Name: How fast is the speed of thought? - Seena Mathew
Uploaded: 2020-11-16T18:16:32.000Z
Duration: 5 min 16 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

Your mortal enemy has captured you and hooked you up to a bizarre experiment.

He's extended your nervous system  with one very long neuron

At some point,  he's going to fire an arrow.

If you can then think a thought  to the target before the arrow hits it,

In order to answer, we have to examine the hardware of thought: neurons.

The human brain has about 86 billion  of these cells.

They transmit signals down their axons  by way of electrical impulses,

One neuron can then pass that signal  to the next at a synapse

The signal is received  by the next neuron's dendrites,

propagated down its axon, and passed further along.

So, the key factors that determine  how quickly you think

include how long it takes to generate  an initial action potential;

propagate it down the length of the axon; and transport it through the synapse.

We must also factor in the number  of neurons involved

and the distance the signal has to travel.

Let's see what this looks like in a simple pathway— your knee-jerk reflex.

A strike to your patellar tendon  triggers an electrical impulse

that travels up a sensory neuron  to your spine.

There the signal branches,  and for the sake of simplicity,

we'll consider the segment that jumps into a motor neuron

The total length of the neurons  in that pathway

is about 1 meter in someone  who is 5 foot 5 inches,

and on average it takes  15 to 30 milliseconds from strike to kick.

so this signal travels somewhere  between 120 to 240 kilometers per hour.

The initial action potential accounts  for 1 to 5 milliseconds

and synaptic transmissions only take  .1 to .5 milliseconds,

so the bulk of that time is spent within the axons.

This is consistent with research findings

that the average individual neuron sends signals at around 180 kilometers per hour.

But speeds can be boosted with myelination and increased axon diameter.

Myelin is a fatty sheath  that insulates an axon,

preventing electrical currents from leaking out.

Meanwhile, axons with larger diameters offer less internal resistance.

These compounded factors can raise the speed of an action potential

There's plenty of variation:  some people think faster than others,

and your own speed of thought changes throughout your lifetime.

the myelin sheath covering your axons wears down,

Arrows shot from recurve bows fly, on average,

Which means that given a sufficiently long, myelinated or large-diameter neuron,

your thoughts actually could win the race.

The arrow and thought don't leave  the gate at the same time;

first the arrow fires,  then once you perceive it,

Processing images or music,  participating in inner speech,

and recalling memories all require complicated neural pathways

that are nowhere close to the linearity of the knee-jerk reflex.

The speed at which these thoughts occur is mostly consistent,

with variations based on myelination and axon diameter.

But the duration of a thought will vary significantly depending on its routes,

In this case, when you perceive a threatening stimulus,

a startle can be involuntary  and quite fast.

you might react  in less than 65 milliseconds.

More likely though, your startle reaction will be based on sight.

Our eyes can process an image  as quickly as 13 milliseconds,

but computation of what you're seeing and determining the danger it poses

can take as long  as 180 to 200 milliseconds.

In that time the arrow will have gained a head start of about 13 meters.

that you've got just enough  of a chance to catch up,

if you can quickly, and quite literally, think your way out.