Your Brain Uses the Same Power as a 20-Watt Light Bulb

Your brain weighs about 3 pounds — roughly 2% of your body weight. But it consumes about 20% of your body's total energy, using roughly 20 watts of power. That's the same as a dim light bulb, and it's running constantly, even when you sleep. In fact, your brain is almost as active during sleep as when you're awake, busy consolidating memories and clearing metabolic waste.

What makes this remarkable is the comparison with computers. The world's fastest supercomputers require megawatts of power to perform tasks that your brain does casually. IBM's Watson, which won Jeopardy!, required about 85,000 watts. Your brain, doing everything from recognizing faces to understanding sarcasm to keeping your heart beating, manages on 4,000 times less power.

But this efficiency comes with a vulnerability: your brain has almost no energy reserves. It depends on a constant supply of glucose and oxygen from your blood. Cut off blood flow for just 5-6 minutes and irreversible damage begins. Your brain is the most energy-efficient supercomputer on Earth, but it runs on a razor-thin margin.