In this randomized double-blind, placebo-controlled study 72 healthy participants performed smooth pursuit eye movements (SPEM), prosaccades and antisaccades while being randomly assigned to one of four drug groups (intravenous 100 ng/ml ketamine, 2mg oral risperidone, 100 ng/ml ketamine plus 2mg oral risperidone, placebo).
Drug administration did not lead to harmful adverse events. Ketamine increased saccadic frequency and decreased velocity gain of SPEM (all p<0.01) but had no significant effects on prosaccades or antisaccades (all p≥0.07). An effect of risperidone was observed for amplitude gain and peak velocity of prosaccades and antisaccades, indicating hypometric gain and slower velocities compared to placebo (both p≤0.04). No ketamine by risperidone interactions were found (all p≥0.26).
The results confirm that the administration of ketamine produces oculomotor performance deficits similar in part to those seen in schizophrenia. The atypical antipsychotic risperidone did not reverse ketamine induced deteriorations. These findings do not support the cognitive enhancing potential of risperidone on oculomotor biomarkers in this model system of schizophrenia and point towards the importance of developing alternative performance-enhancing compounds to optimize pharmacological treatment of schizophrenia.