Table 1.

Characteristics of the included studies (N = 10).

Reference, N (sex), medicated (yes/no)	Protocol, electrode position, number of sessions	Control group (yes/no), moment of measurement	Change in EEG-parameters investigated by	Behavioral change investigated by	Criterion established for EEG-learning (yes/no)	Results (1) Symptom change ↑ improvements (p < 0.05) <> = no change (2) Change in EEG-frequencies ↑ sign. increase in mean frequency ↓ sign. decrease in mean frequency <> = no change (3) Results concerning for EEG-learning
ADHD/ADD
Arns et al. (46), N = 21, ♂/♀, yes (some patients)	QEEG-Informed protocols: beta ↑/theta ↓/alpha ↓; or beta ↓; or SMR ↑/theta ↓ (+possibly alpha ↑); or SMR ↑; individual electrode position; mean number of sessions 33.62	No, pre-training, mid-training and post-training	Changes in power in IAF, SMR, beta frequency bands and ERP measures	MINI PLUS/MINI PLUS KID, BDI (inattention, hyperactivity/impulsivity, depression scores)	No	(1)Inattention ↑, hyperactivity/impulsivity ↑, depressive symptoms ↑. Response rate was 76% (16 out of 21) on behavioral measures (2)SMR power ↓, alpha, beta <>a
Mayer et al. (45); Mayer et al. (44),b N = 24, ♂/♀, yes	SCP ↓↑; Cz; 30 sessions	No, pre-, mid-, post-training and 6 months follow-up	Changes in CNV mean amplitude with Go/NoGo ERP task	ADHD-SB, WRI, FEA, FERT	Yes: learners/non-learners based on ability to differentiate between negativation/positivation in transfer condition of last 3 sessions	(1)Self-rated ADHD symptoms ↑, third-party rated ADHD symptoms ↑, depressive symptoms ↑, state and trait anxiety ↑, reaction time and reaction time variability ↑ (2)CNV showed a trend of increase over time (3)13 learners vs 11 non-learners. Trend toward larger improvements of self-rated ADHD symptoms in learners. Higher improvements of self-rated symptoms for learners at follow-upc
Schönenberg et al. (40), N = 113, ♂/♀, yes	Theta (4–8 Hz) ↓; beta (13–21 Hz) ↑; 30 sessions	Yes: sham-NFB/meta-cognitive group therapy (MCT), pre-training, mid-training, post-training and follow-up	Changes in mean theta/beta ratio	CAARS, BDI-II, STAI-state, FPTM-23, TAP, Stroop, CPT, INKA	No	(1)Inattention ↑, hyperactivity ↑, impulsivity ↑, anxiety symptoms ↑, depression ↑, TAP flexibility ↑, reaction time <>, no superiority of NFB as compared to control groups (2)Theta/Beta ratio <>d
Substance-use disorder
Arani et al. (18), N = 20, ♂, yes	Alpha (8–11 Hz) ↓/theta (5–8 Hz) ↑, after crossover alpha + theta ↑ while delta (2–5 Hz) ↓ at Pz; SMR (12–15 Hz) ↑ at Cz; 30 sessions	Yes: control group, no NFB, pre- and post-training	Changes in power of delta, theta, alpha, SMR, and high beta	SCL-90, HCQ	No	(1)SCL-90: somatization, obsession, interpersonal sensitivity, psychosis, hostility, total score ↑,e HCQ: anticipation for positive outcome, desire to use, relief from withdrawal ↑, intention and plan to use <> (2)Delta ↓ (central and frontal), theta ↓ (central area), alpha ↓ (parietal and frontal areas), SMR ↑ (frontal, central area)
Horrell et al. (47), N = 10, ♂/♀, no	SMR (12–15 Hz) ↑ at C3/theta (4–7 Hz) ↓ at F3; 12 sessions	No, pre- and post-training	Changes in mean amplitude of theta, SMR frequency and ERP measures	BDI-II (PTSS and depressions scores), PSS-R, cue reactivity test, drug testing	No	(1)Cue reactivity test: reaction time <>, accuracy <>, depression/stress ↑, drug testing: positive drug testing ↑a (2)SMR ↑ (mean increase 17%), theta <> Cue reactivity test: gamma responses to drug cues ↓
Lackner et al. (48), N = 25, ♂, yes	Alpha (8–12 Hz) ↑ at Pz; theta (4–7 Hz) ↑ at Fz; 12 sessions	Yes: TAU, pre- and post-training and 6 months-follow-up	Changes in absolute and relative band power for theta, alpha and beta frequency band	ACQ-R, BDI-V, BSI, FKV-lis, FPTM-23, PPR, SOC, perceived control over EEG, belief in efficacy of training	No	(1)No significant results for behavioral outcome measures posttreatment, perceived control of EEG ↑, belief in efficacy of training ↑ (2)Trend towards higher alpha, theta power ↑, beta <>f No significant effects found at follow-up
Schizophrenia
Gruzelier et al. (49), N = 25, ♂/♀, yes	SCP ↑↓; C3/C4; 10 sessions	No, improvements within and between sessions	Changes in self- regulation of interhemispheric negativity over course of training		Yes: good vs average performers based on visual inspection of performance in NFB-sessions, first 5 sessions vs last 5 sessions	(2)Ability of patients to learn self-regulation of interhemispheric negativity (3)Good performers had lateral shifts about twice as large as average performers (p < 0.058)a
Nan et al. (50), N = 1, ♀, yes	IAF ↑, beta 2 (20–30 Hz) ↓, 12.5 h in 4 days	No, pre and post-training	Mean relative amplitude in individual theta, alpha, sigma band, beta 1 (16–20 Hz)	Short-term memory test		(1)Memory↑ (2)Trend to increased IAB amplitude, trend toward decrease in relative beta 2 amplitudeg
Schneider et al. (14), N = 24, ♂, yes (patients only)	SCP ↑↓; Cz; 20 sessions for patients, 5 for health controls	Yes: two groups, both receiving NFB: schizophrenic patients Healthy controls, pre and post-training	Changes in mean differentiation of SCP over course of training		Yes: learning success defined as mean difference between required negativity increase and negative suppression	(3)Patients were less efficient in SCP self-regulation than controls, patients were only able achieve differentiation of feedback trials comparable to controls in the last three sessions of traininga
Psychopathy
Konicar et al. (27), N = 14, ♂	SCP ↑↓; Fcz; 25 sessions	No, pre- and post-training	Changes in mean differentiation of SCP for first 6 sessions vs last 6 sessions	FAF, BPAQ, BIS/BAS, Flanker Test	Learning investigated, but no criteria as to group patients	(1)Physical aggression ↑, behavioral approach ↑, reaction time ↑, commission errors ↑ (2)Increase in SCP differentiation, but not for transfer conditions (3)Learning progress over the whole 25 training sessions showed a significant increase of SCP differentiation for the feedback condition as well as for the transfer condition over timea

