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Electroencephalogram alpha asymmetry in patients with depressive disorders: current perspectives

Authors Kaiser AK, Gnjezda MT, Knasmüller S, Aichhorn W

Received 22 December 2017

Accepted for publication 10 April 2018

Published 11 June 2018 Volume 2018:14 Pages 1493—1504

DOI https://doi.org/10.2147/NDT.S137776

Checked for plagiarism Yes

Review by Single-blind

Peer reviewers approved by Dr Andrew Yee

Peer reviewer comments 3

Editor who approved publication: Dr Roger Pinder

Andreas Kurt Kaiser,1 Maria-Theresa Gnjezda,1 Stephanie Knasmüller,1 Wolfgang Aichhorn2

1Department of Clinical Psychology, Salzburger Landeskliniken Betriebs-GesmbH, Christian-Doppler-Klinik, Paracelsus Medical University, Salzburg, Austria; 2Department of Psychiatry, Salzburger Landeskliniken Betriebs-GesmbH, Christian-Doppler-Klinik, Paracelsus Medical University, Salzburg, Austria

Purpose: Electroencephalogram (EEG) alpha asymmetry (AA) in depressive disorders has been of interest over the last few decades, but it continues to remain unclear whether EEG AA can discriminate between healthy and depressive individuals.
Materials and methods: A systematic literature search for papers addressing EEG AA using the keywords alpha asymmetry, depression, and EEG was performed in PubMed. All studies were checked for sample size, gender, handedness, reference, recording protocol, EEG band range, impedance, type of analysis, drugs, and comorbidity.
Results: A total of 61 articles were found, of which 44 met our inclusion criteria. They have been consecutively analyzed in respect of methodology and results. Approximately 25% (11/44) of the studies did not mention or ignored handedness, 41% (18/44) of the studies used data with only self-reported handedness, and only 34.1% (15/44) of all studies tested handedness. Only 35% (15/44) of the studies reported pharmacological treatment, and only 35% (15/44) of the studies controlled for medication. A total of 52% (23/44) of the studies reported comorbidity, and only 30% (13/44) of the studies controlled for comorbidity. Only 29.6% (13/44) of the studies reported education. In all, 30.5% (13/44) of the studies analyzed group differences and correlations, while 15.9 (7/44) of the studies used only correlational analyses. A total of 52.3% (23/44) of the studies analyzed only group differences. Alpha range was fixed (8–13 Hz) in 59.1% (26/44) of all studies. Reference to common average was used in seven of 44 studies (15.9%). In all, nine of 44 (20.5%) studies used the midline central position as reference, 22 of 44 (50%) studies used the ear or the mastoid as reference, and four of 44 (9.1%) studies used the nose as reference.
Conclusion: Discriminative power of EEG AA for depressed and healthy controls remains unclear. A systematic analysis of 44 studies revealed that differences in methodology and disregarding proper sampling are problematic. Ignoring handedness, gender, age, medication, and comorbidity could explain inconsistent findings. Hence, we formulated a guideline for requirements for future studies on EEG AA in order to allow for better comparisons.

Keywords: alpha asymmetry, depression, electroencephalogram, EEG, depressive disorders, review

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