Neurofeedback for insomnia: Current state of research

Table 2 Summary of the results on surface neurofeedback

Ref.	Sleep outcomes measurements	Results
Schabus et al[45]	Objective: PSG; EEG; Subjective: PSQI; WHOQLA; SSS	Significant effect for NF compared to PF: (1) Higher SMR-power directly after each sessionb; and (2) Higher spindle density for the fast spindle type (C3 only)b; Significant effect for NF and PF: (1) Reduction of subjective sleep complaints after 12 sessionsb; and (2) Unspecific increase of physical quality of lifeb; Significant effect for INS compared to MP: (1) More wake timeb; and (2) Less stage 2, stage 3 and REMb; Significant effect for MP compared to INS: Higher SMR-power after each sessionb
Schabus et al[41]	Subjective: PSQI, Sleep Diary, WHOQLA, WMS-R, BSI	Significant effect only for NF: (1) Increase of SMR activity at C3a; (2) Decrease of the number of awakeningsa; and (3) Increase of stage 3a; Significant effect for NF and PF: (1) Reduction in subjective sleep complaintsb; and (2) Increased physical quality of lifeb
Cortoos et al[46]	Objective: PSG; Subjective: Sleep diary	Significant effect only for NF: (1) Decrease of SOLa and WASOa (Sleep diaries)a; and (2) Increased TSTa and SEa (Sleep diaries); Significant effect only for BF: Increase of SEa (Sleep diaries); Significant effect for NF and PF: (1) Decrease of SOLa and WASOa (PSG); and (2) Increase of REM sleep;
Arns et al[49]	Subjective: PSQI	Significant effect only for SMR: (1) Decrease of SOLd; (2) Decrease of SOL (40.1 min to 19.1 min)b; and (3) Correlation between the change in inattention and changes in PSQIb and SOLb; Significant effect for SMR + TBR: Decrease of SOL (25.8 min to 18.8 min)a
Sungwon[51]	Objective: EEG (resting state); Subjective: ISI, PSQI, DBAS	Significant effect only for NF: (1) Decrease of ISIb; (2) Changes in PSQIa; and (3) Decreased Beta power; Significant effect only for CBT-I: (1) Decrease of ISIa; (2) Changes in PSQIa; and (3) Decrease of DBASa
Shin[50]	Objective: EEG	Significant effect only for NF: Decreased spectral power for thetaa

^aP < 0.05.

^bP < 0.01, pre vs post.

^dP < 0.01 pre-treatment vs mid-treatment.

BF: Biofeedback; BSI: Brief Symptom Inventory; DBAS: Dysfunctional Beliefs and Attitude about Sleep; EEG: Electroencephalography; INS: Primary insomnia; MP: Insomnia misperception; NF: Neurofeedback; PF: Placebo neurofeedback; PSG: Polysomnography; PSQI: Pittsburgh Sleep Quality Index; REM: Rapid eye movement; TBR: Theta/Beta ratio; SE: Sleep efficiency; SOL: Sleep onset latency; SMR: Sensorimotor rhythm; SSS: Stanford Sleepiness Scale; WASO: Wakefulness after sleep onset; WHOQLA: World Health Organization Quality of Life Assessment; WMS-R: Wechsler Memory Scale – Revised.