Orientation-dependent contextual modulation of contrast in schizophrenia.

INTRODUCTION

Schizophrenia is associated with weakened contextual modulation of visual contrast perception, which is generally predicted by population average neural firing rates in primary visual cortex (V1). We use high field fMRI and a novel task to assess V1-instrinsic and V1-extrinsic mechanisms of atypical contextual modulation in schizophrenia.

METHODS

We examined the BOLD responses of individuals with schizophrenia (SCZ = 34), bipolar disorder (BP = 25), unaffected first-degree relatives of SCZ (SREL = 20), unaffected first-degree relatives of BP (BPREL = 13) and healthy controls (CON = 23). Participants were presented with near- and far-surrounds oriented at 20° and 70° relative to center gratings.

RESULTS

We observed orientation-dependent modulation of V1 BOLD activation to near-surrounds across groups. In particular, the SCZ and CON groups showed significant orientation-dependent contextual modulation (Cohen's dz SCZ = 0.56; CON = 0.63). Surprisingly, the direction of the modulation was opposite of predicted: greater BOLD activation for the condition that was expected to produce suppression.

CONCLUSIONS

Our results differ from previous reports: we observed successful orientation-dependent modulation of V1 activation in SCZ. Furthermore, our results suggest that spatial attention and figure-ground modulation may play an important role in determining the direction and magnitude of orientation-dependent modulation.