Gamma waves go up to 100 Hz. High gamma and ripples measured deeper in the brain during memory consolidation can briefly fire up to 200 Hz.

But speed isn’t all that useful, here. Neuronal activity is slow, but you can cancel it out, and control it mid firing. You have subdendritic and sub-axonal processing, so you can shoot off a signal, then tamp it down as it’s traveling, or ramp it up for some stretches of your axon, etc. Getting message fastest from cell A to cell B isn’t what we’ve needed. Rather, you get rich information that can have all kinds of impacts on cells along the way.