Altered Complexity of Spontaneous Brain Activity in Schizophrenia and Bipolar Disorder Patients.

BACKGROUND Schizophrenia (SC) and bipolar disorder (BP) share elements of symptoms and the underlying neural mechanisms for both remain unclear. Recently, the complexity of spontaneous functional MRI (fMRI) signals in brain activity has been investigated in SC and BP using multiscale sample entropy (MSE) with inconsistent results. PURPOSE To perform MSE analysis across five time scales to assess differences in resting-state fMRI signal complexity in SC, BP, and normal controls (NC). STUDY TYPE Retrospective. POPULATION Fifty SC, 49 BP, and 49 NC. FIELD STRENGTH/SEQUENCE A 3 T, T2* weighted echo planar imaging (EPI) sequence. ASSESSMENT The mean MSEs of all gray matter (GM) and of 12 regions of interest (ROIs) were extracted using masks across the five scales. The regional homogeneity (ReHo) and amplitude of low-frequency fluctuation (ALFF) in these ROIs were also determined and the relationship between the three measures was investigated. The correlations between cognitive assessment scores and MSE values were also explored. STATISTICAL TESTS Bonferroni correction, One-way ANOVA, Spearman rank correlation coefficient (r), Gaussian random field (GRF) correction. RESULTS There were decreased GM MSE values in the patient groups (F = 9.629, P   0.282, P   0.278, P < 0.05). Furthermore, median temporal MSE (r = -0.321, P < 0.05) on scale 3 and (r = -0.307, P < 0.05) on scale 4 and median cingulate MSE (r = -0.337, P < 0.05) on scale 5 was significantly negatively correlated with cognitive assessment scores. DATA CONCLUSION These data highlight different patterns of brain signal intensity complexity in SC and BP. LEVEL OF EVIDENCE 1 TECHNICAL EFFICACY: Stage 1.