Event-related electrophysiological data for the target stimulus from the visual oddball task were analyzed. The amplitude envelope of the S-transform time-frequency region was averaged across single trials, per individual, to obtain estimates of event-related total power. Mean power was calculated for each electrode within time-frequency regions of interest that were defined by frequency band ranges and time intervals (Lachaux et al. 2003). The primary phenotype used for the family GWAS was the total power in the theta (3.0-7.0 Hz) oscillation at the frontal midline channel (Fz) extracted from the 300-700 ms time window, which corresponds to the window of the P300 component in the event-related waveforms. The total theta power measure was also extracted for the central (Cz) and parietal (Pz) channels for secondary analyses. As the theta ERO phenotype showed significant age and gender effects with amplitude, age and gender were included as covariates in the genetic analyses.
