Table 1.
Overview of existing experimental research addressing alpha NFT and its effects on behavioural measurements.
Fig 1.
Experimental procedure in NFT group (neurofeedback training, experimental group) and SF group (sham feedback, SF group) over four sessions on four consecutive days.
Fig 2.
Procedure within sessions S1 to S4.
Procedure during each of the sessions S1 to S4 in the NFT group (neurofeedback training, experimental group) and SF group (sham feedback, control group).
Fig 3.
Neurofeedback loop and EEG recording.
Fig 4.
Temporal development of individual upper alpha.
Temporal development of relative individual upper alpha over twenty 3-min periods of Neurofeedback Training (NFT, blue line) and sham feedback (SF, orange dashed line) during the four test sessions on four consecutive days. Relative alpha was obtained by dividing the average amplitude of the individual upper alpha band (around 10 to 13.5 Hz) by the average amplitude of the entire EEG band (i.e. 0.5 to 64 Hz). Moreover, relative alpha values was standardized with the first measurement (i.e. period 1). Error bars indicate standard error of the mean (SEM).
Fig 5.
Temporal development of short-term memory performance.
Temporal development of short-term memory (digit-span) performance over 8 tests (T1 to T8) in a neurofeedback (NFT, blue line) and a sham feedback (SF, orange dashed line) group. Subjects participated in four consecutive test days (S1-S4) containing two tests each. Uneven test numbers (T1, T3, T5 and T7) were conducted before the intervention (NFT or SF), even test number (T2, T4, T6 and T8) were conducted after the intervention. Error bars indicate SEM.
Fig 6.
STM performance before vs. after the intervention.
Short-term memory performance, measured by digit-span tests before and after neurofeedback training (NFT, blue line) and sham feedback (SF, orange dashed line). Error bars indicate SEM.
Fig 7.
Effects of neurofeedback training (NFT) on mood change.
A) Percentage of variance explained for each principal component (PC). The 5 PCs used result in a total of 60.2% of variance explained (dark-shaded bars). B) Loading matrix for each PC after Varimax rotation. Loadings smaller than 0.4 are not shown. C) Linear mixed effect model for PC5 as the response variable and the triple interaction between session, relative alpha an area under the curve with respect to increase (AUCi) and NFT group (neurofeedback training, experimental group) as predictors. D) Simple effects model for the NFT group. E) Simple effects model for the SF group (sham feedback, control group). For panels C), D) and E) coefficient estimates and standard errors (SE) depicted as dot and line respectively. Red and blue colors represent positive and negative coefficient estimates, respectively. Significance levels: ** p < .01, * p < .05. Significance levels are presented for uncorrected p-values. When Bonferroni correction is applied, to control for Type I errors due to the comparing models for five PCs, the triple interaction term in panel C is no longer significant (pcorrected = 0.152). For panels D and E, when applied, Bonferroni correction controls for two comparisons made in the simple main effects analysis resulting in a significant interaction effect ‘Session x relative alpha’ AUCi (pcorrected = 0.028).
Fig 8.
Linear mixed effect model for relative alpha area under the curve with respect to increase (AUCi) as the response variable and the interaction between how relaxed participants were at the beginning of the Session and NFT group (neurofeedback training, experimental group) as predictors.
Coefficient estimates and standard errors (SE) depicted as dot and line respectively. Red and blue colors represent positive and negative coefficient estimates, respectively. Significance levels: ** p < .01, * p < .05.
Fig 9.
Appearance frequency of words used by participants to describe their mental alpha enhancement strategy.
Frequency indicated by word size.