| Objective: To investigate the neurul mechanisms underlying emotional processing deficits in patients with major depressive disorder (MDD) by comparing the differences between subjects with and without MDD at the behavioral and brain functional level.Methods: 26 patients with MDD and 20 age and gender-matched normal adults were recruited from the outpatients and inpatients in the Department of Psychiatry, First Hospital of Shanxi Medical University. All the subjects met the following criteria: aged from 18 to 45 years old, right-handed, having no history of major physical illness and suicidal ideas, having no history of psychiatric diseases except for the diagnosis of MDD in the patient group. All of the participants were assessed by the 17-item Hamilton Depressive rating scale (HAMD), with the patients scored not less than 17 points and the controls scored less than 7 points. The subjects were scanned when they were performing an event-related emtional task. The task was presented by the E-prime software, in which three types of pictures (positive, neutral and negative pictures) appeared randomly. And all of the pictures were selected from the International Affective Picture System. The subjects were required to concentrate on the pictures, try to keep the body still, and push the corresponding button to judge the nature of each picture. Behavioral data were analysed using the PASW statistics 18 software, and the average response time and accuracy were calculated and compared between groups. Imaging data were analysed using the DAPRSF, SPM and Xjview software, and one-sample t-tests and independent two-sample t-tests were done.Results: 1. The patient group showed longer reaction time than the control group (791.51±203.20 and 659.77±151.20 ms respectively). The differeces in reaction time were mainly caused by the differeces when observing the negative pictures, with 780.15±196.04 ms in MDD and 645.54±185.79 ms in the controls. No significant overall difference in accuracy were found between groups, but the MDD group showed significantly lower accuarcy when they were exposed to the positive pictures relative to the controls, with 0.84±0.27 and 1.11±0.22 respectively after arcsine square root transformation.2. Compared with the baseline condition, the patient group showed activation in the precuneus and superior frontal gyrus when looking at the positive and neutral pictures and showed activation in the precuneus, superior frontal gyrus and middle frontal gyrus when looking at the negative stimuli. The normal controls showed activation in the cuneus and the middle occipital gyrus when receiving positive picture stimuli, and showed no significant activation when observing the neutral and negative pictures.3. When looking at the positive and neutral pictures, the patient group exhibited more activation in the superior frontal gyrus than the control group. When looking at the negative picture stimuli, the patient group showed more activation in the superior frontal gyrus and middle frontal gyrus than the healthy subjects.4. Correlation analysis showed significant positive correlations between the HAMD score and the reaction time when observing the positive, negative and neutral pictures. That is, the greater the HAMD scores, the longer the reaction time. Significant negative correlations were seen between the HAMD score and the accuarcy of neutral pictures, with the greater the HAMD scores, the lower accuracy when looking at the neutral pictures.Conclusion: Compared with the controls, patients with MDD showed impaired brain function abnormalities, with more regions activated when performing an emotional task (superior frontal gyrus and middle frontal gyrus), slower response (longer mean reaction time), and numbness when looking at the positive pictures. And a negative cognitive bias were observed in MDD, with longer reaction times relative to the controls when exposed to the negative stimuli. |
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