The comment on size is interesting - my understanding was speed of transmission was limited by size (as well as by myelination or lack of myelination) but didn't know noise was another issue that related to size:
"our neurons could be much smaller than they actually are. If you packed all material necessary for sending signals as tightly as possible, the branches of a neuron (called axons) would measure just .06 microns [about 2.3 millionths of an inch] across. In fact, the thinnest axons are about .1 microns [about 4 millionths of an inch]. Recent studies have shown that it's noise that prevents them from getting thinner. The thinner an axon gets, the noisier it becomes. Below .1 microns, the noise abruptly rises so much that it drowns out any signal. We might be far smarter if noise didn't keep us from growing more neurons."
Zimmer makes it sound like noise is a problem the brain must overcome. Buzsáki figures it's there for a reason, calls it "deep brain activity", even suggests it is necessary for cognition.