February 27th, 2024
Written by: Catrina Hacker
Over the past several decades the world has seen unprecedented technological growth. The pocket-sized machines most of us carry around all day have replaced our cameras, calculators, and countless other pieces of technology. But even our marvelous smartphones appear flawed compared to the most complex and efficient piece of machinery you’ll encounter in your lifetime: your brain. And while your iPhone is likely to feel outdated in the next 5-10 years, it’s unlikely to catch up to the processing power of your brain any time soon. Let’s dive into some of the numbers that demonstrate just how amazing your brain is.
Speed
To understand just how quickly your brain works, tap your nose with your finger. While seemingly simple, your brain had to do a remarkable number of things to accomplish this that feel like they’re all happening instantaneously. Your brain had to process the photons of light coming from your device screen, identify that they are words, make sense of those words, send a message to your motor system that you want to move, and then send that message down to your hand with precise instructions about where and how to move. Your brain sends these messages by passing signals between neurons in and outside your brain. Those signals, called action potentials, can travel as fast as 150 meters per second (m/s)1!
To put that in perspective, the fastest of all land mammals, the cheetah, has a top speed of about 74.5 miles per hour (mph), which is just 33 m/s2. A commercial airplane must pass 335 mph before it can outrun your action potentials. And while it takes an airplane several minutes to hit that speed, your brain is sending millions of these speedy messages every minute.
Much of an action potential’s speed comes from a specialized fatty covering, called myelin, that is wrapped around the tails of neurons that need to send the fastest signals. Without myelin, action potentials travel between 0.5 and 10 m/s, closer to a Tour de France cyclist pushing through mountainous terrain3. However, action potentials rushing through myelinated neurons can reach the impressive speed of 150 m/s1.
Size
With all it can do, the average adult human brain weighs just 3 pounds4. That’s about the weight of a Macbook Air and even lighter than most standard laptops5. This remarkable organ that is central to everything we do and experience makes up only 2% of our body weight6! Packed into those 3 pounds are about 86 billion neurons and just as many non-neuronal cells7. That’s a whopping total of at least 172 billion cells in the brain. To illustrate just how big that number is, you would have to travel to the moon and back8 nearly 720,000 times or to the sun and back9 over 1,800 times to travel 172 billion miles. To get to this size, the brain must grow at a rate of 250,000 nerve cells per minute during the entire length of a pregnancy10.
With all those cells jammed into the brain, it’s remarkable that it fits in the confines of our skulls. One way the brain saves space is by folding the outer layers of brain tissue, called the neocortex, to jam a very large surface into a smaller space. Think of this like jamming a towel into a jar. If the towel can’t bend, the jar has to be big enough to hold the full unfolded towel, but if you can bend the towel to fit within the jar then you can fit it into a much smaller jar. This bending of the cortex is what causes the crinkly surface of the human brain, with the peaks of each fold called a gyrus and the low valleys between called a sulcus (Figure 1).
Energy Efficiency
Remarkable speed and size aside, what really sets the brain apart is its incredible energy efficiency. Despite making up just 2% of your body weight, the brain uses about 20% of your body’s oxygen and calories throughout the day6. Your brain needs a large portion of your body’s resources to keeps its billions of cells alive and active. However, all things considered, this is only enough energy to power a 100W light bulb (most incandescent light bulbs use about 60W)11.
Still not impressed? Let’s consider how much energy it takes to run modern artificial intelligence (AI) models like ChatGPT. While your brain could keep a room full of energy efficient light bulbs running in your home, one University of Washington researcher estimated that ChatGPT uses as much energy as 33,000 US households each day12. And despite some of the impressive things ChatGPT has accomplished, there’s no doubt that your brain is doing far more with far less energy. AI models are predicted to only continue growing in size. They have a lot to learn from the brain if they hope to become energy efficient.
A brain might be something everyone has, but it’s still an amazing organ worth celebrating. From its remarkable speed to its compact size and energy efficient power I predict it will be a while before any smartphone or AI model will be able to compare.
References
1. Purves, D. et al. Increased Conduction Velocity as a Result of Myelination. in Neuroscience. 2nd edition (Sinauer Associates, 2001).
2. WCS Wild View: The Cheetah’s Speed Limit. https://blog.wcs.org/photo/2020/10/08/the-cheetahs-speed-limit-africa/.
3. Stein, J. & blog, L. A. T. / F. the B. S. Think you’re Tour de France material? Probably not. Los Angeles Times https://www.latimes.com/health/la-xpm-2011-jul-21-la-heb-tour-de-france-20110721-story.html (2011).
4. Dekaban, A. S. & Sadowsky, D. Changes in brain weights during the span of human life: Relation of brain weights to body heights and body weights. Ann. Neurol. 4, 345–356 (1978).
5. MacBook Air 13- and 15-inch with M2 – Tech Specs. Apple https://www.apple.com/macbook-air-13-and-15-m2/specs/.
6. Raichle, M. E. & Gusnard, D. A. Appraising the brain’s energy budget. Proc. Natl. Acad. Sci. 99, 10237–10239 (2002).
7. Herculano-Houzel, S. The remarkable, yet not extraordinary, human brain as a scaled-up primate brain and its associated cost. Proc. Natl. Acad. Sci. 109, 10661–10668 (2012).
8. How far away is the Moon? | Royal Museums Greenwich. https://www.rmg.co.uk/stories/topics/how-far-away-moon.
9. Sohn, R. & updated, D. E. U. last. How Far is Earth from the Sun? Space.com https://www.space.com/17081-how-far-is-earth-from-the-sun.html (2022).
10. Ackerman, S. The Development and Shaping of the Brain. in Discovering the Brain (National Academies Press (US), 1992).
11. Kováč, L. The 20 W sleep‐walkers. EMBO Rep. 11, 2–2 (2010).
12. Q&A: UW researcher discusses just how much energy ChatGPT uses. UW News https://www.washington.edu/news/2023/07/27/how-much-energy-does-chatgpt-use/.
Figure 1 images from Gaetan Lee on Wikimedia Commons and Albert Kok on Wikimedia Commons.
Cover photo by Gerd Altmann from Pixabay.
PennNeuroKnow 
very good
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