Complexity and variability analyses of motor activity distinguish mood states in bipolar disorder

Aims Changes in motor activity are core symptoms of mood episodes in bipolar disorder. The manic state is characterized by increased variance, augmented complexity and irregular circadian rhythmicity when compared to healthy controls. The aim was to characterize differences in motor activity when comparing manic patients to their euthymic selves. Methods Motor activity was collected from 14 bipolar inpatients in mania and remission. 24-h recordings and 2-h time series in the morning and evening were analyzed for mean activity, variability and complexity. Lastly, the recordings were analyzed with the similarity graph algorithm and graph theory concepts such as edges, bridges, connected components and cliques. Results When compared to euthymia, over the duration of approximately one circadian cycle, the manic state presented reduced variability, displayed by decreased standard deviation (p = 0.013) and augmented complexity shown by increased sample entropy (p = 0.025). During mania there were also fewer edges (p = 0.039) and more bridges (p = 0.026). Similar changes in variability and complexity were observed in the 2-h morning and evening sequences, mainly in the estimates of the similarity graph algorithm. A comparison of morning and evening sequences within states revealed no significant change in estimates for mania. Contrarily, the euthymic state showed significant evening differences in variance and complexity, displayed by fewer edges (p = 0.010) and an increased number of connected components (p = 0.009). Conclusion The motor activity of mania is characterized by altered complexity, variability, and circadian rhythms when compared within-subject to euthymia.