Different extraretinal neuronal mechanisms of smooth pursuit eye movements in schizophrenia: An fMRI study

Smooth pursuit eye movements (SPEM) are necessary to follow slowly moving targets while maintaining foveal fixation. In about 50% of schizophrenic patients SPEM velocity is reduced. In this study we were interested in identifying the cortical mechanisms associated with extraretinal processing of SPEM in schizophrenic patients. During condition A, patients and healthy subjects had to pursue a constantly visible target (10 degrees /s). During condition B the target was blanked out for 1000 ms while subjects were instructed to continue SPEM. Eye movement data were assessed during scanning sessions by a limbus tracker. During condition A, reduced SPEM velocity in patients was associated with reduced activation of the right ventral premotor cortex and increased activation of the left dorsolateral prefrontal cortex, the right thalamus and the Crus II of the left cerebellar hemisphere. During condition B, SPEM velocity was reduced to a similar extent in both groups. While in patients a decrease in activation was observed in the right cerebellar area VIIIA, the activation of the right anterior cingulate, the right superior temporal cortex, and the bilateral frontal eye fields was increased. The results implicate that schizophrenic patients employ different strategies during SPEM both with and without target blanking than healthy subjects. These strategies predominantly involve extraretinal mechanisms.