Reply: On assessing neurofeedback effects: should double-blind replace neurophysiological mechanisms?

Sir, We highly appreciate an open discussion regarding the effects of neurofeedback training (NFT), wherefore we are happy to respond to the letter by Fovet and colleagues, 2017. We agree that, strictly speaking, the results of our study (Schabus et al., 2017) do not allow generalizing the negative findings reported in primary insomnia to other NFT applications. Yet, what is disturbing is the fact that even misperception insomniacs (i.e. participants without any objectively quantifiable sleep problems) show unaltered EEG activity [in the same 12–15 Hz range; sensorimotor rhythm (SMR)] minutes after NFT sessions ended. At least we would have expected a sustained effect in this subgroup because they should not suffer from severe learning impairments. Surprisingly, these findings contradicted earlier reports from our own laboratory (Hoedlmoser et al., 2008; Schabus et al., 2014), where we added a healthy and younger control group and verified that participants achieved similar SMR enhancements during NFT training blocks (14–28%) as found earlier (15–25%; Schabus et al., 2014). Fovet and colleagues question how exactly these discrepancies between earlier (positive) results of our group in healthy participants (Hoedlmoser et al., 2008) and insomniacs (Schabus et al., 2017) are explained. First of all, it is important to note that in all three studies, we used exactly the same NFT methodology. The only exception was that we extended the NFT from 8 3 min to 8 5 min blocks (including two ‘transfer blocks’ with no immediate feedback) in the last double-blind study (Schabus et al., 2017). This was specifically done because we expected participants to have shallower learning curves due to the higher age [mean = 38.59, standard deviation (SD) = 11.18 in Schabus et al. (2017); mean = 34.83, SD = 10.60 in Schabus et al. (2014); mean = 23.63, SD = 2.69 in Hoedlmoser et al. (2008)] and the higher severity of insomnia [e.g. polysomnography (PSG)-derived wake after sleep onset 64.56 min in Schabus et al. (2017) versus 37.01 min in Schabus et al. (2014)]. So first of all, the slightly higher age may have rendered the observed effects in the latest study smaller than in the earlier two NFT studies. Second, we clearly highlight the non-optimal study design in our first insomnia study (2014), which was intended to serve as a comprehensive pilot test for the present and much more controlled double-blind study. Not only was that earlier study only single-blind but it also compared 10 blocks of NFT to five blocks of placebo-feedback (i.e. likewise randomized-frequency feedback). In an earlier study (cf. Fig. 6; Schabus et al., 2014), we reported a placebo effect on subjective quality of life across the sessions, i.e. an effect that was independent of whether participants received placebo or real neurofeedback; reanalysing the subjective data, we indeed found evidence that patients may have felt more social support in that earlier single-blind study in the NFT condition. This should be alarming for any neurofeedback study not adopting a double-blind design (cf. Fig. 1) as this effect is unlikely limited to our NFT study. Also, note that in this earlier study, we were unable to find an increase in sleep spindles or memory performance following NFT, contrary to what we had found in healthy doi:10.1093/brain/awx212 BRAIN 2017: 140; 1–5 | e64