Characteristics of Alpha Band Frequency in Adolescents ‎with Bipolar II Disorder: A Resting-State QEEG Study

Objective: The aim of this study ‎was to compare the QEEG of ‎adolescents affected by bipolar II ‎disorder with age and gender ‎matched healthy controls, and to ‎extract the characteristics of the ‎alpha frequency band to better ‎understand this disorder‏.‏ Methods: Twenty one ‎adolescents affected by acute ‎episodes of bipolar II disorder ‎‎(BMD II), both hypomanic and ‎depressive episodes, were ‎selected via convenience ‎sampling based on DSM IV ‎criteria and child and adolescent ‎psychiatrist diagnosis. Eleven ‎patients were going through a ‎hypomanic episode and 10 ‎patients were going through a ‎depression episode. Of the ‎participants, 18 who were ‎matched with the patient group ‎participated in this study as a ‎normal group. Any major ‎comorbidities and intellectual ‎disabilities were excluded ‎through applying K-SADS-PL and ‎Raven’s IQ test for all the patients ‎and the healthy participants. ‎Electroencephalogram signals ‎were obtained according to 10-20 ‎international system by 21 ‎electrodes from participants in ‎open and closed eyes in a resting ‎state. We selected 40 seconds ‎length segments from each ‎recorded EEG signals that had ‎minimal noise and artifacts. ‎Power spectrum density (PSD) ‎was estimated for each segment ‎and extracted alpha band ‎frequency. We used only ‎referential (unipolar) montage for ‎comparison. Eventually, data ‎were analyzed by independent ‎Mann-Whitney test and ‎independent t test‏.‏ Results: We observed significant ‎differences in the alpha ‎frequency band in some brain ‎regions. Alpha power increased ‎in the fronto-central region and ‎right parietal lobe in the patients ‎‎(P < 0.05). In the patients with ‎BMD II, entropy of alpha ‎oscillations was larger than the ‎normal participants in the central ‎region and in the F3, F4 and P4 ‎channels. Also, there were ‎differences in the variance of ‎alpha oscillations in these ‎regions between the two groups ‎‎(P < 0.05). In the occipital lobe, ‎alpha wave had different ‎skewness between the two ‎groups (P < 0.05).‎ Conclusion: Thalamus as a ‎generator and modulator of at ‎least a part of alpha oscillations ‎may be involved in this disorder ‎and hence this explains the ‎major symptoms like ‎distractibility and inattention in ‎both hypomanic and depressive ‎episodes of bipolar II disorder.‎