There is still circuitry that we don't fully understand, along with the role of glia in information processing and with mysteries surrounding the processing capabilities of synapses/receptors and neuronal oscillations. That's not even the half of it.

There is so much in the way of biochemical pathways such as regulation of neurotransmitters and receptor and other protein trafficking and modification that the complexity is insanely difficult to comprehend.

And I haven't even mentioned the neuroendocrine system.