The human brain requires a highly stable temperature and a supply of high
protein and energy. Evolutionarily speaking, it is a very expensive organ to
maintain. Fully one quarter of our caloric intake is used by the brain, which
comprises only 2% of our total body mass.
In the United States, the average caloric consumption is 3600 Kcal per
person daily. (You’ll note that this is approximately 1000 Kcal over the
recommended daily amount.) The kilocalorie (Kcal) is a unit of heat, equal to
1000 calories. It’s important to know that a nutritionist’s calorie is
different from a physicist’s calorie. A nutritionist’s calorie is equal
to 1 Kcal. What you see printed on food labels or in diet books are
nutritionist’s calories. I don’t know who originated this confusing
disconnect in scientific terminology -- but whoever he was, I hope he’s
getting his "just desserts" now in the netherworld.
Heat is convertible to energy, which is most often expressed as Joules. So
1 kilocalorie (or 1 nutritionist’s calorie) is equal to 4,186 Joules. A
kilocalorie is the amount of heat required to raise the temperature of 1
kilogram of water by 1°C at 1 atmosphere pressure. Converting an average U.S.
citizen’s consumption of 3600 Kcal of food per day into energy terms yields
15,070 kilojoules of energy.
It sounds like a lot, but it’s not. If this amount of energy were used to
heat water, it could in principle bring 10 gallons to a boil (starting from 10oC).
Or it could heat up a very small (25 gallon) water heater to the required
household temperature (50oC). Expressed in alternate energy terms,
our bodies are consuming a little over 4 kilowatt-hours per day, with the
brain taking 1 kilowatt-hour of that total for its own purposes.
If we were able to get all our required energy by simply plugging ourselves
into an electrical socket, it would only cost us about $0.40/day to survive.
That’s roughly equivalent to keeping a 175W incandescent light bulb burning
all the time. So if you’re "having a thought", the little light bulb hovering
over your head is only a 40W one -- pretty dim, at best.
PET and MRI studies have shown that brain energy consumption rises and
fails with emotional swings, learning new tasks, and rest vs. active status.
Surprisingly though, these changes are small in relation to the constant
"background" brain energy usage – as little as 10% of the total. It’s
interesting that the balance of brain energy even in an awake, resting and
unstimulated state is devoted to the very same neurotransmission signaling
duties as are the small percentages of energy added by challenging tasks or
"hard thinking". To explain this,
some scientists hypothesize that our brains are constantly engaged in
maintaining a "probabilistic model" of anticipated events and are, therefore,
not heavily dependent on sensory information at all!
Why am I suddenly thinking of that classic old Sci-Fi movie, "Donovan’s
Brain"? That was the one with the functioning, conversing brain in a tank.
After having calculated the relatively low wattage produced by the human
body, it also makes me question the credibility of the story-line of "The
Matrix", wherein humans are kept alive in tanks in order to harvest their
energy. You wouldn’t really be able to maintain much of a civilization using
such poor "organic batteries". For example, in 1998, the total
U.S. daily energy consumption was 260 trillion BTUs, or 75 billion
kilowatt-hours. You’d have to harvest the total energy from 19 billion humans to fulfill
that energy demand. At
last count, there were only about 6.5 billion people in the world. So this
premise is not very plausible at all – although there are a few people out
there that I would dearly love to throw in a tank and attach electrodes to.
(Michael Jackson comes to mind rather quickly…)
Back to Lost Articles...
See also Lyris Autran & Kathryn Blair’s article in
Neurology Reviews, Vol. 9 No. 2, Feb. 2001.
Quite recently, researchers at Panasonic's Nanotechnology Research
Laboratory in Japan have developed a way to draw power from blood glucose --
mimicking the way the body produces energy from food. The result could be a
device capable of producing electricity from blood, effectively turning bodies
into "human batteries". See
here.
And for all my fellow Mystery Science Theater 3000 fans,
here are the lyrics
to that great song, "When I held Your Brain in My Arms"...
