroused. If the sensation is new, like too-tight boots, it alerts the cortex with excitatory neurons.

  The amygdala (Greek for “almond”) connects impulses from the olfactory system and the cortex. It processes emotional memories, such as the smell of an old boyfriend’s cologne, and influences emotional behavior, especially anger.

  The hypothalamus controls the autonomic nervous system, regulating temperature, water metabolism, reproduction, hunger and thirst, and our state of alertness. It also has centers for emotions: anger, fear, pain, and pleasure.

  The thalamus is the key relay station for processing all sensory data except smell. Thalamus means “couch” in Greek; it is where the cerebral hemispheres sit. Most sensations pass through it en route to our great gift, the cerebrum.

  4. The Cerebrum

  The most recently developed layer of the triune brain is the cerebrum (Latin for “brain”). Its wrinkled surface is the cerebral cortex (Latin for “bark”), often referred to as the neocortex because it is new, in evolutionary terms. The cerebrum is composed of two cerebral hemispheres.

  Why do we need two hemispheres? One theory is that the right and left hemispheres developed when early humanoids lived in trees and learned to use one hand independently from the other. This was a useful survival skill: One hand could gather fruit while the other clung to a branch. Asymmetric use of the hands and asymmetric hemispheres in the brain developed together in a process called lateralization (from Latin for “side”).

  With lateralization came specialization. Specialization describes the different jobs of the two hemispheres. With discrete duties, the right and left hemispheres must work together for us to function at a high level.

  In general, the left hemisphere is the cognitive side. It directs analytical, logical, and verbal tasks, such as doing math and using language. It controls the right side of the body, which is usually the action-oriented side.

  In general, the right hemisphere is the sensory, intuitive side. It directs nonverbal activities, such as recognizing faces, visualizing the shape of a pyramid, and responding to music. It controls the left side of the body.

  The corpus callosum (Latin for “hard-skinned body”), a bundle of billions of nerve fibers, connects the hemispheres. This neural highway carries messages back and forth, and integrates the memories, perceptions, and responses that each hemisphere processes separately. Thus, our right hemisphere creates an original thought or tune, and our left lets us write it down. Our right and left eyes look at someone and see a whole person, not two separate halves. Our right hand knows what our left hand is doing.

  FOUR MAJOR CORTICAL LOBES

  Each hemisphere has its own set of four major cortical lobes. Each lobe has a right side and a left side, both of which must work together, relaying neural messages back and forth, in order for the complex task of specialization to occur. The lobes have many administrative duties.

  The occipital lobes are for vision. They begin to process visual images before sending them to the parietal and temporal lobes for further interpretation.

  The parietal lobes are for body sense. They process proprioceptive messages, so we sense the position of our body in space, and tactile messages such as pain, temperature, and touch discrimination. These lobes interact with other brain parts to give the “whole picture.” For instance, they receive visual messages from the occipital lobes and integrate them with auditory and tactile messages, thus aiding vision and spatial awareness.

  Thr Left Hemisphere, Showing the Cortical Lobes, Sensory Cortex, and Motor Cortex

  The temporal lobes are for hearing, for interpreting music and language, for refining vestibular sensations, and for memory.

  The frontal lobes are for executive thinking. They have a motor area for organizing voluntary body movement, and a prefrontal area concerned with aspects of personality—speech, reasoning, remembering, self-control, problem solving, and planning ahead.

  THE SENSORY CORTEX AND THE MOTOR CORTEX

  Lying on the top are strips called the sensory cortex and motor cortex. The sensory cortex receives tactile and proprioceptive sensations from the body. The motor cortex sends messages through peripheral nerves to the muscles.

  In the early twentieth century, a Canadian neurosurgeon, Wilder Penfield, studied
these cortical areas to learn about neural functions. The “maps” below, based on his research, seem comically out of proportion. Their purpose is serious, however: to illustrate the relative importance of our body parts.

  Considerable portions of the sensory cortex are dedicated to receiving messages from the head and the hands—more than from the torso or arm, for instance. The reason is that body function is more important than body size; the head and hands have the most complex functions and thus produce the most sensations. Similarly large portions of the motor cortex are devoted to sending messages to direct the functions of the fingers, hands, tongue, and throat.

  Penfield’s Maps

  CEREBRAL HEMISPHERES MAKE US HUMAN

  Our cerebral hemispheres permit us to learn human skills, such as the ability to stand upright, thereby freeing our hands for manipulating and carrying objects. They enable us to speak, to reason, and to use symbols, thus enabling humankind to develop culture. They allow us to remember the past and to plan for the future, thereby increasing our chances for survival. They give us the mental tools not only to react but also to “pro-act,” that is, to anticipate what will happen next and to prepare an appropriate response. The locus of our finest movements and loftiest thoughts, they make us human.

  THREE EXAMPLES OF HOW THE CENTRAL NERVOUS SYSTEM PROCESSES SENSATIONS

  The Paper Cut

  Working at the copy machine, you get a paper cut on your finger. Tactile receptors in your skin send the message via myelinated sensory neurons through your peripheral nervous system to your brain: up your arm, through your spinal cord to your brain stem, to your thalamus, to the sensory cortex. The sensory cortex analyzes the message and tells neurotransmitters to fire excitatory impulses.

  First you become aware of the sense of light-touch pressure; a millisecond later, you are conscious of the tissue-damaging pain. Meanwhile, motor neurons send impulses to your finger. You say “Ouch!” and pull your finger away from the paper.