Electrophysiological correlates of visual backward masking in first-episode psychosis

Schizophrenia is a heterogeneous disorder and among other symptoms, patients have important visual impairments. Visual paradigms are therefore important tools to investigate the mechanisms of schizophrenia. We have previously shown that visual backward masking (VBM) is a very sensitive endophenotype of schizophrenia (Chkonia et al., 2010). Moreover, we found strongly reduced global field power (GFP) amplitudes for masked stimuli in schizophrenia patients (Plomp et al., 2013). In order to track the progress of the disease and its behavioral and electrophysiological correlates, we tested 11 patients with first-episode psychosis three times during one year in a longitudinal study. A vernier target (i.e. two vertical bars that are slightly offset in the horizontal direction), was presented and after the target, a mask followed. Task was to discriminate the offset direction by pushing a corresponding button. Two masking conditions (long and short inter-stimulus intervals (ISI)) were randomly presented along with target only and mask only conditions; in parallel the EEG was recorded. First-episode patients showed clear masking deficits and reduced amplitudes in the EEG compared to controls, but higher amplitudes compared to chronic schizophrenia patients. The amplitudes remained stable across the first year. Hence, masking deficits are present already at the very beginning of the disease. We suggest that visual backward masking is a very sensitive endophenotype of the schizophrenia spectrum.