title: EEG power, cordance and coherence differences between unipolar and bipolar depression.
abstract: BACKGROUND
  Understanding the biological underpinnings of unipolar (UD) and bipolar depression (BD) is vital for avoiding inappropriate treatment through the misdiagnosis of bipolar patients in their first depressive episode. One plausible way to distinguish between UD and BD is to compare EEG brain dynamics to identify potential neurophysiological biomarkers. Here we aimed to test group differences in EEG power, cordance and coherence values between UD and BD.
  
  
  METHODS
  Twenty-five bipolar and 56 unipolar depression patients were recruited. Sociodemographic and clinical variables were collected in addition to resting state EEG. Data was analyzed with multivariate and repeated analyses of variance where parametric assumptions were met.
  
  
  RESULTS
  Accordingly, we did not find any differences in the EEG absolute power and frontal asymmetry indexes between UD and BD. Regarding cordance, significant group differences were observed in the right theta cordance values (p=0.031). Regarding coherence, BD patients (as compared to UD) exhibited greater central-temporal theta (p=0.003), and parietal-temporal alpha (p=0.007) and theta (p=0.001) coherence. Lastly, less alpha coherence in BD was present at right frontal-central (p=0.007) and central inter-hemispheric (p=0.019) regions.
  
  
  CONCLUSIONS
  Our results demonstrate that EEG cordance and coherence values have potential to discriminate between UD and BD. The loss of temporal synchronization in the frontal interhemispheric and right sided frontolimbic neuronal networks may be a unique feature that distinguishes between BD and UD.
authors.affiliation: Department of Psychology, Uskudar University, İstanbul, Turkey; Division of Cognitive Neuropsychiatry and Psychiatric Preventative Medicine, Ruhr University, Bochum, NRW, Germany. Electronic address: cumhur.tas@uskudar.edu.tr.
authors.forename: Cumhur
authors.initials: C
authors.lastname: Tas
authors.affiliation: Department of Psychology, Uskudar University, İstanbul, Turkey.
authors.forename: Merve
authors.initials: M
authors.lastname: Cebi
authors.affiliation: Department of Psychology, Uskudar University, İstanbul, Turkey.
authors.forename: Oguz
authors.initials: O
authors.lastname: Tan
authors.affiliation: Department of Psychology, Uskudar University, İstanbul, Turkey.
authors.forename: Gokben
authors.initials: G
authors.lastname: Hızlı-Sayar
authors.affiliation: Division of Cognitive Neuropsychiatry and Psychiatric Preventative Medicine, Ruhr University, Bochum, NRW, Germany.
authors.forename: Nevzat
authors.initials: N
authors.lastname: Tarhan
authors.affiliation: Division of Cognitive Neuropsychiatry and Psychiatric Preventative Medicine, Ruhr University, Bochum, NRW, Germany; Maryland Psychiatric Research Centre, University of Maryland School of Medicine, Baltimore, MD, USA.
authors.forename: Elliot C
authors.initials: EC
authors.lastname: Brown
mesh_terms: D000328:Adult; D001714:Bipolar Disorder / Q000175:diagnosis / Q000503:physiopathology* / Q000523:psychology; D001921:Brain / Q000503:physiopathology*; D003865:Major Depressive Disorder / Q000175:diagnosis / Q000503:physiopathology* / Q000523:psychology; D003937:Diagnosis, Differential; D004569:Electroencephalography; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged
keywords: Coherence; Cordance; Depression; Electroencephalography; Hemispheric asymmetry; Power