isabella, i don't think the original question was just about the neurobiology of deception, but of inaccurate perception and delusion. they certainly can relate to each quite a lot, but i think we may come up with slightly different answers based on the distinction.

delusion is discernible quite frequently neurobiologically. consider how often delusional perceptions bring someone to the attention of a psychiatrist or neurologist. hearing voices or believing a ghost is following you or something like that is usually something we can and do get an idea about what's going wrong in the brain, especially if it's the result of a lesion. check out their sensory circuits for problems. too much dopamine as cause can be tested with a dopamine-reducing drug, though i wish there were more direct ways...

now if we're talking about popular and somewhat adaptive delusions in an otherwise functioning person...

i suppose you could witness the signalling going on and deduce certain things. beliefs occur more quickly than disbelief or uncertainty in the brain; you could look for amygdala metabolism and see if it's playing a part in an fMRI while the person stated the beliefs in question, and whether it's most active along the thalamus-amygdama or thalamus-cortex pathway to see how much more automated emotional resonses are active... you could measure galvanic skin response for signs of unconscious conflict.

the thing with deception vs. delusion is that delusion may not have signs of inner inconsistency the way deception would. people may believe a delusion all the way, through and through, i would suppose. it depends on the nature of the belief or perception.