It has long been a widely held belief that the brain once developed into adulthood, is an anatomically and physiologically static organ. In early childhood, critical periods of development were thought to exist in which the brain may undergo important changes, as was, for instance, demonstrated by Hubel and Wiesel (1970) for ocular dominance columns, but pathways were considered to be fixed once firmly established. Changes to the brain were only possible in very specific areas of the brain such as the cerebellum and hippocampus by environmental changes (learning). In the beginning of the 1980s, researchers began to develop different views, and evidence became available that the brain possessed self-organising principles, such as after differentiation of peripheral nerves (e.g. Merzenich & Kaas, 1982). This self-organising principle of the brain is now beyond doubt and has become known as neuroplasticity or brain plasticity. Anatomy aside, evidence that the electrophysiology of the brain can be influenced, predates the above findings by nearly half a century.
Neurofeedback entails learning to self-control brain activity largely based on operant conditioning principles, with the aim of improving mental states or processes, whether or not in clini- cal conditions. The finding that the human electroencephalogram (EEG) was susceptible to classical conditioning principles dates back to the 1930s (Durup & Fessard, 1935; Loomis, Harvey, & Hobart, 1936; Jasper & Shagass, 1941), and operant conditioning principles were first applied to the EEG in the 1960s (Kamiya, 1962; Nowlis & Kamiya, 1970; Sterman, Wyrwicka, & Roth, 1969). Ini- tial work on clinical application of neurofeedback was the most developed in the field of attention disorders such as ADHD (Lubar & Shouse, 1976; Elbert, Rockstroh, & Birbaumer, 1984; see Arns & Kenemans, 2013, for a recent review and a theoretical perspective). However, the field of neurofeedback has long been surrounded by an aura of mystery and sceptical antagonism that have hindered progress. Various factors, such as some failed replications, absent or poor control conditions in some early studies, insufficient insight into underlying mechanisms, overstatement of clinical benefits and premature popularisation in society at large, all may have con- tributed to a certain caution in the adoption of neurofeedback as a research theme by university laboratories.
This is now rapidly changing. The last decade has witnessed a sharp rise in the number of publications about neurofeedback (Fig. 1), and this can be interpreted as a sign that an increasing number of research groups are now recognising neurofeedback as a research topic. This seems to be especially the case in European university centres. Advances in technology have greatly simpli- fied the recording of the EEG, so that researchers could focus on more advanced topics, could use and develop more sophisticated research designs, and could apply the neurofeedback methods to a variety of clinical groups. These developments allowed the neu- rofeedback field to mature to where it is now, and this Society of Applied Neuroscience special issue is aimed at providing an overview of the current state of the field.
The Society of Applied Neuroscience (SAN, http://www.applied- neuroscience.org) was established in Europe as an international society to investigate the potential of neurofeedback, to pro- mote research on validation and to encourage cross fertilisation in applied neuroscience. This special journal issue is one of four, an initiative encouraged by Elsevier, which is a themed issue on neurofeedback at the journal editor’s invitation. The three others focus on applied neuroscience, one of which consists of theoret- ical and methodological aspects in the journal Neuroscience and Biobehavioural Reviews, and the other two issues are collections of empirical papers on psychobiology and on development and pathology published in the International Journal of Psychophysi- ology.
Here the focus is mainly on non-clinical applications of neu- rofeedback. Some research laboratories have started using novel techniques that go beyond conventional EEG measurements as input for the feedback process. Especially topographical infor- mation is thought to increase the specificity of neurofeedback techniques. Ruiz, Buyukturkoglu, Rana, Birbaumer, and Sitaram (2014) eloquently review the use of functional magnetic reso- nance imaging (fMRI) in neurofeedback, focussing on functional connectivity between different brain areas. Near-infrared spectog- raphy (NIRS) is used by Kober, Wood, Kurzmann, Friedrich, Stangl, Wippel, Väljamäe, and Neuper (2014) to increase motor-related brain activity, aimed at training patients with focal brain lesions. But even in conventional EEG, topographical information can be increased using techniques such as LORETA, as Maurizio, Liechti, Heinrich, Jäncke, Steinhausen, Walitza, Brandeis, and Drechsler (2014) beautifully demonstrate in the first controlled tomographic study into ADHD.
