Visual masking in Schizophrenia: an endophenotype and its neural correlates

Objective: In visual backward masking, a target is followed by a mask, which deteriorates performance on the target. Masking is a very sensitive endophenotype for schizophrenia. Patients and their siblings (to a lesser extent) show strong performance deficits. Here, we investigate EEG correlates of masking across the schizophrenia continuum. Method: We measured high-density EEG, while performing a masking task. We report the Global Field Power (GFP), which is the standard deviation across all electrodes. Results: First, schizophrenia patients (n=90) have strongly reduced GFP amplitudes as compared to controls (n=76). The reduced amplitudes imply an attention allocation deficit in schizophrenia associated with the cholinergic system. Second, patients with first episodes psychosis (n=21) have reduced GFP amplitudes when compared to controls (n=20), but higher amplitudes when compared to schizophrenia patients (n=22). The neural correlates are in an intermediate state, implying a progressive development of the disease through time. In addition, the amplitudes remain stable for at least one year (n=11), suggesting that further deficits emerge slowly over time. Third, healthy participants with high schizotypal traits (n=25) have reduced GFP amplitudes compared to low schizotypal participants (n=20). These deficits are similar to the ones of patients, though strongly attenuated, showing that the mechanism is independent of the state of an individual (i.e., health or disease). Fourth, healthy relatives of schizophrenia patients (n=55) have higher GFP amplitudes compared to controls. We propose that the relatives use a compensation mechanism to counterbalance for their masking deficits. Finally, patients with the 22q11.2 deletion syndrome (n=19), who have a 30% risk for schizophrenia, have slightly higher GFP amplitudes when compared to controls (n=18). Conclusion: Observers with psychosis related traits or symptoms have difficulties to enhance faint visual information 200 ms after onset which explains their lower performance in visual backward masking.