There’s a long debate in neuroscience about whether information is encoded in timing of individual spikes or only their rates (where rate coding is a bit more similar to how ANNs work, but still different). It hasn’t been decided by any one paper, nor is it likely to be: it seems that different populations of neurons in different parts of the brain encode information through different means.
Not either-or. It is both. Spike rate variation is way too slow for some types of low level compute. Spike timing us critical for actions as “simple” as throwing a fast ball into the strike zone.
