This recent post on the nature of the prefrontal cortex from Neuroskeptic is worth a read. It reviews a current article which argues that the prefrontal cortex operates in a holistic manner (e.g. all together) rather than as distinct, independently functioning parts. I'm simplifying things a bit here, so check out the post and the original article for a more thorough version.
The post also includes a snippet reference to phrenology, so, bonus.
This is a great reminder of the complexity of the cortex in general and the importance of those "association areas" your textbook describes.