Origins Of Touch: Developmental Neurobiology
Human embryos begin life as a flat disk with three distinct layers of embryonic cells: endoderm, mesoderm and ectoderm. The endoderm, the innermost layer, ultimately produces the lining of the internal organs. The connective tissues, muscles and vascular system are derived from the mesoderm, the middle layer. The genesis of the nervous system — the brain and spinal column — and the skin is in the outermost layer, the ectoderm.
Before birth, an extensive web of touch receptors traverses throughout the developing fetal body. The actual sense of touch begins to emerge after only two weeks in utero, at which time sensations to the fetal lips and nose start to register for the first time. The spinothalmic nerve tract, which detects touch and pain, is among those sensory systems that develop at the earliest prenatal developmental stages.
All children extract their greatest amount of environmental knowledge by means of firsthand sensory experiences. From the eighth to the 36th month of life, there are more brain connections (synaptic proliferation) forming in the brain than at any other period in one’s lifetime. The young brain is primed to receive a flurry of sensory input from the senses, which aid perceptions as the child adapts to the outside world. A caress, a kiss, an affectionate pat on the buttocks or a pin-prick in the same region all instantaneously set in motion responses from specialized nerve receptors.
Once they begin to crawl, infants and toddlers embark on daily excursions into their new world, investigating anything they can see, touch, grasp, pick up and taste, usually in that precise order. Object manipulation helps young children make sense of the tangible world and lays the foundations required for success in abstract thinking later. These experiences are critical to concept formation in the mind’s eye — ideas that can be mentally manipulated in multiple contexts, both simple and complex.
Scores of tactile experiences activate the amygdala, which adds an emotional dimension to our tactile memories. Neuroscientists at the University of Southern California have discovered that when you look at an object, your brain not only processes what the object looks like but remembers what the object feels like when touching it. Feelings such as warmth and safety or repulsion and fear become inextricably associated with the words cotton, blanket, thorny, etc., divulging precisely how we “feel” about encountering each of them. Eventually, the entire world becomes represented by our past sensory experiences. Human brains capture and store physical sensations and replay them when prompted by viewing a corresponding visual image.
Our intimate familiarity with a loved one involves his or her appearance, smell, the way s/he feels, the sound of the voice, and his/her kiss, all of which collectively separates that individual distinctively from any other. All significant parties to the sensory experience must be accounted for. With ease, we capture the color, shape, smell, and texture of a lemon, but when interrupted by the strong scent of an onion we instantly cancel the preconception of lemon.
Humans have evolved the ability to accommodate a symphony of relevant sensory inputs simultaneously. When we hear a loud noise behind us, we turn to see what caused the noise. The visual, auditory, and association cortices attempt to make sense of the clamor. Vision becomes symbiotic and additive, rather than separate to hearing, by appending another dimension to the experience.
Researcher Dr. James Shymansky and his colleagues found that approximately 13 percent of all K-12 students are auditory learners, over 90 percent of American academic instruction is delivered through textbooks, reading materials, and lectures nearly 95 percent of the time. However, most early learning is self-initiated learning that comes by way of multimodal firsthand explorations, which are the keys to long-term cognitive development. Expanding the number of classroom opportunities where children can exploit the incredible power of their senses will generate deeper learning results and higher levels of student achievement.
Steps for Investigating Brain-Sight
Try this. You will need an assortment of small objects or toy models, one sheet of graph paper, a pencil and a partner:
- Partner A folds a sheet of graph paper into quadrants and closes his/her eyes until instructed to open them.
- Partner B gives Partner A an object.
- Drawing #1: With eyes remaining closed, Partner A touches, feels, examines, explores, and visualizes the object with both hands.
- Once Partner A feels confident enough to draw the object, Partner A returns the object to Partner B, who places it where Partner A cannot see it.
- Partner A is now invited to open his/her eyes and draw the object, starting his/her drawing in the first quadrant of the graph paper. The drawing must be based exclusively on the tactile information derived from the sensory experience — not memory. Partner A may examine the object additional times, if necessary, but only with his/her eyes closed.
- When Partner A has finished the drawing, he/she can look at the object and compare it to his/her brain-sight drawing.
- Drawing #2: Partner A now places the object on the table and looks at the object while drawing it in the second quadrant of the graph paper, with the advantage of seeing it this time as he/she draws.
- Drawing #3: On the same piece of graph paper, Partner A now traces the object in the third quadrant.
- Compare the first two drawings. Which is a more accurate representation of the object?
- Compare all three drawings. Which is the most accurate representation of the object? Which is the second best rendition of the object?
This article was first published in Brain World Magazine’s Spring 2012 issue.
