I would like to know if there has been a comparison of the differences between dogs, wolves, monkeys, or any mammals in the specific brain areas, primarily the pre-frontal cortex.
I agree with Lucile, check out the papers of Suzana Herculano-Houzel. She is a real expert in this field and has some very interesting ideas and articles.
Robert Barton has published several comparative works that looked at specific (usually sensory) brain structures:
1 Barton R, Purvis A, Harvey PH. 1995. Evolutionary radiation of visual and olfactory brain systems in primates, bats and insectivores. Philos Trans R Soc Lond B Biol Sci 348:381–392.
2 Barton R. 2006. Olfactory evolution and behavioral ecology in primates. Am J Primatol 68:545–558.
3 Barton R, Harvey PH. 2000. Mosaic evolution of brain structure in mammals. Nature 405:1055–1058.