Functional role of frontal electroencephalogram alpha asymmetry in the resting state in patients with depression: A review

Table 1 The comparison of methods in studies on asymmetry pattern at resting state of clinically depressed individuals

Ref.	Sample		Age (yr)		% female	Diagnosis of depression	EEG detail
	Experimental group	Control group	Experimental group	Control group			Reference montage	EO/EC	Recording length (min)	Alpha range (Hz)
Henriques et al[20], 1991	EG: 15 depressed subjects	CG: 13 healthy controls	M = 40.40 (depressed subjects)	M = 40.61 (HCs)	60.7	SADS	CZ; AE; AR	E0+EC	1	8–13
Baehr et al[21], 1998	EG: 13 MDD	CG: 11 healthy controls	M = 43.50 (MDD)	M = 44.20 (HCs)		DSM-IV; BDI	Cz	EC	5	8–13
Beeney et al[22], 2014	EG: 13 MDD	CG: 21 healthy controls	M = 32.12 (MDD)	M = 27.78 (HCs)	100	DSM–IV; SCID	AL	E0+EC	8	8–13
Bruder et al[23], 1997	EG: 44 MDD (19 with and 25 without an anxiety disorder)	CG: 26 healthy controls	MDD with an anxiety disorder: M = 36.70; MDD without an anxiety disorder: M = 41.30	M = 32.90 (HCs)	50	DSM-III-R	NR	E0+EC	6	7.8–12.5
Cantisani et al[24], 2016	EG: 20 depressed subjects	CG: 19 healthy controls	M = 43.30 (depressed subjects)	M = 41.05 (HCs)	53.8	SCID; DSM-IV-TR	CA		6	8–12.5
Dharmadhikari et al[25], 2019	EG: 24 MDD	CG: 17 healthy controls	M = 34.82 (MDD)	M = 29.52 (HCs)	63.4	DSM-IV	auricle	EC	10	8--13
Gordon et al[26], 2010	EG: 92 MDD	CG: 1908 healthy controls			58.7	DSM-IV	AR	E0+EC	4	8–13
Gotlib[27], 1998	EG: 16 currently depressed, 31 previously depressed	CG: 30 never depressed				SCID	Cz	E0+EC	8	8–13
Jaworska et al[28], 2012	EG: 53 MDD	CG: 43 healthy controls				DSM-IV-TR; SCID-IV-I/P; HAMD; MADRS	AM; CZ; AR	E0+EC	6	8–13
Kemp et al[29], 2010	EG: 15 MDD	CG: 15 healthy controls	M = 39.90 (MDD)	M = 42.40 (HCs)	60	MINI; DASS	AM	EC	2	8–13
Koo et al[30], 2019	EG: 20 MDD	CG: 20 healthy controls	M = 51.05 (MDD)	M = 47.15 (HCs)		ICD-10/DSM IV	AE	EC	10	8–13
Roh et al[31], 2020	EG: 44 MDD without Suicidal ideation, 23 MDD with suicidal ideation	CG: 60 healthy controls	M = 39.30 (MDD); M = 37.48 (MDD with SI)	M = 34.83 (HCs)	85	DSM-IV	ECC	EO	3	8–12
Stewart et al[32], 2010	EG: 143 MDD	CG: 163 healthy controls	M = 19.10 (MDD)		69	DSM-IV	CSD; Cz; LM	E0+EC	8	8–13
Cai et al[34], 2020	EG: 24 MDD	CG: 22 healthy controls				DSM-IV; MINI	Cz	EC	5	8–14
Nusslock et al[35], 2018	EG: 37 depression, 18 anxiety + depression	CG: 69 healthy controls				SCID	AM	E0+EC	6	8–13
Brzezicka et al[36], 2017	EG: 26 MDD	CG: 26 healthy controls	M = 28.00 (MDD)	M = 24.90 (HCs)			CSD	EC	5	8–13
Jang et al[37], 2020	EG: 20 MDD, 18 patients with schizophrenia	CG: 16 healthy controls	M = 42.60 (MDD); M = 32.00 (MDD with schizophrenia)	M = 37.75 (HCs)	48.1	DSM-IV; MINI	BM	E0+EC	5	8–12
Segrave et al[38], 2011	EG: 16 MDD	CG: 18 healthy controls	M = 40.75 (MDD)	M = 42.11 (HCs)	100	DSM-IV	Cz; CA	E0+EC	6	8–13
Quinn et al[39], 2014	EG: 117 MDD	CG: 120 healthy controls				MINI; DSM-IV	AR; ER	EC	2	8–13
Smith et al[99], 2018	EG:143 lifetime MDD, 62 current MDD	CG: 163 healthy control			69	BDI; SCID	Cz	E0+EC	8	8–13
Vuga et al[40], 2006	EG: 49 childhood onset MDD	CG: 50 healthy controls	19-34	19-39	66.7	DSM-IV	Cz	E0+EC	6	7.5–12.5; alpha 1 (7.5–10.5); alpha 2 (10.5–12.5)
Gold et al[41], 2013	EG: 79 adults with depression		M= 35.60		78.5	DSM-III-R; SCID; MADRS	ALM	EC	5	8–12
McFarland et al[42], 2006	EG: 67 MDD		M = 34.64		65.7	SCID	LE	E0+EC	6	8–13
Kentgen et al[44], 2000	EG: 25 right-handed female outpatients	CG: 10 healthy controls			100	DSM-IV	NR	E0+EC	6	7.8--12.5
Feldmann et al[45], 2018	EG: 16 adolescents with depression	CG: 34 healthy controls	M = 16.08	M = 15.67	72.6	ICD-10; BDI	Cz; Mastoids; AE	E0+EC	8	7.5–13
Grünewald et al[46], 2018	EG: 20 adolescents (12–17 yr) with unipolar depression (12 with fifirst episode, 8 with recurrent depression)	CG: 31 healthy controls	M = 14.85 (unipolar depression)	M = 14.16 (HCs)	60.8	DSM-IV; ICD-10	AR		5	7.5–13.5
Deslandes et al[89], 2008	EG: 22 depressed subjects	CG: 14 healthy controls	M = 71.60 (depressed subjects)	M = 72.40 (HCs)	94	DSM-IV	ER	E0+EC	8	8–13
Kaiser et al[50], 2018	EG: 14 depression, 11 anxiety + depression	CG: 14 healthy controls	M = 78.60 (anxiety + depression); m = 80.50 (depression)	M = 80.90 (HCs)	100	GDS; HADS	RLMB	E0+EC	4	6.9–12.9
Carvalho et al[51], 2011	EG: 12 depressed subjects, 8 remitted subjects	CG: 7 non-depresse elderly subjects			66.7	DSM-IV	Earlobes	EC	8	8–12.9

