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