I've always found Retinal Waves[1] interesting. During development of the visual system, there are spontaneous bursts of activity without external stimuli, helping the synapses to organize properly.

In my layman's view, it's like hallucinating shapes that are important to learn. Very similar to the "priming" described in the article, but easier to visualize (literally).

[1] https://en.wikipedia.org/wiki/Retinal_waves

I feel like the retina, & sight-brain connection more generally, will turn out to be a lot more important to human cognition & consciousness than we realize

AFAIK the whole morphology is decided in distributed computation fashion via electrical potential changes, at least according to experiments by Michael Levin