Well you could assign an approximate Hz for the brain by looking at how fast a single neuron can fire, around 500Hz [0]. But this is wrong in two ways. While one neuron is "reloading", another could fire, as they operate out of synch. But also, one pulse from one neuron doesn't really convey that much information. It takes more than that to send a message. You could also look at brainwaves or say flicker fusion thresholds, which gives a value in the double digits.
An action potential is a discrete thing that either happens or doesn't happen. This is the dominant mode of neurotransmission. But yeah I do believe there are some other possibilities too, but they are less important.
[0] https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5067378/