In whale brain at least, it appears the larger size is more related to extra
glial cells and other factors:
My pet theory on this is that glial cells are known to stimulate synapse growth and they support synapse function (e.g. by clearing up after firing) - and so the enormous quantity of glial cells in whale brains (9 times as many glial cells in the sperm whale than in the human) - and their huge neurons—both point to an astronomical number of synapses.
My pet theory on this is that glial cells are known to stimulate synapse growth and they support synapse function (e.g. by clearing up after firing) - and so the enormous quantity of glial cells in whale brains (9 times as many glial cells in the sperm whale than in the human) - and their huge neurons—both point to an astronomical number of synapses.
“Glia Cells Help Neurons Build Synapses”
http://www.scientificamerican.com/article.cfm?id=glia-cells-help-neurons-b
Evidence from actual synapse counts in dolphin brains bears on this issue too.