5 Things You Didn’t Know About the Brain

Neuroscience dispelled myths and interesting facts about the brain.

Image Edited from Flickr

Without the constraints of a formal biology course and no responsibilities to actually learn anything in particular, it’s been great fun and rewarding to approach the subject with a beginner’s mind. Beginner’s mind. :)

Anyhow, this blog is the final article on the brain series, and attempts to answer some of the many dumb questions that I come up with as I was conducting this research:

  1. Exactly How Big and Complex is the Brain?
  2. Does Brain Size Matter?
  3. What Happens to the Brain as We Age?
  4. Can the Body Make New Brain Cells?
  5. How are Functions Represented in the Brain?

1. Exactly How Big and Complex is the Brain?

Here are some of the questions I had and some of the quick facts:

  • Weight of brain: ~3 pounds
  • Number of Cells in Brain: ~270B
  • Neurons in the brain: ~100B
  • Number of connections / synapses: ~100T
  • Average number of connections per neuron: ~1000
  • Largest node AI system: e.g. GPT-3 @ 185B (20% of brain)
  • Size of neuron: cell body (0.1mm), axon (nerve) can be 1.0m long
  • Number of neurotransmitter molecules working: Billions
  • Nerve speed: The fastest nerve cells carry messages at 120m/s (268mph)
  • Speed of pain: slow pain 2.0m/s, fast pain 20m/s (4.4–44mph)
  • Time to form a conscious thought: ~150ms
  • How much memory storage: Estimates range: ~2.5GB — 2.5Petabytes
  • Size of nervous system? Length of all nerves added up: 100,000 miles
  • Voltage of the Brain: 65mV
  • Energy used by the brain: 500 calories/day = 25% total calories/day
  • Time it would take to charge a smartphone with your brain: 70 hours

This infographic summarizes some of the key points nicely:

Interesting Brain Facts. Image Credit

2. Does Brain Size Matter?

Actually I assumed brain size didn’t matter so much (a sperm whale brain is 20 pounds!) but it seemed to me that having more neurons and corresponding brain complexity would be important. We add more neurons as we grow up => we get smarter, therefore more neurons => better and smarter.

And given that, it would make sense that humans with all our fancy higher level cognitive functions would have the most neurons of all animals. BUT it turns out that the African elephant has 3x as many neurons as a human.

Equally confusing, I assumed the cerebral cortex with all its fancy cognitive functions and that has 82% of the brain mass would have the most amount of neurons, BUT it turns out that the cerebral cortex has ~16B neurons (82% of brain mass), whereas the cerebellum has ~69B neurons and only 10% of the brain mass. Why does the cerebellum have 35x the neuron to brain mass density of the cerebral cortex?

It turns out that neither brain size or number of overall number of neurons matter — what matters is the purpose the system was designed for — or more accurately, evolved for. We see many animals with different size brains and different neural densities, but the neocortex in humans, for example, does have more brain density and number of neurons than in elephants, even though elephants have more neurons overall.

One speculation about the cerebral cortex and cerebellum neuron density mystery, is that the cerebellum evolved earlier, and the cerebral cortex evolved later, more efficiently and with a different more complex set of goals / outcomes. Simply a different, perhaps more efficient, architecture for a different task.

This paper shares research on exactly this topic examining the brain structure across a variety of mammals and conjectures that:

the cerebrum has a larger overall neuronal size … probably reflecting the importance of long-range connectivity through the subcortical white matter, while the cerebellum, mostly consists of short range connections with the gray matter.

This TED talk explains that humans are special because we have the greatest number of neurons of any animal in the cognitive cerebral cortex.

3. What Happens to the Brain as We Age?

What happens to cognitive function during aging? And how to keep the mind “sharp” as we age? Scientists don’t appear to have concrete answers to these questions, but it has been widely found that brain volume shrinks about 5% per decade after the age 40 and much faster after the age of 70. It is thought, but not confirmed, that this decline is a function of neuron cell death. The hippocampus, essential in the formation and retrieval of memories, in particular deteriorates with age. Additional factors are that hormones that protect and repair brain cells decline with age, and decreased blood flow to the brain impairs memory and cognitive skills.

Protective factors to reduce or slow brain decline include healthy lifestyle — including good diet, limited alcohol, active lifestyle/exercise, and intellectual pursuits. This TED talk — on how to live to be 100 — claims that having a strong “why” and a compelling purpose or reason to live is also correlated with a long fulfilling life.

4. Can the Body Make New Brain Cells?

This appears to be a hotly debated topic. The classic belief was that brain cells generate and develop during youth and adolescence and then cease to generate during adulthood. In modern times (say the last 10-20 years), that historical dogma had been over-turned and the new thinking was that neurogenesis — the adult generation of new neurons / brain cells — does take place. This of course is very encouraging and means that there may be ways to stimulate adult generation of brain cells and perhaps counter age related brain decline and diseases like Alzheimers. But then, even more recent research has challenged that challenger research. I’d say its safe to say scientists don’t know — but its far from definitive and neuroplasticity and neurogenesis remain exciting and important research topics.

5. How are Functions Represented in the Brain?

Iwas curious to know if each part of our human functionality was equally represented in the brain — you know a section for hearing, a section for vision, a section for craving tacos, etc. The short answer is no. While certain functions can be substantially represented in one area, the brain often uses multiple areas in tandem to accomplish functionalities. One fascinating finding and result of evolution, is that the brain has evolved to accomplish certain number of functions and in some cases may re-use the existing hardware to accomplish some different and new goals. One example is the use of the “disgust” capability of the insula or insular cortex. Historically disgust evolved to detect bad food and for food safety (e.g. that smells disgusting!). However, overtime the same neuroanatomy has evolved to trigger and light up for the perception of disgust on moral grounds. That is why certain types of adverse or immoral behavior give us that same feeling of disgust and make us want to take a shower or wash our hands. e.g. “Come out, damned spot!” -Lady MacBeth

Conclusion

This wraps-up the brain series and my first attempt at learning more about the brain and neuroscience. If you haven’t read the earlier articles, please feel free to check them out here.

I look forward to continuing to learn more about the neuroscience, cognitive science, psychology, and certainly applications of artificial intelligence and machine learning. Thanks in advance for your feedback, questions and suggestions for additional topics and places to learn more!

References:

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