Scatterplots of S1 and S2 amplitudes, and suppression ratios averaged across all 4 sites for P50 waves are presented in and . A significant main effect of group on P50 suppression was observed (F3,82 = 2.94, P = .04). SZ patients had a significantly higher P50 S2:S1 ratio (mean = 0.76, SD = 0.35) than HCs (mean = 0.56, SD = 0.31; P < .001). P50 ratio showed a trend to be higher in relatives (mean = 0.68, SD = 0.46) than in HCs (P = .09). Patients (mean = 2.22, SD = 1.11; P = .57) and relatives (mean = 2.47, SD = 1.46; P = .58) did not differ from HCs (mean = 2.41, SD = 1.48) in amplitude of the S1 wave. However, patients (mean = 1.58, SD = 0.91) and relatives (mean = 1.55, SD = 1.06) had larger S2 amplitudes than HCs (mean = 1.37, SD = 1.18) but only patients differed significantly from controls (P < .01). In the patient group, illness-related factors, smoking status, and number of daily cigarettes were not significantly associated with P50 ratio, S1 amplitude, or S2 amplitude (all P values >.05).
Fig. 1. Scatterplot Distribution of P50 Event–Related Potential Variables by Group (Top: P50 Ratio; Bottom: S1 [Left] and S2 [Right] Amplitudes [μV]). S1 amplitude, S2 amplitude, and S2:S1 ratio for each subject are the average values based on (more ...)
Fig. 2. Examples of Grand Average P50 Responses for Each Group (Top: Healthy Control [HC; Ratio 0.66]; Middle: Schizophrenia Patient [Ratio 0.85]; Bottom: Relative [Ratio 0.80]). The thick line shows the response to the S1 click and the dotted line shows the (more ...)
shows group means and SDs of gamma- and beta-evoked power to S1 and S2 stimuli at each ROI. Widely distributed reduced gamma power to S1 stimuli (in 10 out of 13 ROIs) was found in patients compared with HCs (P < .001 in all, ). Gamma power to S2 stimuli was significantly reduced at Pz (P = .001), left temporal (P = .002), and left parietal (P < .001) ROIs (). HCs and relatives did not differ significantly in gamma power at any ROI ( and ).
Group Means and SDs of Gamma and Beta Power to S1 and S2 Stimuli at Each Region of Interest
Fig. 3. Gamma and Beta Event–Related Oscillation (ERO) Activity to S1 Stimuli in Healthy Controls (HCs, Left), Schizophrenia (SZ) Patients (Center), and Unaffected Relatives of SZ Patients (Right). Electroencephalogram frequency is indicated on the y-axis. (more ...)
Fig. 4. Gamma and Beta Event–Related Oscillation (ERO) Activity to S2 Stimuli in Healthy Controls (HCs, Left), Schizophrenia (SZ) Patients (Center), and Unaffected Relatives of SZ Patients (Right). Electroencephalogram frequency is indicated on the y-axis. (more ...)
Means and SDs of gamma gating (S2-S1 difference) at each ROI for each group are shown in . Compared with HCs, patients showed gamma-band gating deficits at Fz, left temporal, Pz, left parietal, left occipital, and right occipital ROIs. HCs and relatives did not differ significantly in gamma gating at any ROI.
Raw Scores and Group Comparison of Gamma and Beta Gating
Partial correlation coefficients revealed that age of onset was significantly associated with gamma EROs. For the S1 response, age of onset was significantly associated with gamma power at the Fz (r = .48, P = .001), Pz (r = .32, P = .04), bilateral frontal (LF: r = .48, P = .001; and RF: r = .45, P = .003), and bilateral central-parietal (LCP: r = .51, P = .001; and RCP: r = .51, P = .001) sites. For the S2 response, age of onset was significantly associated with gamma power at the Fz (r = .43, P = .005), Cz (r = .49, P = .001), and bilateral frontal (LF: r = .47, P = .002; and RF: r = .37, P = .02) sites; the younger the age of onset, the smaller the gamma ERO response. Medication dose in CPZ equivalents was modestly but significantly negatively associated with gamma gating at the left (r = −.31, P = .05) and right occipital (r = −.33, P = .04) ROIs; the higher the dose, the less the gating deficit.
Compared with HCs, patients showed significantly reduced beta power activity to S1 stimuli at the Pz, right temporal, and left parietal sites (P < .001 in all, ). Widely distributed reduced beta power to S2 stimuli (in 8 out of 13 ROIs) was found in the patient group (P < .001 in all, ). In the relatives, beta power to S1 and S2 stimuli was not reduced at any ROI ( and ).
Means and SDs of beta gating for each group at each ROI are shown in . Compared with HCs, patients showed deficits in 8 of 13 ROIs, with differences most pronounced at temporal and posterior areas, including: Pz, left temporal, bilateral central parietal, bilateral parietal, and bilateral occipital (). HCs and relatives did not differ significantly at any ROI.
Age of onset was significantly associated with beta EROs; the younger the age of onset, the smaller the beta ERO response. For the S1 response, age of onset was significantly associated with beta ERO at the right frontal (r = .35, P = .03), Pz (r = .58, P < .001), bilateral central-parietal (LCP: r = .37, P = .02; and RCP: r = .37, P = .02), bilateral parietal (LP: r = .56, P < .001; and RP: r = .58, P < .001), and bilateral occipital (LO: r = .42, P = .005; and RO: r = .40, P = .008) sites. For the S2 response, age of onset was significantly associated with beta ERO at Cz (r = .40, P = .009). Beta gating was significantly associated with age of onset in 10 of 13 ROIs (r = .32–.57, all P values <.05) except left temporal, left occipital, and left frontal ROIs, indicating that the younger the age of onset, the greater gating deficit. Medication effects were not significantly associated with beta EROs.
Correlations Among Gating, Amplitude, and Power Measures
shows the correlations of P50 ERPs with gamma and beta responses for each group at Cz. P50 gating was not significantly correlated with either gamma or beta gating at Cz in all 3 groups. No significant association between the P50 ratio and either gamma or beta responses to S1 or S2 stimuli was found either. Gamma and beta gating were not significantly correlated with each other in HCs or relatives but were positively correlated in patients (r = .47, P = .04). In HCs, P50 S1 amplitude was not significantly associated with beta or gamma responses but was significant with beta response to S1 (r = .81, P < .001) in relatives and S2 (r = .46, P = .04) in patients. P50 S2 amplitude was significantly associated with beta power in response to both S1 and S2 stimuli (S1 r = .60; S2 r = .61), and with gamma power in response to S1 stimuli (r = .71) in HCs. Patients did not show such associations (r = .09–.29).
Correlations of P50 ERPs with Gamma and Beta Responses in Each Group at Cz