The Physics
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Power of a Human Brain

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Drubach, Daniel. The Brain Explained. New Jersey: Prentice-Hall, 2000. "Although the brain accounts for less than 2% of a person's weight, it consumes 20% of the body's energy." 20 W
"Body, Physics of." Macmillan Encyclopedia of Physics. New York: Macmillan, 1996. "The average power consumption of a typical adult is about 100 W." 20 W
Brown, Guy. The Energy of Life. New York: Free Press, 1999. "The human brain is only 2% of the weight of the body, but it consumes about 20% of the total energy in the body at rest." 20 W
Hart, Leslie. How the Brain Works. New York: Basic Books, Publishers, 1975. "Even so, the brain when awake demands a greedy share of the body's energy supply: thought weighing about 1/50 of the body total, it may use as much as 1/5 of all the energy that is consumed." 20 W
Yang, Eric. Think Dinner. Mac Evolution. 13 February 1998. "It's well known that the human brain accounts for about 20% of the total oxygen consumption when a person is at rest, so let us assume that the brain accounts for 20% of the total body energy consumption." 20 W

The brain makes up 2% of a person's weight. Despite this, even at rest, the brain consumes 20% of the body's energy. The brain consumes energy at 10 times the rate of the rest of the body per gram of tissue. The average power consumption of a typical adult is 100 Watts and the brain consumes 20% of this making the power of the brain 20 W.

Based on a 2400 calorie diet (Adapted from Yang)

2400 "food calorie" = 2400 kcal
2400 kcal/24 hr = 100 kcal/hr = 27.8 cal/sec = 116.38 J/s = 116 W
20% × 116 W = 23.3 W

Glucose is the main energy source for the brain. As the size and complexity of the brain increases, energy requirements increase.

The human brain is one of the most energy hungry organs in the body thereby increasing its vulnerability. If the energy supply is cut off for 10 minutes, there is permanent brain damage. There is no other organ nearly as sensitive to changes in its energy supply.

In 1955, Albert Einstein's brain was preserved for research. Three scientific papers have been published examining the features of Einstein's brain. Albert Einstein's brain differed to normal men's brain in that his brain had more glial cells per neuron that might indicate that neurons in Einstein's brain had an increased "metabolic need"-- they needed and used more energy. Einstein's brain weighed only 1,230 grams, which is less than the average adult male brain (about 1,400 grams). The thickness of Einstein's cerebral cortex was thinner. However, the density of neurons in Einstein's brain was greater. In other words, Einstein was able to pack more neurons in a given area of cortex.

The most recent study concerning Einstein's brain was published in the British medical journal The Lancet, on June 19, 1999. They found that a portion of the brain that governs mathematical abilities and spatial reasoning -- 2 key ingredients to the sort of thinking Einstein did best -- was 15% wider than average allowing better connection between its cells, which could have allowed them to work together more efficiently.

Jacqueline Ling -- 2001

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