title: Reduced long distance gamma (28-48 Hz) coherence in euthymic patients with bipolar disorder.
abstract: BACKGROUND
  EEG coherence represents the brain's functional connectivity. Synchronous neural gamma oscillations are critical for cortico-cortical communication and large-scale integration of distributed sets of neurons. We investigated long distance gamma (28-48 Hz) coherence in bipolar disorder.
  
  
  METHODS
  Sensory evoked coherence (EC) and event related coherence (ERC) values for the gamma frequency band during simple light stimulation and visual odd-ball paradigm was assessed in 20 drug-free euthymic bipolar patients in comparison to healthy controls. Groups were compared for the coherence values of the left (F(3)-T(3), F(3)-TP(7), F(3)-P(3), F(3)-O(1)) and right (F(4)-T(4), F(4)-TP(8), F(4)-P(4), F(4)-O(2)) intra-hemispheric electrode pairs by means of a repeated measure analysis of variance (ANOVA) and t-tests.
  
  
  RESULTS
  Patients showed significantly lower gamma coherence values in response to target stimuli than the healthy controls between left and right fronto-temporal, as well as between frontal and temporo-parietal electrode pairs. Coherence values for the non-target stimuli were significantly lower in the patients than the healthy controls between frontal and temporo-parietal regions on both right and left sides. EP coherence values did not differ significantly between the groups.
  
  
  CONCLUSIONS
  A relatively small sample size is the major limitation of the study.
  
  
  CONCLUSIONS
  Bipolar patients present disturbance in functional long-range connectivity between the frontal and temporal as well as temporo-parietal brain structures during a cognitive paradigm requiring attention and immediate recall. The location of the connectivity disturbance corresponds to the underlying neurobiology of executive function, memory and attention impairments in bipolar disorder and raises the question of whether gamma coherence reduction may be a candidate biomarker for bipolar disorder.
authors: Department of Psychiatry, Dokuz Eylul University Medical School, Izmir, Turkey. aysegul.ozerdem@deu.edu.tr
authors: Ayşegül
authors: A
authors: Özerdem
authors: Bahar
authors: B
authors: Güntekin
authors: Ilhan
authors: I
authors: Atagün
authors: Bilge
authors: B
authors: Turp
authors: Erol
authors: E
authors: Başar
mesh_terms: D000328:Adult; D000704:Analysis of Variance; D001714:Bipolar Disorder / Q000503:physiopathology*; D001921:Brain / Q000503:physiopathology*; D016022:Case-Control Studies; D003344:Cortical Synchronization; D003527:Cyclothymic Disorder / Q000503:physiopathology*; D004566:Electrodes; D004569:Electroencephalography; D005073:Evoked Potentials, Somatosensory; D005260:Female; D006801:Humans; D008297:Male; D010775:Photic Stimulation