Phew, you dug more than enough for me thanks alot!
The picture that answers even more than I asked for is in the wikipedia page you linked: https://upload.wikimedia.org/wikipedia/commons/4/4a/Action_potential.svg
That’s a great picture because even though it looks like an average image of a “typical” neuron, who made it put a real effort to plot it in milliseconds by millivolts. I’m pretty sure the proportions are accurate.
There is entirely clear that:
- a neuron has a lower bound limit of ~5ms between consecutive firings, which is consistent with the upper limit of 200hz firing rate.
- which means a single synapse cannot fire faster than every 5ms = the upper rate of its upstream neuron.
- and from the same chart those pesky “Failed initiations” bumps in activation potential are smaller than 1ms
- Also I would assume the smaller bump is a single synapse fire, while the double sized bump is produced be two synapses firing very close to each other.
Hence the “firing opportunity” for one synapse is sparsely occurring less than 5% of the times within a pulse train of e.g. 50Hz of a single synapse
What leads to the idea of neurons talking with each other in “chirps” rather than single spikes.
What does that mean exactly? A chirp is (received as) a train of <1ms short bumps in action potential - the train can be shorter or longer and can have bumps closer or farther apart (== higher or lower frequency)
Let’s consider only two input synapses with overlapping chirps - one chirps at an average 100 hz another at 120hz - so bumps from both overlap at no more than 20 times / sec rate.
But 2 overlaps is not sufficient to reach activation potential, it requires both more nearby synapses to chirp too, and the chance of overlapping 3-5 bumps in order to reach activation potential increases with frequency of each individual synapse and with number of synapses chirping together.
When more synapses chirp “louder” together the receiving neuron chirps itself “louder”.
This is a very different perspective from that of binary on/off individual pulse encodings.
Furthermore see this very nice neuron firing footage from Subutai’s presentation: https://youtu.be/LbZtc_zWBS4?t=307
Initially I thought that each “flash” is a single neuron activation spike and the film is slowed down so we can have time to notice on-off short spike of each neuron, but now I would bet those firings are shown in real time and each neuron pulse there are “chirps” of dozens of ms length, and the brighter the “firing” means the stronger (higher frequency) chirp is.
What is also amazing is the noticeable rhythm each neuron has, the flashes repeat with regularities, and we can see different neurons with similar but slightly different rythms.
Because what applies to overlapping individual spikes could also apply to overlapping of chirps. Overlapping of slightly different “rhythms” on receiving synapses could produce a different rhythm of chirping with a specific strength for the receiving neuron.
That could explain our attraction for both sound and geometric patterns - flowers, mandalas, geometric tiles and music. We don’t usually eat flowers, why are we fascinated by them?
Maybe because they trigger meaning/correlations without any underlying conditioning derived from the hard coded priors/needs for food, safety or water.
They just correlate with the underlying functioning of the brain.
PS and the “pleasure” they produce is simply because brain rewards itself for noticing a new, unexpected pattern