Demographics and clinical sample characteristics
34 patients with MDD and 34 healthy individuals were ultimately included in this trial. Among the patients with MDD, the average course of disease was 47.74 months (SD = 29.820), and the mean score on the HDRS-17 was 23.94 (SD = 6.915). Specifically, the mean scores for psychomotor retardation, cognitive impairment, anxiety/somatization, sleep disturbance, and weight factors were 6.65 (SD = 2.538), 4.00 (SD = 2.449), 7.15 (SD = 2.414), 4.88 (SD = 1.038), and 1.47 (SD = 1.440), respectively. 34 patients were treated with antidepressants medications: five with venlafaxine (mean dose 190.0 ± 33.91 mg/day), nine with escitalopram oxalate (mean dose 16.11 ± 4.17 mg/day), six with mirtazapine (mean dose 28.75 ± 9.97 mg/day), four with paroxetine (mean dose 25.0 ± 5.77 mg /day), seven with sertraline (mean dose 167.86 ± 37.40 mg /day), and three with fluoxetine (mean dose 26.67 ± 11.55 mg /day). For patients, the mean Fluoxetine-equivalent dose was 37.43 ± 13.79 mg/d as calculated according to the previous report [30].
Age and years of education data did not follow a normal distribution, the Mann-Whitney U test indicated no statistically significant differences in age and years of education between the two groups (P > 0.05). Gender-ratio met the conditions for a chi-square test, which showed no statistically significant differences between the two groups as well (P > 0.05) (Table 1).
Table 1
Demographic characteristics and clinical information of participants (means and standard deviations)
Variable | MDD (n = 34) | HCs (n = 34) | Test statistic |
Age (years)* | 37.50(27,44) | 34.0(28,36.50) | U = 521.0, P = 0.484 |
Sex (M/F) | 16/18 | 17/17 | χ2 = 0.059, P = 0.808 |
Education (years)* | 13(9,16) | 15(12,15) | U = 458.0, P = 0.133 |
course of disease (month) | 47.74(29.820) | - | - |
HDRS-17 | 23.94(6.915) | - | - |
psychomotor retardation cognitive impairment anxiety/somatization sleep disturbance weight | 6.65(2.538) 4.00(2.449) 7.15(2.414) 4.88(1.038) 1.47(1.440) | - | - |
Medicine (S/E/M/P/V/F) | 7/9/6/4/5/3 | | |
Abbreviations: MDD = major depressive disorder; HCs = healthy controls; Sex (M = Male, F = Female); HDRS-17 = the Hamilton Depression Rating Scale, 17 item; Medicine (S: Sertraline, E: Escitalopram oxalate, M: Mirtazapine, P: Paroxetine, V: Venlafaxine, F: fluoxetine). *Age and years of education data are skewed, represented by the median (P25, P75). |
SePT
RTs for emotional selection task between the MDD group and the HCs group across emotional valence (positive, negative, and neutral) are illustrated in Fig. 2. ANOVA of RTs yielded no significant effect of emotional valence (F2,132 = 0.025, P = 0.975, η2 = 0.000), but revealed a significant of participant group (F1,66 = 5.487, P = 0.022, η2 = 0.077). The interaction between emotional valence and participant group was significant (F2,132 = 4.762, P = 0.010, η2 = 0.067). Simple effect analysis revealed that MDD participants exhibited longer mean RTs for negative stimuli (F1,66 = 5.124, P = 0.027, η2 = 0.072) and positive stimuli (F1,66 = 10.740, P = 0.002, η2 = 0.002) than healthy controls, but there was no significant difference for neutral stimuli (F1,66 = 0.075, P = 0.785, η2 = 0.001). For gender judgment task, the difference in RTs between the two groups was not statistically significant (P > 0.05).
Self-reported preference for emotional selection task between the MDD group and the HCs group across emotional valence (positive, negative, and neutral) are illustrated in Fig. 3. ANOVA of Self-reported preference yielded no significant effect of participant group (F1,66 = 3.116, P = 0.082, η2 = 0.045), but revealed a significant effect of emotional valence (F2,132 = 96.379, P < 0.001, η2 = 0.594). The interaction between emotional valence and participant group was significant (F2,132 = 6.907, P = 0.009, η2 = 0.095). Simple effect analysis revealed that MDD participants showed a higher preference rate for negative stimuli (F1,66 = 5.903, P = 0.018, η2 = 0.082) and a lower preference rate for positive stimuli (F1,66 = 7.884, P = 0. 007, η2 = 0.107) compared to healthy controls. However, the difference in the preference rate for the neutral stimuli was not statistically significant (F1,66 = 0.255, P = 0. 616, η2 = 0.004). Additionally, within-group comparisons revealed that MDD participants exhibited a significantly higher preference for negative stimuli compared to positive and neutral stimuli (P < 0.001).
