EEG Frontal Asymmetry in Unipolar and Bipolar Depression

Background: given the similarity of clinical manifestations of depressive disorder and depressive episodes within the framework of bipolar affective disorder, diagnostic errors are inevitable. Both overdiagnosis and underdiagnosis of bipolar affective disorder are too common, and it may take several years to establish a correct diagnosis. Despite the fact that it is impossible to completely eliminate diagnostic errors, it is important to reduce their likelihood by better understanding diagnostic criteria.

The aim of this study was to study the indicators of frontal EEG asymmetry in patients with unipolar and bipolar depression, as well as to identify possible correlations with the severity of clinical symptoms. Patients and methods: we examined 30 patients with affective disorder in the framework of a single depressive episode or recurrent depressive disorder and 30 patients with bipolar affective disorder, the current episode of mild or moderate depression. The bioelectric activity of the brain was recorded and analyzed with the calculation of the spectral power of beta and alpha rhythm in the frontal cortex and the beta/alpha ratio was calculated.

Results: it was found that patients with bipolar affective disorder had left-sided frontal asymmetry, the beta/alpha ratio was lower on the right than on the left (0.57 [0.41; 0.87] vs. 0.67 [0.43; 1.08], p = 0.007), while patients with unipolar depression had a bilateral pattern of frontal beta/alpha ratio (0.67 [0.45; 1.01] vs. 0.69 [0.45; 0.98], p = 0.441). Statistically significant negative associations were also found between the beta/alpha ratio in the right leads in patients with bipolar affective disorder and the duration of the disease (rs=–0.419, p=0.033).

Conclusion: the study clearly showed that quantitative EEG indicators can be used as an additional tool for differentiating bipolar and unipolar depression.

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