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Do We Really Use Only 10% of Our Brain?
- Written by Kenneth Wesson Kenneth Wesson
- Published: 28 March 2003 28 March 2003
As a possible spillover effect from the "Left-brained/Right-brained" craze, we often hear that human beings use only ten percent of our brains. The statement implies that we have already measured the brain’s maximum operational capabilities. There is not a single neuroscientist who has been able to quantify the brain’s full potential, which makes measuring ten per cent of an unknown quantity worthy of extreme suspicions.
What we do know is that there was a high physiological price to pay during cephalization, the evolutionary process by which neurons began to concentrate around the head region of primitive invertebrates. A higher level of cephalization developed in the more advanced invertebrates and later in the more complex brains of larger more sophisticated vertebrates like early hominids 3 million years ago. This process resulted in a considerably larger human brain (and cranium in which to house it).
An unavoidable consequence of the new talents in humans to use language and tools, and for living in complex social arrangements, was the cortical expansion of the human brain. These new developments accompanied bipedal mobility. Unfortunately, upright walking (bipedalism) had its downside for the women. It caused the human female’s hips to grow narrower to support walking in an upright position. As the hips contracted, the birth canal grew narrower. Had the reverse conditions prevailed -- the human head getting smaller as the dimensions of the birth canal increased---the challenge of childbirth would be largely absent. Instead, a larger cranium was required to pass through a slowly constricting birth canal. The evolutionary "correction" for this dilemma was to compel a greater portion of human brain development to take place in the postnatal periods unlike most other mammals that are "geared to go" only hours after birth.
Thus, human beings are among the most helpless creatures on earth immediately following birth. Twelve to fourteen years must pass before a human being can satisfactorily care for himself and function independent of his parents. Most parents of teenagers and young adults might take issue with the figures of 12-14 years, considering those to be wildly optimistic numbers, since the parental "time investment" for contemporary offspring has been greatly extended. The sustained care for our children, in many contemporary cases, seems endless.
While the brain competed with other organs in the body for a high position in the functional pecking order over the past 4-5 million years, the brain’s volume crept up to a 350% increase in size (originally 400 cc.) The human brain consequently became an extremely "high maintenance" organ (see figure 4). When body weights are plotted against brain weight, animals with large brains are quite rare. brain an evolutionary luxury that continued to consume vast amounts of resources (nutrients, energy and oxygen) unchecked by the omnipresent monitoring systems? Evolutionary processes are not known for their compassion and generosity. Instead, they operate by the more rigid use-it-or-lose-it principle. From an evolutionary standpoint, a brain that is used only 10% of the time (and therefore useless during the other 90%) would never be tolerated over a lengthy time span of ongoing evolutionary scrutiny, assessments and adjustments ("corrections").
Figure 4- Brain Statistics
The weight of the human brain (average) = 3 pounds (1300 - 1400 gm.)
Relative weight of the neocortex at birth = (12 ounces/350 g.) 25% of its adult weight
Weight of the cortex at 6 months = 50% of its adult weight *
Weight of the cortex at 30 months = 75% of its adult weight
Cerebral cortex at age 5 (before school) = 90% of its adult weight
Percent of total body weight that the brain represents = 2% (avg.)
Percent of body’s oxygen consumed by the brain = 25%
Percent of body’s glucose burned up by the brain = 70% Average
Percent of body’s nutrients consumed by the brain = 25%
Number of neurons in the brain= 100 billion
Cerebral blood flow = 1.5 pints traverse through the brain every minute
Miles of blood vessels capillaries and other transport systems in the brain = 100,000 miles
Number of connections in the adult brain = 1 quadrillion (one million billion)
Percentage of the brain’s total volume constituted by the cerebral cortex = 25%
Percentage of the brain’s neurons housed by the cerebral cortex = 80-85%
Thickness of cerebral cortex = 1.5 - 4.5 mm. or 1/8 inch (the thickness of a dime)
Number of cortical layers in the brain = Six
*During the first 6 months of life, there is a massive increase in the weight of the developing young brain due to the myelination of the axons, along with the tremendous increase in the number of dendrites and glial cells. These events combine to generate a 1-milligram/minute growth rate in the young brain.
New brain-imaging evidence would dismiss the notion that only 10% of the human brain is only used at any given time. In PET (Positron Emission Tomography) scans for any activity including sleeping, the entire brain "lights up" in nearly every area indicating a great amount of cortical activity taking place during the execution of nearly all cognitive tasks. More than 60% of the brain is active even during REM (Rapid Eye Movement) sleep or dreaming.
In cases of brain disease and trauma, we only wish that 90% of the brain had been held in reserve, which would guarantee the restoration of brain functioning following events such as strokes, missile wounds, or automobile accidents. No one yet has demonstrated that he or she could function well after losing 90% of his or her brain. To the contrary, there is no known region of the human brain that can endure even low levels of damage without extensive loss in mental capacity or major functional changes evidenced by one’s behavior. Recovering all of an individual’s premorbid (before injury) or pre-operative abilities almost never occurs.
Early Egyptians were so baffled by what the human brain actually did that they relegated it to a minor functional role. So minor was their perception of the brain’s job that the heart, kidneys, lungs, and liver were preserved along with mummified bodies, but not the brain, since its value was questionable at best. Some neuroscientists have traced the "10% legend" back to the early neuroanatomists who were only able to identify approximately 10% of what the various parts of the brain actually did, which lead others to infer that only ten percent of the brain was functioning. Since, only 10% of the brain had been mapped and account for, many concluded that only that amount was ever subject to being utilized.
The important questions are:
1. How much of the brain’s capacity do we use?
2. Can we develop a brain to its full potential?
3. What can be done in a classroom to maximize the development of a young brain?
4. How can keep an adult brain performing at its highest levels for an entire lifetime?
At this point in time, no definitive or conclusive credible answers are available.