The average accuracy rate of gender judgment in the MDD group was 90.02% (median = 90.32%); in the HCs group, the average accuracy rate was 91.26% (median = 91.67%). The results suggest no statistical difference in gender judgment accuracy rates between the two groups (Z = -1.048, P = 0.295).
ERP Results
LPP. A 2 (group: MDD, HCs) × 3 (emotion valence: positive, negative, and neutral) × 5 (electrode site: CP1, CP2, CP3, CP4, CPZ) mixed-design ANOVA was conducted for the analysis of LPP.
The results indicated a significant main effect of participant group (F1,66 = 8.381, P = 0.005, η2 = 0.113) and a significant main effect of emotion valence (F2,132 = 6.991, P = 0.010, η2 = 0.096). The interaction between emotional valence and participant group was significant (F2,132 = 3.281, P = 0.012, η2 = 0.047). However, there was no interaction effect between emotion valence, participant group, and electrode site (F8,528 = 0.376, P = 0.856, η2 = 0.006). Simple effect analysis revealed that MDD participants showed higher LPP amplitudes for negative stimuli (F1,66 = 8.656, P = 0.004, η2 = 0.116) and positive stimuli (F1,66 = 2.983, P = 0. 025, η2 = 0.159) compared to healthy controls (Fig. 4).
For LPP latency, there was a significant main effect of participant group (F1,66 = 5.030, P = 0.028, η2 = 0.071) and a significant main effect of emotion valence (F2,132 = 2.624, P = 0.035, η2 = 0.038). The interaction between emotional valence and participant group was significant (F8,528 = 1.940, P = 0.027, η2 = 0.029). No interaction effect was found between emotion valence, participant group, and electrode site (F10,660 = 1.464, P = 0.132, η2 = 0.022). Simple effect analysis revealed that MDD participants showed longer LPP latency for negative stimuli (F1,66 = 3.776, P = 0.039, η2 = 0.056) compared to healthy controls (Fig. 5).
P200. A 2 (group: MDD, HCs) × 3 (emotion valence: positive, negative, and neutral) × 6 (electrode site: F3、FZ、F4、FC3、FCZ、FC4) mixed-design ANOVA was conducted for the analysis of P200. The results indicated a significant main effect of participant group (F1,66 = 6.098, P = 0.016, η2 = 0.085), a significant main effect of emotion valence (F2,132 = 7.976, P < 0.001, η2 = 0.108), and a significant main effect of electrode site (F5,330 = 4.793, P = 0.029, η2 = 0.070). The interaction between emotional valence and participant group was significant (F2,132 = 7.069, P = 0.010, η2 = 0.097). The marginal interaction effect between the participant group and electrode site was observed (F5,330 = 2.222, P = 0.052, η2 = 0.033). There was also a significant main effect between emotion valence, participant group, and electrode site (F10,660 = 4.300, P = 0.042, η2 = 0.061). Simple effect analysis revealed that MDD participants showed higher P200 amplitudes for negative stimuli (F1,66 = 5.065, P = 0.028, η2 = 0.071) and neutral stimuli (F1,66 = 4.828, P = 0. 032, η2 = 0.068) compared to healthy controls (Fig. 6). For negative stimuli, the MDD participants had significantly higher P200 amplitudes compared to the healthy controls at all six electrode sites (P < 0.05). Among them, the largest difference in mean P200 amplitude between the two groups was observed at electrode site F3 (2.155 ± 0.899 µV) (Fig. 6A). For neutral stimuli, the MDD participants had significantly higher P200 amplitudes compared to the healthy controls at three electrode sites (F3, FZ, and F4) (P < 0.05). Among them, the largest difference in mean P200 amplitude between the two groups was observed at electrode site F4 (1.904 ± 0.852 µV) (Fig. 6B). For positive stimuli, no statistically significant difference in P200 amplitudes were found between the two groups across six electrode sites (P > 0.05). However, within-group comparisons revealed that MDD participants exhibited significantly higher P200 amplitudes for negative stimuli and neutral stimuli compared to positive stimuli (P < 0.05) (Fig. 7).
