Obsessive-compulsive disorder (OCD) has a long history of speculations concerning its
cause. This article reviews human functional neuroimaging studies of OCD, then presents
data from a study in the nonhuman primate that concerns the localization of brain systems
that may mediate the expression of OCD symptoms. We use these lines of evidence to argue
that increased “neural tone” through a section of the behaviorally disinhibiting “direct” basal
ganglia pathway, relative to tone in the behaviorally inhibiting or moderating “indirect” basal …