Brain's alpha activity is highly reduced in euthymic bipolar disorder patients

Abstract

Brain's alpha activity and alpha responses belong to major electrical signals that are related to sensory/cognitive signal processing. The present study aims to analyze the spontaneous alpha activity and visual evoked alpha response in drug free euthymic bipolar patients. Eighteen DSM-IV euthymic bipolar patients (bipolar I n = 15, bipolar II n = 3) and 18 healthy controls were enrolled in the study. Patients needed to be euthymic at least for 4 weeks and psychotrop free for at least 2 weeks. Spontaneous EEG (4 min eyes closed, 4 min eyes open) and evoked alpha response upon application of simple visual stimuli were analyzed. EEG was recorded at 30 positions. The digital FFT-based power spectrum analysis was performed for spontaneous eyes closed and eyes open conditions and the response power spectrum was also analyzed for simple visual stimuli. In the analysis of spontaneous EEG, the ANOVA on alpha responses revealed significant results for groups (F(1,34) = 8.703; P < 0.007). Post-hoc comparisons showed that spontaneous EEG alpha power of healthy subjects was significantly higher than the spontaneous EEG alpha power of euthymic patients. Furthermore, visual evoked alpha power of healthy subjects was significantly higher than visual evoked alpha power of euthymic patients (F(1,34) = 4.981; P < 0.04). Decreased alpha activity in spontaneous EEG is an important pathological EEG finding in euthymic bipolar patients. Together with an evident decrease in evoked alpha responses, the findings may lead to a new pathway in search of biological correlates of cognitive impairment in bipolar disorder.

Keywords: Bipolar disorder; EEG alpha activity; Euthymia; Schizophrenia; Visual evoked alpha oscillations.

Fig. 1

Grand averages of power spectra of 18 healthy and 18 euthymic subjects for the eyes open recording session for occipital locations. The black line represents the grand average of power spectra of evoked response in healthy subjects. The red line represents the grand average of power spectra of evoked response in euthymic subjects

Fig. 2

Grand averages of power spectra of 18 healthy and 18 euthymic subjects for the eyes closed recording session for occipital locations. The black line represents the grand average of power spectra of evoked response in healthy subjects. The red line represents the grand average of power spectra of evoked response in euthymic subjects

Fig. 3

Grand averages of power spectra of evoked response in 18 healthy and 18 euthymic subjects in the alpha frequency range upon application of simple light stimuli for occipital locations. The black line represents the grand average of power spectra of evoked response in healthy subjects. The red line represents the grand average of power spectra of evoked response in euthymic subjects

Fig. 4

a Mean alpha power values of 18 healthy and 18 euthymic patients in eyes open recording session. b Mean alpha power values of 18 healthy and 18 euthymic patients in eyes closed recording session. c Mean visual evoked alpha power values of 18 healthy and 18 euthymic patients upon application of simple light stimuli. The mean alpha power spectrum values of healthy subjects are represented by black bars; the mean alpha power spectrum values of eutyhmic subjects are represented by gray bars