Power Spectral And Functional Connectivity Analysis On Major Depressive Disorder: A Resting MEG Study

Objectives （1） To explore the discrepancies of Magnetoencephalography（MEG）spectral power between female patients with major depressive disorder （MDD）andnon-depressed comparison subjects in resting state.（2） To investigate the changes ofresting MEG spectral power of patients with MDD for the antidepressant treatmentresponse.（3） To examine the difference of individualized frequency and band powerbetween MDD and controls in resting state, and link the abnormal spectral power toclinical severity of MDD.（4） To investigate the cortico-cortical functionalconnectivity abnormalities of MDD on MEG recordings in the resting state usingsnchronization likelihood （SL）; further more, to explore whether the modifications ofanomalous functional coupling could be correlated with disease severity of depressivepatients as expressed by HAMD score.Methods Major depressed patients, which met with CCMD-3and DSM-IV-TRdiagnosis criteria, and matched healthy controls were recruited. All the participantswere underwent resting MEG scanning and HAMD₁7examination. The patients witheffective treatment after8-16weeks were managed to the second scanning.Discrepancies between groups were obtained by two sample t-test or permutation testusing MATLAB7.8.Results （1） Compared to the controls, depressed patients showed increased alphaactivity of the right parietal lobe and increased beta activity of the bilateral parietaland the occipital lobes, while the power of theta and delta frequency was decreased in the right temporal and the left occipital lobes, respectively.（2） Decreased delta powerin the left frontal lobe, and diminished theta power in the bilateral occipital of MDDstill existed after treatment. The power of theta frequency band in the left occipitallobe and the left central regions was decreased in patients group after treatmentcompared to the prior-treatment, the same situation was also occurred in the power ofalpha band frequency in the left central region.（3） The results of individual frequencyband were revealed as follows: lower alpha2and upper alpha of the right frontal lobewere decreased in MDD, also with a decreased theta power in the right temporal lobe.MDD showed an increased beta activity of the bilateral occipital and the right parietallobe, and enhanced slower alpha1power of right occipital. A positive correlation wasobserved between the right occipital lower α1band power and HAMD₁7score fordepression（r=0.51, P=0.03）.（4）MDD patients displayed a widespread inefficientpattern of functional coupling on all frequencies, mainly affected long and shortdistance in the fronto-temporal, the fronto-parietal and the parieto-occipital sensorpairs in the lower （theta and alpha） frequency bands. By contrast, the soleincreasement of synchronization existed in the left central area of beta band.Intrahemispheric SL value of fronto-parietal on alpha1frequency was negativecorrelated with disease severity.Conclusions （1） The discrepancies of spectral power show a predominance inposterior brain areas involving delta, theta, alpha and beta frequency bands indepressed patients in comparison with non-depressed comparison subjects.（2） Thepower of alpha and beta frequency bands of MDD was improved after the treatment,while significant difference was still existed in the slow wave activity of depressedpatients compared in comparison with normal subjects.（3） The results support theview that patients had a disorganized limbic-cortical activation and an inefficientinhibition function, which may contribute to the emotion disturbance of MDD. The power of lower α1of the right occipital lobe was considered to be a clinical indicatorof depression severity.（4）Present results indicated that patients of MDD exhibit anadynamic state in information transmission among cortical regions in restingcondition, which may be a reflection of impaired “top-down” cognitive function inMDD. Decreased right fronto-parietal connectivity in the8-10Hz range seems to beconsiderable to estimate depression severity.