The resonant capacity of neurons
Wikipedia: Neural oscillations have been most widely studied in neural activity generated by large groups of neurons. Large-scale activity can be measured by techniques such as EEG. In general, EEG signals have a broad spectral content similar to pink noise, but also reveal oscillatory activity in specific frequency bands. The first discovered and best-known frequency band is alpha activity (7.5–12.5 Hz) that can be detected from the occipital lobe during relaxed wakefulness and which increases when the eyes are closed. Other frequency bands are: delta (1–4 Hz), theta (4–8 Hz), beta (13–30 Hz), low gamma (30–70 Hz), and high gamma (70–150 Hz) frequency bands, where faster rhythms such as gamma activity have been linked to cognitive processing. Indeed, EEG signals change dramatically during sleep and show a transition from faster frequencies to increasingly slower frequencies such as alpha waves. In fact, different sleep stages are commonly characterized by their spectral content. Consequently, neural oscillations have been linked to cognitive states, such as awareness and consciousness.
The ears: The Human sense for listening to air vibration, could detect frequency from 20 Hz to 20 000 kHz. But is this mean neurons being set to a rate detection about those limits?
Wikipedia: The cochlea of the inner ear, a marvel of physiological engineering, acts as both a frequency analyzer and nonlinear acoustic amplifier. The cochlea has over 32,000 hair cells. Outer hair cells primarily provide amplification of traveling waves that are induced by sound energy, while inner hair cells detect the motion of those waves and excite the (Type I) neurons of the auditory nerve.The basal end of the cochlea, where sounds enter from the middle ear, encodes the higher end of the audible frequency range while the apical end of the cochlea encodes the lower end of the frequency range. This tonotopy plays a crucial role in hearing, as it allows for spectral separation of sounds. A cross section of the cochlea will reveal an anatomical structure with three main chambers (scala vestibuli, scala media, and scala tympani). At the apical end of the cochlea, at an opening known as the helicotrema, the scala vestibuli merges with the scala tympani. The fluid found in these two cochlear chambers is perilymph, while scala media, or the cochlear duct, is filled with endolymph.
Wikipedia: Hair cells chronically leak Ca2+. This leakage causes a tonic release of neurotransmitter to the synapses. It is thought that this tonic release is what allows the hair cells to respond so quickly in response to mechanical stimuli. The quickness of the hair cell response may also be due to the fact that it can increase the amount of neurotransmitter release in response to a change as little as 100 μV in membrane potential.
We can see on the last drawing that the nature of the calcium-potasium system don't limit the frequency by itself, and can be improve by a factor of up to 20X and more, by a good configuration of the neurons cells, A good Brain Vs a little one: I'm an evil :)
Could we take the number of 20 000 Hz and multiply it by 100X ? This question arise, so let's consider building device, at first, that will be able to detect that range of frequency.
The eyes: The visible ligth spectrum, is from 400 nm to 700 nm, that mean 300 THz. It's a fact that neurons don't refresh at that speed. In the case of eye, the refresh is about 100 images per second. The cell emmit a impulse, not on every cycle of ligth input, but when they are hit directly and that this hit energy is producing an isomer in the retinal molecule. It looks like the pigments are only filter to this process, accepting the photon, and dissipating them in heat by an orbital change processing.
Wikipedia: The human retina contains about 120 million rod cells, and 6 million cone cells.