What do you think of this fact?
On the scale, your brain barely registers. On the energy bill, it is the biggest item in your whole body.
Small organ, big appetite
According to the Harvard Brain Science Initiative, the brain accounts for only 2 percent of your body weight but uses about 20 percent of your daily energy. EPFL in Lausanne gives the same ratio: roughly a fifth of the energy your body burns goes into keeping the brain running. Scientific American notes that this is more than any other organ uses.
And that is at rest. You don’t need to be solving a math problem for it. Even when you are just staring at the ceiling, your head is drawing its share.
Roughly a dim light bulb
How much power is that? The Physics Factbook, a collection of physics estimates, does the math: an average adult runs on about 100 watts, and 20 percent of that is about 20 watts. So everything you are thinking, seeing and remembering right now runs on the power of a fairly feeble lamp.
Where the energy goes
Scientific American describes a study that included radiologist Wei Chen of the University of Minnesota Medical School. The team used a scanning method called magnetic resonance spectroscopy to track ATP, the main energy molecule in cells. The result: about two-thirds of the brain’s energy goes into neurons firing and sending signals. The remaining third goes into what the article calls housekeeping, keeping the cells healthy.
So most of the budget is spent on the constant chatter between your nerve cells.
Bonus fact: In the same study, deeply anesthetized rats produced 50 percent fewer ATP molecules than lightly anesthetized ones.
Two percent of the mass, a fifth of the fuel: your most demanding roommate lives between your ears.