Evidence for the efficacy of neurofeedback training (NF) of ADHD patients has been disputed by the most recent ADHD Current Care Guidelines in Finland.1 However, many recent research articles find at least tentative evidence for treatment efficacy, although emphasizing the complexity of NF learning. We argue that research on NF training should be continued, because it seems to benefit some patients, even if not all. The ability to identify in advance those who do actually benefit would greatly enhance the allocation of resources, and increase our understanding of ADHD itself.
ADHD is an increasingly common cause of young adults’ disability,2 but traditional treatment methods based on medication or behavioral therapy do not appear to address the core aspects of the disorder,3,4,5 or increase professional or academic performance.6,7
As one alternative treatment method, neurofeedback (NF) training aims to teach subjects to control the state of their own EEG function at various frequency bands. Namely electric activity in the brain occurs as waves with different frequencies, while each frequency band is associated with specific type of brain activity. By teaching subjects to control these brain waves it is believed that they could learn to self-regulate their own neurological activity.
The first attempts to apply the method specifically to inattentive and conduct-related symptoms emerged in the 1970s.8 This and subsequent work targeted the so-called sensorimotor rhythms (SMR), which are diminished during hyperkinetic behavior; and the theta and beta-rhythms (TB), for which training focuses on increasing beta waves involved in conscious thinking while at the same time decreasing theta-waves that are associated with diminished vigilance.
There is clear evidence for the efficacy of NF training in tackling ADHD. Several non-controlled trials concluded that NF treatment is at least as efficient as stimulant medication.9-12 In their meta-analysis, Arns et al13 conclude that NF training among children with diagnosed ADHD seems to moderately benefit those suffering from hyperactivity, and strongly benefit those suffering from impulsivity and inattention. The problematic question that remains is whether NF is specific, that is, whether the effects emerge from training itself or from other aspects of treatment. NF-related research thus faces both methodological and theoretical challenges.
Current Care Guidelines
Basing on a limited set of meta-analyses that address the specificity of its effects.14-16 ADHD Current Care Guidelines1 do not support the use of NF training on ADHD patients. Yet the significance tests of the previous meta-analyses could be biased by the small sample sizes of prior studies as well as non-standardised clinical practice. Moreover, the conclusion is even more controversial because at least one of the referred studies actually supports the use of NF training on inattentive symptoms,15 whereas in another meta-analysis the effect is almost statistically significant16 (SMD 0,29, 95 % confidence interval -0,02–0,61). Also Cortese et al14 conclude that differences in care practice affect results, since the three studies (which meet the standardisation criteria by Arns et al17) implicated a specific treatment effect.
Even if current, usually non-standardised forms of NF training cannot be recommended as a form of ADHD rehabilitation without reservations, there is both ethical18 and economic demand for new forms of treatment. In particular, the effects of medication require treatment to be continued over extended periods of time, whereas there is at least tentative evidence that the effects of NF training could be sustained over a longer term, even after termination of treatment. Therefore, NF-related research should not be discontinued despite the critical view of the Current Care Guidelines.
Why Current Research on NF Training of ADHD Patients is Limited?
The failure to establish the specificity of NF training could reflect the quality of research rather than NF training itself. The sample sizes are usually low, and studies often consider only the pre- and post-treatment measures rather than studying the entire training period. Even moderate effects would also be significant if they are sustained after the termination of treatment, unlike in standard stimulant-medication treatments where positive effects usually dissipate after termination of treatment.19 Finally, even if not all patients benefit specifically from NF training, some of them might do. Including all patients in the analysis would compromise the treatment effect visible among those patients who actually benefit.
Therefore, instead of taking the Current Care Guidelines at face value, we argue that research on NF training should continue, for the following reasons:
• ADHD patients should not be viewed as a uniform group, because different patients respond differently to each possible treatment.
• Learning processes associated with NF training should be studied more thoroughly in order to understand and improve the various NF training protocols.
• The role of human interaction in NF training should be given more attention.
Reason 1: Performers and Non-Performers
While most studies fail to distinguish between those do or do not benefit from NF training Ie. the so-called ‘performers’ and ‘non-performers’, recently a few studies have started to make this distinction.20 In fact, even a decade ago Doehnert et al21 found that only half of children in an NF study learned to self-regulate, and similar results have been confirmed in the context of alpha-training.22 However, the identification of ‘performers’ is strongly dependent on the chosen protocol.20 In fact, it is not even clear whether learning occurs similarly in different protocols. Future research should focus on those patients that do seem to benefit the most, to seek criteria to identify them in advance, and to further improve the effect of their NF training.
Reason 2: Learning Processes
NF learning has been viewed as being a form of operant conditioning where the subject learns to regulate the underlying EEG trait in a somewhat automatic fashion. In the operant conditioning model, ADHD is viewed as following from an abnormality in the EEG, and treatment aims to normalize the neurophysiological dysfunction.23 It is not always clear what is reinforced, however, because conditioning can also occur on the basis of more or less irrelevant behaviors during NF training such as breathing, eye movements or muscle activity.
Gevensleben et al24 contrast this ‘conditioning-and-repairing’ hypothesis with the so-called ‘skill-acquisition model’, which requires conscious effort and skill to change the EEG state.25 NF learning is then viewed as “a tool for enhancing specific cognitive or attentional states […]” irrespective of presumed neurophysiological deficits. This implies that motivational, attributional, and personality factors might play a stronger role.24 Strehl,26 in turn, attempts to bridge the two positions, arguing that both operant conditioning and conscious effort might be needed:20 as in Fitts’ theory of motor learning, where cognitive learning is a prerequisite for the successful automation of skills.
Most studies that have been critical towards the efficacy of NF training have ignored various aspects of the learning process. For example, Schönenberg et al27 presented a sham-controlled trial of NF (sham, equivalent to placebo in a drug trial, has long been cited as the required gold-standard of evidence for NF to provide proper blinding of subjects). However, their study employed an operant conditioning technique based on auto-thresholding, which has been heavily criticized by, e.g. Pigott et al.28 Such aspects have been thoroughly addressed by two empirical research projects that are also among the few existing empirical studies that seek to understand how NF-related skills might be transferred to real-life contexts.29,30
In future research, there should be more emphasis on the learning processes and particularly how NF-related skills can be transferred to other life contexts. A more thorough understanding of patient learning during NF training could also contribute to our understanding of ADHD itself.
Reason 3: Human Interaction
Also, in addition to the methodological challenges of studying success of NF learning, there might be various reasons for the failure to learn to self-regulate. These include psychological factors like “subjects’ beliefs regarding their ability to gain control over technological devices” and the lack of suitable mental strategies used in the learning process.31 Because psycho-education of such strategies and beliefs could enhance NF learning, it has been suggested that NF training itself could be viewed as a form of behavioral therapy,26 which has methodological implications for studying the efficacy of NF training that are ignored by most critics.24 Human engagement should be viewed as an important part of NF training, rendering it as a particular mode of behavioral therapy, and moving the discussion away from whether feedback of EEG signals alone has the claimed therapeutic effect, since such feedback cannot take place without a behavioural component (as also requested in Schönenberg et al’s32 response to Pigott et al’s28 criticism).
Existing evidence for the efficacy of NF training on reducing ADHD core symptoms is mixed and non-specific, with differing effect strengths for different NF protocols and even the different sub-types of ADHD. Future research on NF treatment must deal with three areas:
• Difference of performers and non-performers
• Learning processes
• The role of human engagement
On all grounds we find that the clinical guidelines should reflect the ongoing scientific debate over NF, and not presuppose a conclusion that is not yet supported.