What is the neural code?

There has been a debate raging for as long as I can remember. Neurons fire in action potentials that seem stereotyped. Let's take the action potentials to be stereotyped for all practical purposes in reality. (Honestly, we should test this. We haven't quite tested this rigorously through mutual information calculations of, say, the mutual information between voltage time series relative to stimulus versus a point process encoding relative to stimulus. If the two are the same within error bars with a lot of data, the voltage itself provides no additional information basically about the stimulus compared to the spike itself.) We then must ask: what about the spikes carry the information?

Some said that the precise spike timing, exactly when the spikes occurred, determined the neural encoding of information. This code can contain quite a bit of information, if you just think about the entropy of a point process. This, however, is not a very robust code. Other people therefore proposed that firing rate-- the number of spikes over a larger time interval-- was a more robust code that could contain quite a bit of information. According to Izhikevich, who is a proponent of the spike timing hypothesis, firing rate might matter at the neuromuscular junction, but that's about it.

I think these debates ignore the fact that even though many neuroscience experiments involve presenting a static stimulus and then watching neurons respond, stimuli in real life are constantly fluctuating. Almost never do we see a movie that is static. In fact, our eye movements prohibit this by doing microsaccades all the time even if the image in front of us is static. As a result, we see constantly moving video no matter what, or we basically perceive nothing at all. So really, we are asking how to encode a constantly changing movie.

In reality, there is some dt on our perception. If you were to jitter that movie by just a bit, we wouldn't be able to perceive it. This is like when the fan goes too fast and it looks like it's continuous regardless of the speed past a certain point. So really, we have a discrete-time stimulus with a small dt that we constantly must encode.

The most natural code for that might actually be something that is neither based on spike timing or based on firing rate, really, but is effectively a binary vector. Basically, the neural response within a window of dt (the spike timing included) would be what encodes information. It seems like this could still allow for a firing rate code, but the refractory period prohibits multiple spikes in that window of dt, hence prohibiting a firing rate code for stimuli that must be constantly encoded. You could maybe see a spike timing code, but you have to weigh the amount of time it takes for an action potential to complete against the limits of sensory perception, this dt. In reality, dt depends on the sense being studied, and the correct calculation to this question might involve some understanding of the refractory period. This question might be incredibly complicated. But my money is on a binary vector not being such a bad representation of the actual neural code that is used in practice-- just, did each neuron spike or not. Thank goodness, because so many papers have used this neural code implicitly, including some of my own!

This question might be complicated a bit if a blocklength larger than 1 is used-- but that leads to time delays, which are quite costly for reinforcement learning reasons!