Abstract： Objective:To investigate the efficacy of different frequencies of modified electroconvulsive therapy in patients with depressive disorder and its effect on cognitive function and functional near infrared spectroscopy.Methods:The clinical data from 60 patients with depressive disorder, admitted to The Third People's Hospital of Huzhou between December 2022 and July 2023, were retrospectively analyzed. This study was designed as a case-control study. These patients were divided into three treatment groups according to different treatment methods: Group 1 ( n = 20), Group 2 ( n = 20), and Group 3 ( n = 20). All patients underwent conventional antidepressant therapy. Additionally, Group 1 received six sessions of modified electroconvulsive therapy, Group 2 received eight sessions, and Group 3 received ten sessions. The treatment duration for all groups was 4 weeks. Comparisons were made among the three groups for pre- and post-treatment scores on the 24-item Hamilton Depression Rating Scale, 14-item Hamilton Anxiety Rating Scale, Clinical Global Impression Scale, Mini-Mental State Examination, Wisconsin Card Sorting Test, Trail Making Test Part A (TMT-A), Trail Making Test Part B (TMT-B), and Digit Symbol Substitution Test. Furthermore, the incidence of adverse reactions during treatment was calculated, and the Treatment Emergent Symptom Scale was used to assess the occurrence of adverse drug reactions. Moreover, functional Near-Infrared Spectroscopy was used before and after treatment to evaluate the cognitive function of patients under the Verbal Fluency Task. Results:At 1, 2, and 4 weeks of treatment, the 24-item Hamilton Depression Rating Scale, 14-item Hamilton Anxiety Rating Scale, and Clinical Global Impression Scale scores of Group 2 and Group 3 were significantly lower than those of Group 1 ( Finter-group = 32.09, Ftime = 54.27, Finteraction = 7.53, all P < 0.05; Finter-group = 38.14, Ftime = 69.33, Finteraction = 8.59, all P < 0.05; Finter-group = 11.22, Ftime = 28.29, Finteraction = 9.14, all P < 0.05). The Mini-Mental State Examination, Wisconsin Card Sorting Test, and Digit Symbol Substitution Test scores of Group 1 and Group 2 were significantly higher than those of Group 3, while Trail Making Test Part A and Trail Making Test Part B scores of Group 1 and Group 2 were significantly lower than those of Group 3 ( Finter-group = 14.20, Ftime = 44.27, Finteraction = 6.24, all P < 0.05; Finter-group = 18.23, Ftime = 67.15, Finteraction = 8.54, all P < 0.05; Finter-group = 9.30, Ftime = 75.16, Finteraction = 9.41, all P < 0.05; Finter-group = 19.47, Ftime = 85.76, Finteraction = 9.33, all P < 0.05; Finter-group = 22.26, Ftime = 46.37, Finteraction = 6.52, all P < 0.05). There was no significant difference in the incidence of adverse reactions among the three groups ( Finter-group = 3.03, Ftime = 8.36, Finteraction = 1.25, all P > 0.05). After 4 weeks of treatment, the number of Verbal Fluency Task words and oxy-Hb level in Group 2 were significantly higher compared with those in Group 1 and Group 3 ( F = 29.71, 198.57, both P < 0.05). Conclusion:Modified electroconvulsive therapy is highly effective and safe in treating depressive disorders in patients. Eight sessions of modified electroconvulsive therapy administered within 4 weeks have been shown to exhibit better clinical efficacy and lead to greater improvements in cognitive function and functional near-infrared spectroscopy measurements compared with six or ten sessions of treatment.