Sensory Experiences Build Neural Networks
Our sensory apparatus is so vital to learning that it begins developing within a couple of months after conception, in utero. We first learn about gravity through our vestibular system, even before birth. Hearing, smell, taste and touch build on our gravitational sense to give us our first images of the world. Only later are we able to put these increasing complex sensory images together to accommodate sight.
Nerve networks grow out of our unique sensory experiences, laying down intricate patterns that govern all our higher level brain development. Experience determines the shape and intricacy of these patterns. They are laid down in accordance with the activities we experience and all of our environmental circumstances. The richer our sensory environment and the greater our freedom to explore it, the more intricate will be the patterns for learning, thought and creativity.
Images derived from our sensory experience are the stuff of thought and creativity. Images- in the form of shapes, colors, movements, feelings, tones, spoken or unspoken words- arise from our acquired patterns throughout all areas of the brain: color and shape patterns from the occipital lobe, tones and words from the temporal and frontal lobes, emotional experiences from the limbic system, and movement patterns from the basal ganglion of the limbic system. When we hear the word truck, all our experiences with trucks are instantly available to us as images-- a heavier vehicle, noisy, dangerous, big wheels, diesel smell, sense of riding in one, how they feel as they pass us on the road, even the emotions of trucks as extensions of our power. From these images we make sense of new learning, tie remembered images together in different ways and come up with new ideas. Broad based knowledge depends on these intricately woven, yet separate multi-sensory complexes of images that have been put together and reworked over and over again from our sensory experiences.
Consider, for example, the way we learn and incorporate new words into our vocabulary. Each sound, word and phrase is supported by an elaborate internal image display. Whenever we read anything, the brain in actively putting the words into known sensory images so we may understand them. Notice that when you can't get an image of something you have read, it is difficult to determine the meaning.
Our sensory experiences, both external and internal, shape our way of imaging and, therefore, our thinking. New learning occurs as new sensory experiences modify, change and make ever more complex our images of our world and our selves. Our bodies are fully involved in this quest.
Developing Our Senses
In order to understand how essential sensory input is to learning, thought, and creativity, we must explore how the brain grows and matures, begining with its earliest structures and functions.
Dr. Paul MacLean, Chief of the Laboratory of Brain Evolution and Behavior at the National Institute of Mental Health in Washington, DC, developed a theory that postulates three district areas of the human brain. According to his Triune Brain Theory, the three parts are delineated biologically, electrically and chemically and are based on developmental patterns and evolved functioning. He named these three areas: 1) the reptilian brain, 2) the limbic or early mammalian brain, and 3) the neocortex or neo-mammalian brain.
The reptilian brain or brain stem is the first area to develop. This is the oldest evolutionary part of the brain, developing between conception and fifteen months after birth. The job of this brain is self preservation. The reptilian brain monitors the outer world through sensory input and then activates the body to physically respond in ways that ensure survival.
Automatic and reflex reactions such as a baby's cry or its quick movement of the leg away from pain, are partially regulated by this area of the brain. It is also the part of the brain which takes over when we encounter danger or stress, because it initiates and regulates the body's fight-or-flight response. The reptilian brain oversees the mond/body's survival imperative, insuring that basic needs are met before other, higher functions can proceed smoothly.
The baby's first job is to satisfy its need for food, warmth and shelter. So it learns to make appropriate responses that signal caretakers to provide for those needs. Eventually the baby learns-- through its sensory system-- enough about its world, and about how to work its body, to master its environment and ultimately provide for itself.
The reptilian brain includes the brain stem, medulla oblongata, pons and cerebellum. All sensations go first through the brain stem and then are sent on from the switch-board (the pons) to the thalamus (in the limbic brain) and/or the neocortex for interpreation. Nerve nets must be developed first in the reptilian brain. The rest of the brain can then know what is happening in the outer world and respond to it. When we gate (close down) the reptillian brain, we are in a state of sleep where we neither receive nor react with the outer world.
The reptilian brain forms nerve nets encoded with our sensory-motor base patterns upon which learning, all the rest of our lives, will build. Nerves appear three weeks after the egg is fertilized and immediately begin to link up with other nerves. These forming nerve nets originate from the billions of nerons in the central nervous system. As the reptilian brain forms, prenatally and in those first fifteen months of life, we develop an estimated 100 trillion nerve nets that link all our senses and muscle movements. These give us an understanding of the material world and our safety in it.
The Vestibular System: Sense of Motion and Equilibrium
When we think about our senses, most of the time we only consider the five senses that take in information from outside our bodies: seeing, hearing, smelling, tasting and touching. However, just as important to our development and our lives is the integration of sensory input which gives us information about gravity and motion, and about our body's muscular movements and postion in space-- vestibular system and proprioception. These play a surpisingly significant role in our awareness of the world and also, as we shall see, in our ability to understand and learn.
The first sensory system to fully develop and myelinate by five months after conception is the vestibular system, which controls the sense of movement and balance. This system maintains both static and dynamic equilibrium. Static equilibrium refers to the orientation of the body, mainly the head, relative to gravity, for example when you are standing still. Dynamic equilibrium maintains body position, mainly the head, in response to sudden movements such as acceleration, deceleration and rotation when you are in motion, as when walking.
There are several small organs involved in vestibular sensation. From them we gather information about the head's position relative to the ground. These are the most sensitive of all the sense organs, lying in the mastoid bone (the lump behind the ear lobe), and part of the inner ear. They include the utricle, saccule, semicircular canals, and vestibular nuclei of the medulla and pons.
