Vision system indicators of anomalous functional brain organization among patients with schizophrenia: Selective dorsal pathway impairment

Research investigating the etiology of schizophrenia (SCZ) has largely failed to integrate its findings within models of normal brain development or evolution. The current research utilizes an evolutionary model of brain development, the Dual Trends Theory (DTT), to understand the cognitive and neurobiological abnormalities in SCZ. The DTT argues that neural architecture develops along two separate pathways: the dorsal 'archicortical' trend and the ventral 'paleocortical' trend. The DTT dovetails with the leading paradigm of primate vision that also distinguishes two independent pathways in the brain: one devoted to processing spatial, motion and visuomotor aspects of our visual world (i.e., dorsal trend), the other for processing features necessary for object perception and identification (i.e., ventral trend). The current series of studies tested the hypothesis that SCZ is associated with disproportionate dysfunction in dorsal brain circuitry by utilizing visual tasks known to dissociate these pathways. In Study l, dorsal and ventral visual perceptual and visual working memory tasks were administered to patients with SCZ and controls. The results indicated selective SCZ impairment in dorsally mediated visual perception and intact ventrally mediated visual perception. Moreover, a similar, albeit weaker, dissociation was evidenced for perceptual working memory. In Study 2, the relative integrity of these pathways was examined using a size-contrast visual illusion paradigm. In this paradigm, controls typically modulate their perceptual judgments of object size as a function of illusion conditions while their goal-directed actions remain yoked to veridical object properties. However, SCZ patients demonstrated illusion effects for both perceptual judgments and goal-directed actions, consistent with spared ventral and dysfunctional dorsal stream circuitry, respectively. Collectively these studies suggest that neurodevelopmental abnormalities in SCZ may disproportionately affect dorsal brain systems.