Localization of Early-Stage Visual Processing Deficits at Schizophrenia Spectrum Illness Onset Using Magnetoencephalography

Abstract

Impairments in early-stage visual processing are observed in chronic psychosis. However, their presence, localization within the brain, and contribution to cognitive symptoms remain less well established early in disease course. The present study utilized magnetoencephalography (MEG) to examine sensory responses within primary visual cortex (V1). MEG was recorded from 38 individuals diagnosed with a schizophrenia spectrum illness at first psychotic episode (FESz) and 38 matched healthy controls (HC) during visual search tasks. The inverse solution for cortical activity contributing to the M100 visual evoked field was derived. Task performance and V1 activation were compared between groups. FESz exhibited a reduced V1 response relative to HC. This group deficit, however, was selective for the left hemisphere (LH). A similar interaction was observed for response time with FESz exhibiting slower responses to right visual field targets, a difference not observed among HC. Among FESz, larger LH V1 activity was associated with larger hallucination subscale scores on the Scale for the Assessment of Positive Symptoms. Early-stage visual processing deficits localized to V1 are present at disease onset in the schizophrenia spectrum. This impairment appears to be restricted to the LH, consistent with previous reports detailing a predominantly LH disease process in early psychosis, and activity within this region was associated with an increased experience of hallucinations. These findings detail the cortical responses contributing to visual processing impairments and their relationship with symptoms at disease onset, advancing our understanding of their developmental trajectory over the course of psychotic illness.

Keywords: first-break; lateralization; schizophrenia spectrum; sensory impairment.

Fig. 1.

Pop-out and serial search tasks. Participants were instructed to identify the target annulus based on the color cue and then indicate via button-press the side on which the gap appears on the target.

Fig. 2.

Butterfly plots of visual evoked field (VEFs) in response to stimulus array collapsed across tasks. The gray box indicates the 75- to 100-ms time window of interest. Plots depict data recorded from one set of gradiometers.

Fig. 3.

Cortical activity averaged over 75- to 125-ms post-stimulus array collapsed across tasks for HC (A) and first psychotic episode (FESz) (B). Bar graph depicts activity averaged across the V1 ROI. Of note, the scale has been set differently for healthy controls (HC) and FESz to allow for proper visualization of cortical activity. Error bars represent SEM.