The role of the right hemisphere in the Capgras delusion.

Following a general review of the literature linking right hemisphere dysfunction to psychoses in general and Capgras delusion (CD) in particular, two studies are described that confirm the link. Study 1 revealed that, compared with matched psychiatric controls, 3 CD patients were particularly poor at matching pairs of faces shown briefly in the left visual field-which implies dysfunctioning right hemisphere performance. However there was no difference in performance when the faces appeared bilaterally, which fails to support the hypothesis that poor interhemispheric communication may give rise to CD. The second study involved tests of face memory and word memory. CD and other delusional misidentification groups scored markedly low on the face test, again implying right hemisphere deficit. Finally, a model of what may be the right hemisphere mechanisms giving rise to CD was explored. This assumes two routes to face recognition, ventral and dorsal. It is argued that exclusive damage to the former may cause prosopagnosia and problems in the latter may give rise to the symptoms of CD.