Early-stage visual processing deficits in schizophrenia

Abstract

Purpose of review: While cognitive dysfunction including memory and attentional deficits are well known in schizophrenia, recent work has also shown basic sensory processing deficits. Deficits are particularly prominent in the visual system and may be related to cognitive deficits and outcome. This article reviews studies of early-stage visual processing in schizophrenia published during the past year. These studies reflect the growing interest and importance of sensory processing deficits in schizophrenia.

Recent findings: The visual system is divided into magnocellular and parvocellular pathways which project to dorsal and ventral visual areas. Recent electrophysiological and behavioral investigations have found preferential magnocellular/dorsal stream dysfunction, with some deficits in parvocellular function as well. These early-stage deficits appear to be related to higher level cognitive, social, and community function. Structural studies of occipital cortex and particularly optic radiations provide anatomical support for early visual processing dysfunction.

Summary: These findings highlight the importance of sensory processing deficits, in addition to higher cognitive dysfunction, for understanding the pathophysiology of schizophrenia. Understanding the nature of sensory processing deficits may provide insight into mechanisms of pathology in schizophrenia, such as N-methyl-D-aspartate dysfunction or impaired signal amplification, and could lead to treatment strategies including sensory processing rehabilitation that may improve outcome.

Figure 1. Partial-windmill and windmill–dartboard conditions

(a) The partial-windmill condition. The pattern elements in the central disk and second annulus contrast reverse to produce a partial windmill. (b, c) Windmill–dartboard condition. The windmill–dartboard stimulus has two distinct phases: windmill, shown in (b), and dartboard, shown in (c). The contrast of the first and third annuli are held constant. Contrast reversal of the pattern elements in the central disk and second annulus result in the change of appearance from a windmill to a dartboard. Reprinted with permission from Elsevier [46].

Figure 2. Partial-windmill and windmill–dartboard conditions

Patients with schizophrenia (Scz) showed significantly reduced second harmonic responses but intact first harmonic responses. This finding of a differential deficit may indicate a significant loss in the magnocellular pathway. Bi, binocular eye condition; DO, dominant eye condition; ND, nondominant eye condition. a, P < 0.01; b, P < 0.05. Reprinted with permission from Elsevier [46].

Figure 3. Fractional anisotropy (FA) image and scatter plot

(a) FA image with circles representing regions of interest based on their placement in the optic radiations on the b = 0 image (not shown). (b) Scatter plot showing relationship between magnocellular-biased steady-state visual evoked potential (ssVEP) responses and FA of optic radiation white matter tracts for patients with schizophrenia. FA measures range from 0 to 1 with 0 representing complete isotropic diffusion (no directional selectivity of water diffusion and hence decreased white matter integrity) and 1 representing complete anisotropy. FA values have been multiplied by 1000. Reprinted with permission from Elsevier [45].