Long distance gamma (28-48 Hz) coherence decreases under cognitive load in drug free euthymic patients with bipolar disorder

  • Professor Aysegul Ozerdem, Dokuz Eylul University Medical School, Turkey
  • Assistant Professor Bahar Guntekin, Istanbul Kultur University, Turkey
  • Ilhan Atagun, Bakirkoy Research and Training Hospital for Psychiatry, Neurology and Neurosurgery, Istanbul, Turkey
  • Bilge Turp, Brain Dynamics, Cognition, and Complex Systems Research Center University, Turkey
  • Assoc Professor Timucin Oral, Bakirkoy Research and Training Hospital for Psychiatry, Neurology and Neurosurgery, Turkey
  • Professor Erol Basar, Brain Dynamics, Cognition, and Complex Systems Research Center, Istanbul Kultur University, Istanbul, Turkey

Background: EEG coherence successfully measures brain’s functional connectivity. Synchronous neural gamma oscillations (30-80 Hz) are critical for cortico-cortical communication and large-scale integration of distributed sets of neurons. The aim of this study was to investigate long distance gamma (28-48 Hz) coherence under cognitive load in Bipolar disorder.
Methods: Fifteen DSM-IV euthymic bipolar I (n=13) or II (n=2) patients and 15 sex and age matched healthy controls were included in the study. Patients needed to be euthymic at least for four weeks and psychotrop free for at least two weeks. Gamma coherence in response to target stimulus during visual odd-ball paradigm was assessed. Inter-hemispheric F3-F4, T7-T8, TP7-TP8, P3-P4, O1-O2 and intra-hemispheric left (F3-T7, F3-TP7, F3-P3, F3-O1), and right sided (F4-T8, F4-TP8, F4-P4, F4-O2) electrode pairs were included in the analysis. Z scores of the coherence values were analysed by using Repeated measures ANOVA, and Mann Whitney U tests.
Results: Patients had lower mean gamma coherence z scores than that of healthy controls at all locations studied. However the difference was significant at left fronto-anterotemporal (F3-T7, p: 0.019), fronto-posterotemporal (F3-TP7, p: 0,019) and right fronto-posterotemporal (F4-TP8, p: 0.002) locations.
Conclusions: Bipolar patients present long distance fronto-temporal functional connectivity disturbance during an unsophisticated cognitive paradigm which involves attention and immediate recall. Finding points to neurobiological correlates of the wide range cognitive impairment that bipolar patients present even in euthymic phase of the illness.