You’re a Dim Bulb (And I mean that in the best possible way)

By Carl Zimmer | March 23, 2006 4:56 pm

bulb150.jpgI have a fondness for collecting brain lore–memes about the wonders of the human brain that race around the world for decades. The classic of brain lore is the “ten-percent myth.” As I wrote here, people often claim we only use ten percent of our brain, implying that we’d be supergeniuses if we could just switch on the rest. But that’s just based on a misinterpretation of some studies in the 1930s. Actually, the energy consumed by the cortex is only enough to power one percent of its neurons at any time.

In a press release descibing the work of Stanford bioengineer Kwabena Boahen, I stumbled on another meme:

According to Boahen, the brain is capable of performing 10 quadrillion (that’s 10 to the 16th) “calculations,” or synaptic events, per second using only 10 watts of power. At this rate, he says, a computer as powerful as the human brain would require 1 gigawatt of power.

I searched for the origin of this meme, and discovered Paul Valery, an early 20th century poet and essayist. He declared:

The ultimate “computer,” our own brain, uses only ten watts of power — one-tenth the energy consumed by a hundred-watt bulb.

It’s a claim that falls in that gray zone, the intersection of cool and crazy. So to see if it was actually true, I asked Bill Leonard, an expert on the evolution of human brains at Northwestern University. He responded thusly:

This is really interesting. The 10 watt estimate looks pretty close to being correct — perhaps a bit on a the low side, but certainly in the ballpark.

In terms of calories, here is how the 10 watts translate:

10 watts = 10 joules/sec = 207 kcal/day for the brain

At 200-210 kcals, this is enough energy to support a brain of about 1000 grams, at the low end of the modern human range.

For an average size human brain — 1300 -1400 grams — the costs would be a bit higher — between 250-300 kcal/day. However, this would only up the “wattage” to about 15.

So there you go. One urban myth survives the cold scrutiny of reason! Pass it on in the full confidence that it’s true (not to mention amazing).

CATEGORIZED UNDER: Brains
MORE ABOUT: Brains

Comments (31)

Links to this Post

  1. Girls by Design: This is a Blog » Blog Archive » Fun Fact Friday: Mari edition | May 22, 2009
  2. 50 Incredibly Weird Facts About the Human Body | February 22, 2010
  3. 50 Incredibly Weird Facts About the Human Body | Health Care 4 Me | March 1, 2010
  4. 50 Incredibly Weird Facts About the Human Body | March 4, 2010
  5. 50 Incredibly Weird Facts About the Human Body | Tech News, Reviews, Business, Health News and More | March 19, 2010
  6. Fast fat burning tips » 50 Incredibly Weird Facts About the Human Body | June 2, 2010
  7. Thinking Tuesday « Esscentual Alchemy | September 28, 2010
  8. 50 Incredibly Weird Facts About the Human Body « Talesfromthelou's Blog | January 24, 2011
  9. 50 Incredibly Weird Facts About the Human Body « Just 4 Fun Pak | January 31, 2011
  10. Some Weird Facts About the Human Brain | May 21, 2011
  11. 50 Incredibly Weird Facts About the Human Body | Pakalert Press | June 26, 2011
  12. 2Health: How to take care of yourself. » Blog Archive » 50 Incredibly Weird Facts About the Human Body | July 6, 2011
  13. Take a gander at these crazy/cool facts about YOUR body! WHOA, BRO! « kkgalphagirls | September 21, 2011
  14. Robert JR Graham.com » 50 Incredibly Weird Facts About the Human Body | October 10, 2011
  15. 50 interesting facts about our body | don't worry, be happy. | November 5, 2011
  16. RWC Unfiltered 11-6-11 | Hypocrisy Reigns Supreme | November 6, 2011
  17. 50 Incredibly Weird Facts About the Human Body | ReadersNation.com | April 13, 2012
  18. 50 Incredibly Weird Facts About the Human Body « Ryaandavis | June 16, 2012
  1. You know what it’s called when more than 1% of the neurons in your brain fire at once? A seizure.

