The Do's and Don'ts of Neurofeedback Training: A Review of the Controlled Studies Using Healthy Adults

Abstract

The goal of EEG neurofeedback (EEG-NFB) training is to induce changes in the power of targeted EEG bands to produce beneficial changes in cognitive or motor function. The effectiveness of different EEG-NFB protocols can be measured using two dependent variables: (1) changes in EEG activity and (2) behavioral changes of a targeted function (for therapeutic applications the desired changes should be long-lasting). To firmly establish a causal link between these variables and the selected protocol, similar changes should not be observed when appropriate control paradigms are used. The main objective of this review is to evaluate the evidence, reported in the scientific literature, which supports the validity of various EEG-NFB protocols. Our primary concern is to highlight the role that uncontrolled nonspecific factors can play in the results generated from EEG-NFB studies. Nonspecific factors are often ignored in EEG-NFB designs or the data are not presented, which means conclusions should be interpreted cautiously. As an outcome of this review we present a do's and don'ts list, which can be used to develop future EEG-NFB methodologies, based on the small set of experiments in which the proper control groups have excluded non-EEG-NFB related effects. We found two features which positively correlated with the expected changes in power of the trained EEG band(s): (1) protocols which focused on training a smaller number of frequency bands and (2) a bigger number of electrodes used for neurofeedback training. However, we did not find evidence in support of the positive relationship between power changes of a trained frequency band(s) and specific behavioral effects.

Keywords: EEG; methodology; neurofeedback training; protocol efficacy; replicability.

Figure 1

(A) Schematic representation for article selection. (B) Schematic representation of the experiments used in the review. Dark gray boxes specify the experimental paradigms grouped for analytical studies according to EEG (left branch) or behavioral protocol (right), light gray boxes specify groups not included in the analyses. In the EEG protocols branch, N denotes the number of experiments included in each EEG and behavioral group (EEG/behavioral) where EEG effects (changes of the EEG spectrum) were analyzed. In the Behavioral goals branch N denotes the number of experiments in each behavioral or cognitive group. The 28 EEG-NFB experiments were used for analyses. Of these studies, smaller groups were defined according to their specific EEG training protocols or the expected behavioral/cognitive effects. The groups are not mutually exclusive; both types of data were often analyzed in the same study, which resulted in multiple classifications. Some experiments also investigated more than one behavioral goal (Table 4). Protocols that could not be attributed to any of the specific subgroups (lowermost boxes “Other”) contributed only to the general analysis.

Figure 2

Success ratio of the spectral EEG changes (dark gray bars) and behavioral improvement (light gray bars) calculated for: (A) experiments grouped according to training with particular frequency band protocols and (B) training aimed at different behavioral effects (i.e., improvement in attention and memory). Only protocols used in five or more experiments are included in the graphs with exception to four behavioral experiments in the Beta Group designated by ^*.