EC: Eyes closed; EO: Eyes open; EEG: Electroencephalogram; HCs: Healthy controls; MDD: Major depressive disorder.

Diagnosis of depression: BDI: Beck Depression Inventory; DASS: Depression, Anxiety and Stress Scales; DSM-IIIR: Diagnostic and Statistical Manual of Mental Disorders, Third edition, Revised; DSM-IV: Diagnostic and Statistical Manual of Mental Disorders, Fourth edition; GDS: Geriatric depression scale; HAMD: Hamilton Rating Scale for Depression; HADS: Hospital anxiety and depression scale-depression; ICD-11: 11^th edition of the International Classification of Diseases; MADRS: Montgomery and Asberg Depression Rating Scale; MINI: Mini International Neuropsychiatric Interview; SADS: The Schedule for Affective Disorders and Schizophrenia; SCID: Structured Clinical Interview for DSM IIIR; SCID-IV-I/P: Structured Clinical Interview for DSM-IV, Axis I, Patient Version.

Reference montage: AE: The average across all 31 electrodes; AL: The average of all EEG leads; ALM: Averaged linked mastoids; AM: Averaged mastoids; AR: Average reference; BM: Both mastoids; CA: Common average montage; CA: Common average; CSD: Current source densities; ECC: The reference electrode was predefined; ER: Ear reference; LE: Linked ear; LM: Linked mastoids; NR: Nose reference; RLMB: The right and left mastoid bone.