Alpha neurofeedback has a positive effect for participants who are unable to sustain their alpha activity

Abstract

Alpha rhythm (8-13 Hz) is linked to relaxed mental state in humans. Earlier reports have shown that individuals can increase their alpha power if provided with a valid feedback, compared to controls who are provided invalid feedback. However, these results remain controversial, partly because controls may be in a different behavioural state, making it difficult to directly compare their alpha power with the valid group. We here address this issue by using an experimental paradigm in which an invalid feedback is given on a fraction of trials, such that both valid and invalid conditions can be obtained from the same participant. Using EEG, we recorded alpha power from the occipital area from 24 humans (9 females) and played a feedback tone which could be valid (tone frequency proportional to alpha power), invalid (tone sequence from a previous valid trial; participants were unaware of this condition), or neutral (constant tone frequency). We found that during eyes closed-state, neurofeedback did not enhance alpha activity beyond pre-trained state within the experimental duration, probably because of saturation of alpha rhythmicity. However, for participants whose alpha power decreased over time within a trial, valid feedback helped them to sustain alpha more than invalid feedback. Further, alpha increase showed a weak negative correlation with their self-reported attentional load but was uncorrelated with relaxation levels. Our results reconcile many conflicting reports in the neurofeedback literature, and show that even under most stringent control, valid neurofeedback can help participants who are otherwise unable to sustain their alpha activity.

Significance Statement We tested whether providing a real time auditory feedback about the strength of the EEG alpha rhythm helps the participants increase their alpha power. Unlike previous neurofeedback studies that used valid and invalid feedback on different participant groups, we used a design in which valid, invalid and neutral feedback were given to the same participant. We found that for participants whose alpha power reduced over time within a trial, valid feedback helped to sustain the rhythm better than invalid feedback. Further, feedback appeared to be more useful for participants who did not attend the tone. These findings can be used to better screen and design neurofeedback training paradigm, which is now used to treat patients suffering from anxiety and depression.