A pioneering study using functional magnetic resonance imaging (fMRI) to look at which regions of the brain are activated when deciding on statements that are true or false. The subjects were given a set of questions that were obviously either true (belief), false (disbelief) or undecidable (uncertainty). Although higher cognitive functions are involved in establishing the truth-value of a proposition, the actual acceptance of that proposition as either true or false is also intimately linked to more primitive areas involved in more emotional responses. A person's beliefs may well be an aesthetic response rather than a rational one.
Functional Neuroimaging of Belief, Disbelief and Uncertainty, by Sam Harris, Sameer A Sheth, and Mark S. Cohen, Annals of Neurology, 2008 [pdf].