The time-course of alpha neurofeedback training effects in healthy participants

Highlights

• Clear indices of learning were observed with the novel NFT system of Van Boxtel et al. (2012).

• Results suggest that 10 training sessions are sufficient for a significant increase in alpha power to develop.

• Thereafter, it seems that the participants grew tired and could not sustain attention.

• Learning indices were different for the lower and upper alpha bands.

• Upper alpha power decreased at the end of training, whereas the lower alpha band did not.

Abstract

The time-course of alpha neurofeedback training (NFT) was investigated in 18 healthy participants who received 15 sessions of training (eyes open), each consisting of three training periods (data are from Van Boxtel et al., 2012). Here we report on the within- and between-session training effects using multilevel analyses. Over sessions, total alpha power (8–12 Hz) increased up to the tenth session, after which low alpha power (8–10 Hz) remained at the same level, while high alpha power (10–12 Hz) decreased. Within each training session, total alpha power increased from the first to the second period, and then decreased again. This decrease, however, was caused by a decrease in high alpha power only; low alpha power remained up to the end of training. These effects are discussed in terms of attention and motivation, and suggest different trainability for low and high alpha power.

Introduction

In a recent study, Van Boxtel et al. (2012) introduced a novel neurofeedback training (NFT) system based on a commercially available audio headset with water-based electrodes mounted in the band between the ear-pads. They tested the system in healthy participants who received alpha (8–12 Hz) training in 15 daily sessions while listening to their favourite music, of which the quality was adapted as a function of the alpha power. Each session consisted of three 8-min periods of NFT, interspersed with cognitive tasks, intended to prevent the participants from falling asleep while at the same time allowing the study of the effects of alpha training on cognition. Total alpha power was indeed increased after training. Interestingly, a further increase was observed in a 3 month follow-up measurement without further training. The training appeared to be self-guided in that participants received no instructions and still managed to increase the alpha power.

Here we report on the learning effects of the alpha NFT in that study. We wanted to know how alpha training progressed over sessions, but also between the three training periods within a single training session. If alpha power over sessions would reach an asymptote, this would suggest that the number of training sessions was appropriate or could be lower. In clinical applications individuals often need repetitive sessions (20–60) for clear effects to occur at late stages of training (e.g., Ros & Gruzelier, 2010). Non-clinical applications often use fewer sessions (1–30; e.g., Myers and Young, 2011, Ros and Gruzelier, 2010, Vernon, 2005), and we wanted to make sure that 15 sessions were appropriate. Analysing the training data allowed us to check whether the design choices were appropriate, while at the same time demonstrating that learning actually occurred.

In the original report (Van Boxtel et al., 2012) only total alpha power was analysed. However, as lower and upper alpha bands may be differentially involved in selective attention (e.g., Klimesch et al., 1990, Klimesch et al., 2007) and cognitive processing (e.g., Doppelmayr et al., 2005, Zoefel et al., 2010), we analysed lower (8–10 Hz) and upper (10–12 Hz) alpha bands separately. It is largely unknown whether lower and higher alpha bands differ in trainability, but a few isolated studies suggest that this may be the case (Aftanas and Golocheikine, 2001, Bazanova, 2012).