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Human brain cells can pass chemical information to each other at a speed just slightly above 400km/h, which is quite fast. However, this has to be multiplied by every cell needed to make a single thought.

Plus, the reaction and process time of every cell involved has to be summed up which, in the end makes us think relatively slowly - at least in my opinion.

So what would a brain require to be faster - how and why?

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    $\begingroup$ This is a huge topic. If you and I were to go grab drinks, I could probably talk to you about it for a few days straight, maybe stopping for eating and bathroom breaks. The limitations of our brain are actually less based on signal transmission than you may think, because our brains are not organized like a computer. We actually think in a totally different way which elides the signal speed issues rather well. The limit of your speed of thinking is actually based on how fast you can develop a consensus, not just neural transmission speed. There's a lot of things we could do... $\endgroup$
    – Cort Ammon
    Jul 8 '16 at 1:47
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    $\begingroup$ ... to increase signal velocity which would actually slow our brain down because they would negatively impact our ability to do the incredible parallel processing and analog processing that our brain does so well. $\endgroup$
    – Cort Ammon
    Jul 8 '16 at 1:48
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    $\begingroup$ My favorite example: If you are walkking with your eyes closed, and you bump into something with your right hand, not only does your brain react before you are fully aware of it, but in fact your body adjusts the gait of your left foot to compensate before the signal has even propagated up to the brain! Our spinal column does a lot more processing than we might think! Likewise, the patellar reflex is a monosynaptic reflex arc - we actually connect the stress sensor directly to the motor neurons that cause us to kick when our knee is tapped. It's a beautiful system! $\endgroup$
    – Cort Ammon
    Jul 8 '16 at 1:49
  • $\begingroup$ Well, you could make everybody else slower, I guess. $\endgroup$
    – Jason C
    Jul 8 '16 at 3:37
  • $\begingroup$ Chemical signals at 400km/h? As far as I know that's about the speed of the electrical signals passing through neuron fibres, and chemical signals are much slower. $\endgroup$
    – Vim
    Jul 8 '16 at 4:37
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There are likely a lot of things you could do. I'll pick two of them.

  1. Add more myelin to axons. An action potential - also commonly called a "nerve impulse" - can be made to travel faster by adding more myelin to an axon, the part of a neuron that carries electrical signals. For axons with myelin, the velocity $v$ of a signal varies linearly with the diameter $d$, whereas for axons without myelin, $v$ varies with $\sqrt{d}$:

    Comparison of conduction velocity in myelinated and unmyelinated neurons
    Image courtesy of Wikipedia user WillowW under the the Creative Commons Attribution 3.0 Unported license.

  2. Use more electrical synapses, rather than chemical synapses. Synapses help carry signals between neurons. Chemical synapses use neurotransmitters to carry the transmission, whereas electrical synapses don't. This greatly increase transmission speeds in some animals. However, they aren't used in many parts of the human brain. Use them all over and you can likely greatly improve transmission speeds. You'll have to devote more brainpower to gathering resources, though; electrical synapses are more energy expensive.

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    $\begingroup$ The reason that brains have chemical synapses is that building and maintaining the chemical signalling system is cheap (in terms of resources), whereas building & maintaining the electrical system is expensive. IIRC especially keeping the electrical synapse at an action potential ready to fire. So basically you brain was built by the lowest bidder! More electrical synapses is possible, but the payoff has to be bigger than the cost. So that faster thinking is mostly going to be dedicated to getting more food to fuel it OR to having more babies to out-compete the slow thinkers. $\endgroup$
    – DrBob
    Jul 8 '16 at 11:08
  • $\begingroup$ @DrBob That's interesting. I didn't know that. $\endgroup$
    – HDE 226868
    Jul 8 '16 at 13:48
  • $\begingroup$ I only found that out at a lecture by a neurobiologist at an animal behaviour conference a couple of years back. Annoyingly, I can't remember her name! $\endgroup$
    – DrBob
    Jul 8 '16 at 19:18