Why do neurons fire at a maximum of about 200 Hz?

Neuroscientist Paul King weighs in via Quora:

There are different ways of answering this question.

In terms of evolution, the answer would have to do with the so-called “metabolic budget” of the brain. The oxygen and glucose consumption of the brain, which is already 20% of the total for the body, cannot support an average firing rate of much above 10 Hz. If you assume some “expressive range” centered at a mean of 10 Hz, the low end might be around 1 Hz or less, and the high couldn’t be much above 100 Hz assuming a logarithmic distribution. One could argue that much above 100 Hz, the individual spikes start to become “wasted”; that is, the expressive power of each additional spike is minimal when several spikes have already happened in succession from the same neuron relative to that same spike coming from a different neuron. But this is a “just so” story that can’t really be tested.

Mechanistically, there are limits to how fast the whole neuron can generate and propagate a spike. The speeds are determined by how long it takes the receptors and ion channels to complete a whole voltage activate-deactivate cycle. The metabolics of the neuron are tuned for the average rate, which means that very high rates cannot be sustained without depleting the neuron, then it needs time to recharge (to reset the sodium and potassium ion gradients using ATP-powered ion pumps). The refractory period would be the major factor here, with bursting neurons having (I believe) special mechanisms for temporarily overcoming the refractory period.

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anonymous neuroscientist says:

June 17, 2017 at 12:07 am

I have a few comments about this answer incorporating research from 2010, if you don’t mind.

>The metabolics of the neuron are tuned for the average rate, which means that very high rates cannot be sustained without depleting the neuron

This is not correct. Neurons which have a high firing rate are tuned to that rate, at moderate extra metabolic cost. Each action potential takes more energy than otherwise, even if the neuron is not firing rapidly, so it’s only beneficial for neurons who’s operation requires high frequency spike trains or tonal activity. Neurons which only need to fire slowly or infrequently are tuned to that slower speed, using techniques that maximize energy efficiency at that speed. These neurons have wide action potentials and their kinetics prevent them from firing at a high rate.

>The refractory period would be the major factor here, with bursting neurons having (I believe) special mechanisms for temporarily overcoming the refractory period.

It’s not that the refractory period is overcome, it’s that neurons with a high firing rate have a narrower action potential due to overlapping the sodium-mediated depolarization and potassium-mediated hyperpolarization. This is accomplished by an increase in the number of quickly-activating delayed-rectifier channels (gene KCNC1). There is an increased energy cost due to the overlapping, so cells which do not have a high firing rate tend to have more slowly-activating potassium channels, in addition to more quickly-activating sodium channels to help offset the metabolic cost.

There is a paper about this (“Metabolic cost as a unifying principle governing neuronal biophysics”): http://www.pnas.org/content/107/27/12329.full

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Why do neurons fire at a maximum of about 200 Hz?