    Also, it’s really a mistake to equate synaptic events with calculations in a computer. Synaptic events are much, much simpler. When computer scientists talk about a “calculation”, they usually mean an amount of computation that takes one clock cycle, which might be to add two long numbers, or decide if one number is bigger or smaller than 0. To the extent we understand what computations synapses compute, they’re probably, at least mostly, small portions of an addition. The simplest model of a neuron basically computes “if the sum of the average firing rate of my input neurons is more than X, fire”. Any single synaptic event affecting that neuron is likely to be one of probably thousands of such events that is involved in that computation…

    On the other hand, 1% of the neurons in your brain can compute that kind of rule simultaneously, while your desktop computer can compute only one or two things at once.

  2. RPM

    Good work tracking that down. It looks like Albert Brooks may need to do a rewrite on Defending Your Life.

  3. This “We only use 10% (or 5% or 1% or whatever) of our brain” thing is mighty irritating. Of course we do. The brain is not homogenous; a given area is doing something pretty well defined. It’s not like you can take the fusiform gyrus when there is no faces to detect and temporarily help out with the algebra problem you’re working on.

    It’s like saying you only use 10% of your car at any one time just because you’re not using all gears at the same time, running both the heater and the air conditioner, and constantly opening and closing the doors, honking the horn and blinking the turn signals while weaving in lazy curves along the highway (so as not to waste the use of the steering wheel).

  4. josh

    “On the other hand, 1% of the neurons in your brain can compute that kind of rule simultaneously, while your desktop computer can compute only one or two things at once.”

    that isn’t quite true concerning computers. processor architecture and instruction sets have a lot to do with the number and type of operations per second. for example, dedicated graphics chips can process an immense number of graphic operations per second despite their relatively low clock rate. they suck at general computations though

  5. I noted a similar meme about a boy with no brain a while ago–add it to your collection, if it’s not already there.

  6. linklog 030626

    linklog 030626

  7. On the computer side, 10^16 IPS requires about 10^6 chips at about 100 Watts each, using desktop processors. 100 MegaWatts. If one uses processors that are designed for mobile devices, one gets better instruction per Watt rates – at least 10x but probably 100 times better. A Game Boy is one tenth the speed, but lasts 18 hours on a charge and doesn’t get hot. The other problem with these comparisions is that Moore’s Law tends to make the current answer obsolete so quickly.

    All that said, my experience is that through training, one can make the muscles perform to at least 800% better. Not all the gains are pure increased power – some is efficiency of use. There is plenty of evidence that the brain behaves similarly – though it may be more difficult to measure.

  8. luca

    Carl, you say: Actually, the energy consumed by the cortex is only enough to power one percent of its neurons at any time.

    Does this mean that were you to use more than that, your brain would drain the energy resources of your body too quickly? it may even overheat, I guess…

  9. Emily Sommer

    Thats awesome. I’ve always heard that statistic, but was always a bit doubtful. Very cool that tis true =)

  10. outeast

    So thinking really, really hard is a good way to lose weight?

  11. John

    I think a point that is missed here is that your neurons are “doing” something when they don’t fire, since it is the pattern and timing of neuronal firings that matters in thought (most likely). Adults are able to do many cognitive activities using far less energy than children doing the same activity (a more efficient mind will use less energy). So the myth is that more activity in your brain will equal better thought processes…

  12. Urban Living

    Religious people use ten percent of their brains.

  13. Qestion?

    Can the human form (only) exist in another dimension using 10-15watt?

    I believe they can but your input would be appreciated and be free to forward my email to those who have an opinion on the subject.

    Evrey body have a good day …..Ian

NEW ON DISCOVER
OPEN
CITIZEN SCIENCE
ADVERTISEMENT

Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!

The Loom

A blog about life, past and future. Written by DISCOVER contributing editor and columnist Carl Zimmer.

About Carl Zimmer

Carl Zimmer writes about science regularly for The New York Times and magazines such as DISCOVER, which also hosts his blog, The LoomHe is the author of 12 books, the most recent of which is Science Ink: Tattoos of the Science Obsessed.

ADVERTISEMENT

See More

ADVERTISEMENT
Collapse bottom bar
+

Login to your Account

X
E-mail address:
Password:
Remember me
Forgot your password?
No problem. Click here to have it e-mailed to you.

Not Registered Yet?

Register now for FREE. Registration only takes a few minutes to complete. Register now »