Factor one, familiarity and frontal cortex: a challenge to the two-factor theory of delusions.

INTRODUCTION: Two-factor theory suggests delusions require two neuropsychological impairments, one in perception (which furnishes content), and a second in belief evaluation (that augers formation and maintenance). Capgras delusion; the belief that one's loved one has been replaced by an imposter, then entails two independent processes; first a lack of skin conductance response to familiar faces so the loved one feels different. This has been demonstrated in four patients with damage to the ventromedial prefrontal cortex (vmPFC) but who do not have delusions. Thus two-factor theorists demand a second factor: a change in belief evaluation, which is associated with damage to the right dorsolateral prefrontal cortex (rDLPFC).
METHODS: Literature review of foundational and related papers on the cognitive neuropsychology of delusions, perception and belief.
RESULTS: The four vmPFC patients appear together in another publication, uncited by two-factor theorists, in which the full extent of their damage is documented. These four cases not only lack skin responses to familiar faces, but lack responses to salient psychological stimuli more generally, which challenges factor one. They also have damage outside vmPFC, including damage to rDLPFC, which challenges factor two.
CONCLUSION: Two-factor theory is found lacking and should be reappraised.