The ultricle and saccle monitor the static equilibrium of the body. The walls of both the utricle and saccule contain the macula with hair cells, a gelatinous layer and otoliths (calcium carbonate crystals). Each time we move our heads the otoliths move, pulling the gelatinous layer, which pulls on the hair cells and makes them bend. The bending initiates sensory nerve impulses along the vestibular nerve to the brain. These impulses go through nerve tracts to the crebellum that monitors and makes corrective adjustments in the muscle activities, including eye movements, that orginate in the cerebral cortex. This causes the motor system to increase or decrease its impulses to specific muscles, especially the core (torso) and neck muscles, to contract or relax. In this way our muscles adjust instantly so we don't lose our balance or equilibrium.
With information from the utricle and saccule we are able to maintain a stable bodily posture relative to the ground. Travelling by car,air or water, however, can create a sense of disequilibrium which sometimes results in car, air or sea sickness.
Information from the eyes contributes to the sense of equilibrium as well. "About 20 percent of the messages from the eyes, from the retina and extraocular muscles," as Homer Hendrickson points out, "go to areas of the brain concerned with balance mechanisims. Each of these subsystems must match and check with the other subsystems to produce consistent static and dynamic balance against gravity.
Consider what happens when you read in a car. You are holding your eyes static as you read but the rest of your body is moving, especially the head. The system is having to work very hard to keep the eyes level and static in a moving head. At the same time it is attempting to balance the rest of the body with the constant change of gravity, acceleration and deceleration. When no resolution to the confusion occurs, the body vomits, which may be its way of getting our attention to release the eyes. A similar thing occurs in IMAX theaters where the eyes are having to move a lot, the body is static, and the communicatin between the two is confusing.
The three bony semicircular canals lie at approximately right angles to each other and maintain dynamic equilibrium by detecting imbalance in three planes. When the head moves due to rotation of the body, the endolymph fluid in the semicircular ducts flows over hair cells and bends them. Impulses from the bending hair cells follow the same pathways as those invovled in static equiilibrium.
According to Eugene Schwartz, even the slightest alteration of fluid and otolliths within the semicircle canals leads to changes in the muscles of the neck, trunk, limbs, and musculature of the eye. The vestibular system is already visible in a two month old embryo. There is much activation of the head as the fetus moves in the amniotic fluid, then as the child goes from early movements and crawling to walking and running. The stimulation from these movements is crucial to brain processing.
The vestibular nuclei, a plexus of neurons lying in the medulla oblongata and pons, carries impulses from the semicircular canals and cerebellum to the Reticular Activating System (RAS) in the brain stem. The RAS is a nerve reticulum that carries impules from the medulla oblongata and pons to the neocortex. Beginning in utero, the RAS "wakes up" the neocortex, increasing excitability and responsiveness to incoming sensory stimuli from the environment. This "wake up" by the RAS gets us ready to take in and respond to our environment, and to learn. This connection between the vestibular system and neocortex as well as the eyes and core muscles is highly important to the learning process. When we don't move and activate the vestibular system, we are not taking in information from the environment.
Children love to spin or ride for hours on hand pushed merry go rounds, activating the vestibular system. But have you noticed that as an adult you would prefer just to watch? There is a reason for this. As we go through puberty, the endolymph fluid in the semicircular canals thickens in response to reproductive hormones. This thickening causes the hair cells to be bent for a longer time, thus causing the whole system to take a longer time to return to a comfortable equilibrium.
Amusement parks and flight simulators that are designed to be sensory events have really capitalized on our vestibular systems. When they activate the vestibular system, the RAS wakes up the rest of the brain to the incoming stimuli. The rides then put the whole vestibular system off balance and out of equilibrium, causing not only a full body experience but also an adrenalin "high." Adrenalin, our survivial drug, allows for even more sensory input to the system in our attempt to perceive any danger in our environment. It gives the body a real, but not necessarily healthly workout.
From conception to the first fifteen months after birth, the vestibular system is very active as the child gains a sense of gravity and knowledge of the physical environment through movement. Every movement of the child stimulates the vestibular system, which stimulates the brain for new learning. From this sensory "wake up" and basal understanding of gravitiy a child is able to perfom the most remarkable feats of balance. Beginning with only reflexive movement at birth, the child learns to stand, walk and even run in a gravitational field by approxiamately one year of age. This initial learning allows us to walk on logs across streams, walk up stairs, ride bicycles, skate and millions of other things that require a strong sense of balance.
The Sense of Hearing
By twelve weeks, the fetus moves spontaneously. Nerves, lungs and diaphragm begin to synchornize, exercising the lungs for the first breath after birth. The fetus is surrounded by the first patterns of sounds that will be absorbed by the nervous system. These include the mother's heartbeat, her breathing, digestion and voice. At five months the fetus responds to phonemes of language (varying vibrations of sound such as the vowel sounds) that it hears through the amniotic fluid, spoken by the mother.
Using fiber optic cameras, Dr. Alfred Tomatis discovered that the fetus will move a specific muscle, in the arm or leg for example, when it hears a specific phoneme. The particular muscle moved varies in each fetus studied, but each time the same phoneme is sounded, the same muscle wil move. This early connection of a muscle response to sound suggests the significance of anchoring sensor input with action for learning to occur. There are approxiamately fifty phonemes in language world wide. This sensory-motor response to phonemes allows the fetus to begin the process of learning language in utero.
By twenty four weeks the fetus displays rapid eye movements during its sleeping time. The fetus responds to music by blinking its eyes and moving as though dancing to a beat. By the seventh month, the fetus is thought to exhibit purposeful movements that are more than just refective.
Cralle Physical Therapy and Hyperbaric Oxygen Delray Beach, Florida