Between-group differences in neuropsychological measurements
Table 1 presents the comparison of the demographic and neuropsychological measurements between groups. The mean full-scale intelligence quotient of the ADHD-L group was lower than that of the TD group (p = 0.013); however, the verbal comprehensive index did not differ among the groups, which confirmed that all the participants completely comprehended the test instructions. CPI differed significantly between groups; specifically, the ADHD-L group performed worse than the TD and ADHD-H groups (p < 0.001 for both).
Significant between-group differences were observed in the DBDRS and K-CPT2 scores. Regarding the DBDRS, the participants in the two ADHD groups were rated higher scores than those in the TD group on the inattentive dimension by both parents (13.11 ± 4.35 in ADHD-H, 14.69 ± 5.10 in ADHD-L, 10.75 ± 4.61 in TD, p = 0.047) and teachers (15.28 ± 5.00 in ADHD-H, 17.13 ± 4.16 in ADHD-L, 9.10 ± 5.97 in TD, p < 0.001). On the hyperactive dimension, teachers gave the participants with ADHD higher scores than those in the TD group (13.39 ± 5.78 in ADHD-H, 14.19 ± 6.03 in ADHD-L, 8.25 ± 7.74 in TD, p = 0.017). Regarding the K-CPT2, the ADHD-L group exhibited inferior HRT performance (i.e., had higher HRT scores) to other groups (53.28 ± 5.94 in ADHD-H, 63.75 ± 7.51 in ADHD-L, 55.05 ± 5.84 in TD, p < 0.001). The ADHD-L group performed worse (i.e., scored higher) than the TD group in detectability (54.38 ± 8.30 in ADHD-L, 48.10 ± 6.21 in TD, p = 0.035), omission (55.06 ± 9.59 in ADHD-L, 47.90 ± 9.34 in TD, p = 0.047), HRT SD (55.56 ± 10.79 in ADHD-L, 46.95 ± 6.72 in TD, p = 0.007), and HRT ISI changes (56.38 ± 11.33 in ADHD-L, 49.00 ± 7.12 in TD, p = 0.031). Although the ADHD-H group exhibited a poorer performance than the TD group did, the K-CPT2 scores of these groups did not differ significantly (Table 1).
Between-group differences in resting relative spectral power and power ratios
Data on the relative powers of delta, theta, alpha, beta, and the TBR on eight electrodes (Fp1, Fp2, Fz, C3, C4, Pz, O1, and O2) at rest indicated no significant differences between the groups (Supplemental Table 1).
Between-group differences in CPT-task-related relative spectral power and power ratios
Between-group differences in CPT-slow-rate task-related relative spectral power and power ratios
The relative powers of delta, theta, alpha, beta, and the TBR on eight electrodes (Fp1, Fp2, Fz, C3, C4, Pz, O1, and O2) in the slow-rate task condition among the three groups were compared (Supplemental Table 2). Table 2 and Fig. 5 present the significant results from the analysis of between-group differences in the slow-rate task-related PSD. The ADHD-H group had a trend of higher delta values than the TD group did on the C4 electrode (p = 0.023), and the ADHD-L group had significantly higher delta values than the TD group did on the Pz electrode (p = 0.007). The ADHD-L group had a trend of lower alpha power values than the TD group did on the Pz electrode (p = 0.040). The beta power values on the Pz electrode tended to be lower in the ADHD-L group than in the TD group (p = 0.025). Overall, trends of between-group differences were observed in the TBR (p = 0.030).
Between-group differences in CPT-fast-rate task-related relative spectral power and power ratios
Table 2 and Fig. 5 present the significant results from the analysis of between-group differences in the task-related PSD. The relative powers of delta, theta, alpha, beta, and the TBR on eight electrodes (Fp1, Fp2, Fz, C3, C4, Pz, O1, and O2) in the fast-rate task condition among the three groups were compared (Supplemental Table 3). The delta power values were significantly higher in the ADHD-L group than in the ADHD-H group (p = 0.003), and presented a trend to have higher values than did the TD group on Pz electrode (p=0.033). A trend which the ADHD-L group had higher values than did the TD group (p=0.021) and the ADHD-H group (p=0.023) on O1 electrodes was observed. Regarding the alpha power, the ADHD-L group had a trend of lower values than did the ADHD-H group on Pz electrode (p=0.048). Moreover, the beta power values on the Pz electrode were significantly lower in the ADHD-L group than in the ADHD-H group (p = 0.003). Significant differences between ADHD-L and ADHD-H were observed on Pz TBR (p=0.003); a trend of difference between ADHD-L and ADHD-H were observed on C3 TBR (p=0.028).
EEG spectral power alterations of groups under three conditions
Relative delta
Significant main effects were noted for region (F = 2.922, p = 0.006). Specifically, a significant difference was noted between the Pz and O1 electrodes (p = 0.001). No other significant main effects or interactions were observed.
Relative theta
Significant main effects were noted for region (F = 3.019, p = 0.004). Specifically, a significant difference was noted between the Fp2 and Pz electrodes (p = 0.042). Moreover, a significant interaction effect was observed between condition and region (p = 0.001).
Relative alpha
Significant main effects were observed for condition (F = 19.791, p < 0.001). The post hoc test revealed significant shifts from rest to the slow-rate task and from rest to a fast-rate task (p < 0.001 for both). Main effects were also observed for region (F = 3.222, p = 0.003), and the post hoc test revealed significant differences between the Pz and O1 electrodes (p = 0.024) and between the Pz and O2 electrodes (p = 0.046). Significant interaction effects of condition and region were also noted (p = 0.012). Notably, condition and group had a significant interaction effect (p = 0.040), and the post hoc test indicated that the ADHD-L group experienced a decline in alpha power during the shift from rest to the slow-rate task (p = 0.003) and from rest to a fast-rate task (p < 0.001). A reduction in alpha power was observed in the ADHD-H group during the transition from rest to the slow-rate task (p < 0.001). The aforementioned results were distinct from those obtained for the TD group, which exhibited no obvious differences in transition patterns. Figure 6 presents the transition patterns of the three groups in the three conditions.
Relative beta
Significant main effects were observed for region (F = 2.040, p = 0.049), and a significant difference was noted between the Pz and O1 electrodes (p = 0.006). No other significant main effects or interactions were observed.
Between-group differences in task-based coherence and their correlations with behavioral rating scores
We compared the task-related coherence of all 28 electrode pairs in the four frequency bands among the three groups (Fig. 7). Table 3 lists the significant results from the analysis. Regarding beta coherence, the ADHD-H group had significantly lower values than the TD group on the Fp2–O2 electrode pair (p = 0.028). On the C3–C4 electrode pair, the ADHD-L group had significantly lower beta coherence values than TD group (p = 0.022). The correlation analysis indicated significant negative correlations between the beta coherence on the C3–C4 electrode pair and all DBDRS scores except the inattentiveness dimension score rated by the parents (Table 4).