Rationale: Suppression of middle latency auditory evoked responses is considered an index for the multistage sensory gating process. This has been observed in sequentially occurring P50, N100 and P200 components in a dual-click procedure. Since P50 sensory gating deficits have been observed in schizophrenic patients and first degree relatives, this parameter was suggested as an intermediate phenotype of the disease. However, most studies only show a low reliability for P50 sensory gating and neither N100 nor P200 sensory gating have been sufficiently tested.
Methods: Reliability of P50, N100 and P200 sensory gating was measured in 41 healthy subjects in two sessions, four weeks apart, using intra-class correlation. Sensory gating was calculated as ratio-gating (second response magnitude/first response magnitude x100) as well as difference-gating (first response magnitude minus second response magnitude).
Results: The difference-gating showed good to excellent reliabilities independently of the amplitude-measurement method applied (P50 peak-to-peak 0.75 and baseline-to-peak 0.74, N100 peak-to-peak 0.63 and baseline-to-peak 0.70, P200 peak-to-peak 0.82 and baseline-to-peak 0.79). Regarding ratio-gating, best temporal stability was observed for the P200 (peak-to-peak 0.58 and baseline-to-peak 0.62). Reliability of P50 ratio-gating strongly depends on the amplitude-measurement method (peak-to-peak 0.0 and baseline-to-peak 0.46).
Conclusion: Regarding long-term reliability in healthy subjects the difference-gating of all three evoked responses and the ratio-gating of the P200 component may be useful tools for clinical or intermediate phenotype studies measuring different stages of the auditory sensory gating process. In contrast, the reliability of the P50 and N100 ratio-gating component seems to be insufficient for this purpose. However, long-term reliability remains to be confirmed in clinical samples.