Electrophysiological correlates of visual backward masking in patients with first episode psychosis

Abstract

Visual backward masking is strongly impaired in patients with schizophrenia. Masking deficits have been proposed as potential endophenotypes of schizophrenia. Masking performance deficits manifest as strongly reduced amplitudes in the electroencephalogram (EEG). In order to fulfill the criteria of an endophenotype, masking deficits should not vary substantially across time and should be present at the first psychotic event. To verify whether these conditions are met for visual backward masking, we tested patients with first episode psychosis (n=21) in a longitudinal study. Patients were tested with visual backward masking and EEG three times every six months over a period of one year. We found that the EEG amplitudes of patients with first episode psychosis were higher as compared to those of patients with schizophrenia but lower as compared to those of unaffected controls. More interestingly, we found that the EEG amplitudes of patients with first episode psychosis remained stable over the course of one year. Since chronic schizophrenia patients have strongly reduced amplitudes, we speculate that the neural correlates of masking deficits (EEG amplitudes) continue to decrease as the disease progresses.

Electrophysiological correlates of visual backward masking in patients with bipolar disorder

“…In SZ and in patients with first-episode psychosis, masking deficits are associated with decreased neural amplitudes of the N1 component at around 200 ms, as determined by the global field power (GFP) (28,32). Similar results were found in healthy students scoring high in schizotypal traits (30).…”

“…As in previous work (31,32,(38)(39)(40), the following four conditions were tested ( Figure 2A): (1) Vernier Only, i.e., the vernier was presented alone for 30 ms; (2) Long SOA, i.e., the vernier was followed by the mask with an SOA of 150 ms; (3) Short SOA, i.e., the vernier was followed immediately by the mask with an SOA of 30 ms; and (4) Mask Only, i.e., the mask was presented for 300 ms (control condition). For each observer, eight blocks of 80 trials (20 trials/condition in pseudo-random order) were presented.…”

“…Each participant performed twice; for each type of mask, the two runs were averaged and then submitted to statistical analysis. Participants with mean SOAs longer than 300 ms for the 25-elements mask and longer than 450 ms for the 5-elements mask, i.e., twice the mean SOAs of SZ in previous works (23,25,38), were excluded at this stage (2 SZ and 2 BP).…”

“…VD was fixed to 30 ms, i.e., the average VD for SZ according to previous studies (23,25). Two SOA durations corresponding to the mean performance level of controls (30 ms) and of SZ (150 ms) were used (23,25,38).…”

“…Evidence for an endophenotype for schizophrenia comes from a series of studies showing that, first, SZ and schizoaffective patients have strong and reproducible performance deficits (25,26). Second, masking deficits are already present in adolescents with psychosis (27) and with first-episode psychosis (28). Third, masking deficits are state-independent (23).…”