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This page is an AI-assisted Turkish summary of the study presented at the 26th World Congress of Psychiatry. The study belongs to the presenting authors; please refer to the original source when citing it.

SO154

Motor-dominant dynamic brain-state phenotype in major depressive disorder and its clinical significance

A MOTOR-DOMINANT DYNAMIC BRAIN STATE PHENOTYPE IN MAJOR DEPRESSIVE DISORDER AND ITS CLINICAL RELEVANCE

Major depressive disorder is associated with an increased tendency to transition into and remain in a motor-dominant brain state at rest, and this dynamic feature has been linked to symptom severity.

The study aimed to identify clinically meaningful aberrant dynamic brain-state phenotypes in major depressive disorder (MDD) using resting-state functional magnetic resonance imaging (fMRI) data and to determine whether the organization of state transitions is altered beyond static connectivity abnormalities. The sample comprised 171 patients with MDD and 131 healthy controls; the groups were similar in age (25.05 ± 6.03 versus 24.02 ± 3.40; p=0.078) and sex (female/male 132/39 versus 89/42; p=0.095), but differed in years of education (16.10 ± 1.51 versus 15.43 ± 1.91; p=0.001). Regional time series were extracted using the BN 246 atlas, and whole-brain dynamic states were identified using a hidden Markov model (HMM); the number of states was determined based on activation map similarity and the Bayesian information criterion, and group comparisons were performed using ANCOVA with false discovery rate (FDR) correction. Six recurring whole-brain states were identified; among them, State 4, centered on the somatomotor network and dominated by the supplementary motor area (SMA), premotor cortex, and primary motor cortex, showed the most consistent abnormality. Fractional occupancy, mean lifetime, and occurrence frequency of State 4 were significantly higher in the MDD group (q_FDR < 0.05), and transition analysis revealed an increased tendency to enter this state. Within the MDD group, engagement in State 4 was positively associated with HAMD scores (partial rho = 0.31; q_FDR = 0.0013), and individual-level prediction analysis showed that these dynamic features predicted symptom severity above chance. The findings suggest a systematic bias in the temporal organization of whole-brain states at rest in MDD and indicate that this motor-dominant phenotype is clinically meaningful.

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