Event related potentials to visual stimuli in patients with bipolar disorder before and after valproate monotherapy

Objectives: Cognitive dysfunction in bipolar disorder is evident. Event related oscillatory activity indicates integrative brain functioning.The study aimed to assess event related oscillatory activity in bipolar disorder before and after valproate monotherapy. We hypothesized that oscillatory responses would differ at different phases of illness and become closer to that of controls after treatment.Methods: Event Related Potentials (ERPs) to target stimuli in visual odd-ball paradigm in 10 manic/hypomanic, 10 euthymic, medication free patients were measured before and after six weeks of valproate monotherapy in comparison to healthy controls. Different frequency band responses were obtained by digital filtration of ERPs. Repeated measures ANOVA, Wilcoxon, Mann Whitney U and Pearson correlation tests were used for statistical analysis.Results: Manic patients showed significantly higher baseline occipital beta (18-30 Hz) responses than controls (p: 0.014) which reduced significantly (p: 0.009) after treatment. Patients were devoid of the occipito-frontal alpha (8-13 Hz) dominance presented by the controls. Only healthy controls displayed a significantly increased frontal alpha response at the second assessment. Post-treatment anterior temporal (p: 0.038) and occipital (p: 0.027) alpha responses were significantly lower than baseline. Euthymics had significantly higher baseline left frontal (p: =0.03) delta (0.5-3.5 Hz) response than controls. Frontal Fz (p: 0.04) F3 (p: 0.03), and temporal T3 (p: 0.02), T4 (p: 0.01), T5 (p: 0.01) delta responses decreased significantly after valproate.Conclusions: Bipolar patients show disturbed and different oscillatory response pattern at different phases of illness on which valproate shows a selectively corrective effect. This may be related to modulation of GABA/glutamate and valproate?s neuroprotective effect.