Compensation of visual backward masking deficits in relatives of schizophrenia patients

Visual backward masking (VBM) is a potential endophenotype of schizophrenia reflecting the genetic underpinnings of the disease (Chkonia et al., 2010). Masking deficits are highly correlated with reduced N1 amplitudes as shown by the Global Field Power (GFP; Plomp et al., 2013). Here, we investigated the electrophysiological correlates of VBM in non-affected first-order relatives of schizophrenia patients. We tested a large sample of schizophrenia patients, first-degree relatives and matched healthy controls, in a VBM paradigm while recording the electroencephalography (EEG). In our VBM paradigm, a vernier target, i.e. two vertical bars that are slightly offset in the horizontal direction, followed by a mask. The participants had to discriminate the offset direction by pushing the corresponding button. We had three conditions: target only and two VBM conditions, with long and short inter-stimulus intervals (ISI). Patients’ performance was impaired, while the relatives performed at the same level as the controls. Performance was significantly correlated with the EEG N1 amplitude, as measured by the GFP. Most interestingly, N1 amplitudes were higher in relatives compared to controls for target only and short ISI, while they were lower in patients relative to controls as previously reported (Plomp et al., 2013). For the relatives, N1 amplitudes were at the same level in all conditions; however, for controls and patients, N1 amplitudes increased with task difficult, e.g., amplitudes in the long ISI condition were lower than in short ISI condition. Our results suggest that relatives use a compensation mechanism tuning the brain to maximum performance in VBM. However, as relatives are already at the peak of their activations, increasing task difficulty does not change brain processing.