Cortical functional connectivity features between bipolar and unipolar depression patients

Abstract

Objective To explore the differences of cortico-cortical functional connectivity features among patients with bipolar and unipolar depression in resting-state. Methods Whole-head magnetoencephalography scan was performed in an resting-state condition in 12 bipolar depression patients, 27 unipolar depression patients and 21 gender-, age-, level of education-matched healthy controls. The strength of cortico-cortical functional connections was measured with synchronization likelihood (SL) value, and the SL value of long-rage as well as short-rage within θ, α1, α2, β and γ frequency bands were compared in three groups. Group-wise two post-hoc t-test was performed according to the results of ANOVA. Results Compared with the unipolar depression patients and the controls, bipolar patients showed increased local θ (0.249±0.087, 0.181±0.029, 0.196±0.032; F=8.511,P=0.001); α1(0.200±0.051, 0.164±0.020, 0.175±0.028; F=5.292, P=0.008) and α2 (0.200 ± 0.047, 0.175±0.025, 0.183±0.025; F=4.721, P=0.013) SL in the left occipital lobe and local β (0.186±0.027, 0.166±0.024, 0.159±0.026; F=4.195, P=0.020) and γ (0.151±0.020, 0.128±0.019, 0.133±0.019; F=5.521, P=0.006) SL in right frontal lobe. Compared with the controls, the bipolar patients presented increased β (0.076±0.013 vs. 0.087±0.011, P=0.009) and γ(0.062±0.010 vs. 0.069±0.010, P=0.020) inter-hemispheric SL between bilateral frontal lobe, whereby the unipolar patients showed decreased γ(0.057 ± 0.013 vs. 0.050 ± 0.005, P=0.009) band inter-hemispheric SL in the right frontal-parietal regions. Conclusions The bipolar depression patients displayed further dysfunction of cortical resting connectivity over the fronto-parieto-occipital regions than unipolar depression patients. The loss of temporal synchronization in the frontal and occipital lobe may be a biomarker to differentiate bipolar from unipolar depression. Key words: Bipolar disorder; Depressive disorder; Manetoencephalography; Synchronization likelihood; Functional connectivity