And still all slow stuff, 4 to 12 Hz. There must be something in the brain that clocks faster, but nobody seems to have found it yet.
There's this thing called "scissor effect", where when you have two wavefronts colliding at an angle, you get an apparent wave that moves much faster than either of the input waves - if you do that with light, you can trivially exceed the speed of light. Now this isn't an information-carrying wave, but I believe you can still use this phenomenon as a "virtual clock", to synchronize a bunch of independent receivers to act on a frequency faster than the real, interfering clock signals.
Well, that, or the brain is just such a mess that it acts as a spread-spectrum source and none of the high frequencies are above the noise floor.
EDIT: and of course a little background research after writing this comment revealed it's already settled (through more invasive probing) that the human brain has elements operating in kilohertz range - the mystery isn't whether this happens, but how it adds up to cognition and consciousness.
It's not at all how humans build computational devices. But humans run digital signals at gigahertz rates and do intelligent design. Nature doesn't do either.
I suspect that there are numerous advantages to silicon computation that biological neurons can't touch, but the brain is no slouch either - it was optimized for millions of years to be good for what it does. It's very good at what it does - sometimes because of, and sometimes despite its architecture.
It's honestly amazing that the brain even works as well as it does, given how slow neurons are. I suspect that distributed population coding that seems to be endemic to neural networks can also serve as a workaround for neurons being unreliable, slow to recover and subject to fatigue.
But it isn’t. Every neuron runs the core circadian transcription-translation feedback oscillations. Every neuron is on a roughly 24 hour loop, synchronized by the master circadian oscillator, a clump of about 20k cells called the Suprachiasmatic nucleus.
The faster oscillations nest under that one, including the oscillations in firing rates.
Jet lag is when the synchrony and phase hierarchy breaks. Shift work does the same.
Now the brain doesn’t have a fast global clock like a chip. But that’s very much part of the evolutionary design. It’s not very energy efficient to have a fast global clock. And in a system like the brain, what purpose would it serve? In the brain, timing is information. You want the slow arrival of some signal to be slow so you can actually assign some meaning to it. A fast global clock would throw those gaps away.
In fact, there are neuromorphic and RACE logic chips that dump the global clock for the same efficiency reasons.
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.