Rather than between D and R, it should be between conservatives and non-conservatives. Libertarians probably have similar brain patterns when compared to liberals.
http://www.motherjones.com/politics/2013/02/brain-difference-democrats-republicansThe two new studies described here are likely connected: It is hard not to infer that fear of outsiders or those different from you—along with greater fear dispositions in general—may be related to the role of amygdala, a brain structure that has been dubbed the "heart and soul of the fear system." The amygdala has been repeatedly implicated in politics. Indeed, Schreiber's research builds on prior brain studies: In a group of University College of London students, for instance, conservatives showed more gray matter in the right amygdala.