For P200 latency, the results indicated a significant main effect of electrode site (F5,330 = 2.306, P = 0.044, η2 = 0.034). There was no significant main effect of participant group (F1,66 = 2.046, P = 0.157, η2 = 0.030) and no significant main effect of emotion valence (F2,132 = 0.298, P = 0.743, η2 = 0.004). The interaction effect between electrode site and participant group was not significant (F5,330 = 1.968, P = 0.083, η2 = 0.029), and the interaction effect between electrode site and emotion valence was not significant (F10,660 = 1.219, P = 0.275, η2 = 0.018). No interaction effect was found between emotion valence, participant group, and electrode site (F10,660 = 0.683, P = 0.741, η2 = 0.010).
Multiple linear stepwise regression analysis between behavioral data, ERP data, and HDRS-17 scores
In order to find biomarkers for correct diagnosis, appropriate treatment, and predicted outcomes of MDD patients, we specifically investigated the relationships among clinical symptoms, behavioral data, and electrophysiological characteristics in MDD participants.
LPP amplitude. Multiple linear stepwise regression analysis was employed using behavioral data, fluoxetine equivalent dose, total disease duration, and HDRS-17 scores as independent variables and LPP amplitude as the dependent variable. The results found that the negative _ RTs and positive _ RTs entered the regression equation, LPP amplitude was negatively correlated with negative _ RTs (B = -0.008, P = 0.008) and positively associated with positive _ RTs (B = 0.009, P = 0.023) (Table 2). The regression equation is as follows: Y^ = 4.014 − 0.008 * negative _ RTs + 0.009 * positive _ RTs
Table 2
Factors influencing LPP amplitude (n = 34)
| Non Standardized Coefficient | Standardized Coefficient | t | P | VIF | R² | AdjustedR² | F |
B | Standard Error | Beta |
Constant | 4.014 | 6.76 | 0 | 0.594 | 0.557 | - | 0.295 | 0.25 | F = 6.489, P = 0.004*** |
negative_RTs | -0.008 | 0.003 | -0.432 | -2.858 | 0.008*** | 1.005 |
positive_RTs | 0.009 | 0.004 | 0.36 | 2.384 | 0.023** | 1.005 |
Notes: ** P < 0 .05, *** P < 0.01. |
P200 amplitude. Multiple linear stepwise regression analysis was employed using behavioral data, fluoxetine equivalent dose, total disease duration, and HDRS-17 scores as independent variables and P200 amplitude as the dependent variable. The results found that the negative _ RTs and HDRS-17 scores entered the regression equation, P200 amplitude was negatively correlated with negative _ RTs (B = -0.005, P = 0.050) and positively associated with HDRS-17 scores (B = 0.337, P = 0.032) (Table 3). The regression equation is as follows: Y^ = 7.405 − 0.005* negative _ RTs + 0.337* HDRS-17
Table 3
Factors influencing P200 amplitude (n = 34)
| Non Standardized Coefficient | Standardized Coefficient | t | P | VIF | R² | AdjustedR² | F |
B | Standard Error | Beta |
Constant | 7.405 | 3.374 | 0 | 2.195 | 0.036** | - | 0.308 | 0.263 | F = 6.886, P = 0.003*** |
negative_RTs | -0.005 | 0.003 | -0.323 | -2.04 | 0.050** | 1.125 |
HDRS-17 | 0.337 | 0.15 | 0.356 | 2.243 | 0.032** | 1.125 |
Notes: ** P < 0 .05, *** P < 0.01. |
HDRS-17. Multiple linear stepwise regression analysis was employed using behavioral data, fluoxetine equivalent dose, total disease duration, and P200 amplitude as independent variables and HDRS-17 scores as the dependent variable. The results found that the positive_Preference and negative_Preference entered the regression equation, HDRS-17 scores were positively correlated with negative_Preference (B = 6.345, P = 0.009) and negatively associated with positive_Preference (B = − 205.181, P < 0.001) (Table 4). The regression equation is as follows: Y^ = 37.843–205.18* positive_Preference + 6.345* negative_Preference
Table 4
Factors influencing HDRS-17 (n = 34)
| Non Standardized Coefficient | Standardized Coefficient | t | P | VIF | R² | AdjustedR² | F |
B | Standard Error | Beta |
Constant | 37.843 | 1.303 | 0 | 29.053 | 0.000*** | - | 0.89 | 0.883 | F = 125.911 P = 0.000*** |
positive_ Preference | -205.181 | 14.116 | -0.889 | -14.536 | 0.000*** | 1.057 |
negative_ Preference | 6.345 | 2.261 | 0.172 | 2.807 | 0.009*** | 1.057 |
Notes: ** P < 0 .05, *** P < 0.01. |