The time-course of alpha neurofeedback training effects in healthy participants
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).
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Participants
Eighteen healthy right-handed participants (6 males and 12 females; M age = 20.7 years, 18–25, S.D. 1.79 years; Group A in Van Boxtel et al., 2012) were participated.
Design and procedure
The NFT sessions took place in a normal office room. All participants underwent 15 NFT sessions on consecutive working days. One training session always consisted of the same sequence of tasks: 5 min baseline with eyes opened (EO), 5 min baseline with eyes closed (EC), 5 min cognitive task, 8 min neurofeedback training (NFT1), 5 min
Results
In all analyses the fixed factor electrode was removed because the alpha power appeared not to differ between positions (F(1,290) = 0.97, p = 0.33).
Discussion
Clear indices of learning were observed with the novel NFT system. Alpha power increased both between and within training sessions. The results suggest that 10 training sessions are sufficient for this increase to develop, whereas the last 5 sessions did not result in further change. A similar pattern was found for training within a session; an increase from the first to the second training periods, and a decrease towards the end of the session. We interpret these results as time-on-tasks
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