^aNo effect sizes given.

^bThe articles by Mayer et al. (44, 45) refer to the same study. Description is based on Mayer et al. (45).

^cCohens’d effect size d = 1.09.

^dEffect size within-participant 1:00 for NFB, 1:51 for sham, and 1:41 for mct.

^eEffect sizes for significant results on the SCL-90 η² ranged from 0.4 to 0.75. Effect sizes for HCQ ranged from η² = 0.32 to 0.45.

^fη² for absolute alpha 0.139, theta 0.111.

^gNo effect sizes given, forward digit test improved from 7 to 9, backward digit test improved from 5 to 6.

N, number of participants based on initial inclusion; IAF, individual alpha frequency; MINI/MINI KID, structured ADHD interview; BDI-(II–V), German version of Beck Depression Interview; ADHD-SB, Current ADHD questionnaire as part of HASE; WRI, ADHD Wender–Reimherr Interview; FEA, ADHD symptom questionnaire; FERT, questionnaire to assess expectancy with regard to treatment; CAARS, Conners’ Adult Rating Scale; STAI, Anxiety questionnaire; FPTM-23, Therapy Motivation Questionnaire; CPT, continuous performance test; INKA, inventory for complex attention; SCL-90, Symptom Checklist-90; HCQ-45, Heroin Craving Questionnaire; PSS-R, Posttraumatic Symptom Scale—Self Report; ACQ-R, Alcohol Craving Questionnaire Revised Form; BSI, Brief Symptom Inventory; PPR, Posttraumatic Growth Inventory; SOC, Sense of Coherence Scale; FAF, Assessment of aggressiveness factors; BPAQ, Buss–Perry Aggression Questionnaire; BIS/BAS, Behavior-Inhibition/Behavior-Activation System Questionnaire; ADHD, attention-deficit hyperactivity disorder; SCP, slow cortical potential; EEG, electroencephalographic; ERP, event-related potential; CNV, contingent negative variation; SMR, sensori motor rhythm.