A second set of articles deals with EEG neurofeedback in improv- ing various aspects of human cognitive performance in non-clinical samples. Reiner, Rozengurt, and Barnea (2014) show that a single session of theta (4–7 Hz) neurofeedback, relative to beta (12–15 Hz) neurofeedback and control groups, increased motor performance in a finger tapping-task. A night’s sleep further improved perfor- mance, as has been found before, but only theta training led to further increases in performance, even lasting as long as a week. In a similar vein, a single session of mu (8–12Hz) suppression neurofeedback over the motor cortex was shown to speed up the acquisition of a procedural learning task by Ros, Munneke, Parkinson, and Gruzelier (2014). Interesting findings such as these cry out for further investigations in applied settings such as elite sports. Using frontal midline theta (4–8 Hz) activity and an ade- quate active control condition, the paper by Enriquez-Geppert, Huster, Scharfenort, Mokom, Zimmermann, and Herrmann (2014) provides information on how such training protocols can be indi- vidualised, and on how training progresses from session to session. The question of how training progresses between and within ses- sions was also studied by Dekker, Sitskoorn, Denissen, and Van Boxtel (2014) for the alpha frequency band, and they addition- ally found specificity in training lower (8–10Hz) versus upper (10–12 Hz) sub-bands. The question whether the healthy ageing brain is also susceptible to plasticity and learning is addressed by the paper of Staufenbiel, Brouwer, Keizer, and Van Wouwe (2014), who showed that this is indeed the case for beta (12–20 Hz) and gamma (36–44 Hz) neurofeedback. At the other end of nor- mal human development, Gruzelier, Foks, Steffert, Chen, and Ros (2014a) show that alpha/theta neurofeedback has a beneficial effect on creativity in normal 11-year old school children, which extends to sustained attention. Alpha/theta neurofeedback was also found to enhance musical creativity in both novice and elite music per- formance in an extensive and well-controlled study by Gruzelier, Holmes, Hirst, Bulpin, Rahman, Van Run, and Leach (2014b).
The above-mentioned studies all employed adequate designs, state-of-the-art methods of analysis and/or they validated their findings by correlating the psychophysiological changes with learn- ing indices (see for review Gruzelier, 2013a,b,c). These rigorous strategies have been developed predominantly in university lab- oratories in which normal healthy participants were used as test subjects. It is the result of the progress in the neurofeedback field that very few studies appear nowadays in which these issues are not handled adequately. Research in the clinical field lags behind in this respect, which is understandable for a variety of reasons, such as practical and ethical ones, but which is also undesirable Arns, Heinrich, and Strehl (2014) provide an important and well-written review of how methodological issues in ADHD research have pro- gressed over time, and provide advice on how to improve on this situation. The study reported by Meisel, Servera, Garcia-Banda, Cardo, and Moreno (2014) had applied many of their recommen- dations, and they found that children with ADHD benefited to an equal extent from forty theta/beta1 neurofeedback training sessions and from medication with methylphenidate, but only neu- rofeedback contributed to academic performance. In addition, the effects lasted for a period of at least six months. In another well- controlled clinical study, Schabus, Heib, Lechinger, Griessenberger,
Klimesch, Pawlizki, Kunz, Sterman, and Hoedlmoser (2014) showed that increasing the sensorimotor rhythm (SMR,12–15 Hz) over the central cortex improves sleep quality and memory performance in insomniacs.
Taken together, and other neurofeedback empirical reports in the SAN special issues (Bergstrom, Seinfield, Arroyo-Palacious, Slater, & Sanchez-Vives (this issue); Gruzelier, 2013d; Gruzelier, Thompson, Redding, Brandt, & Steffert, 2013; Peeters, 2013), the studies reported in this special issue provide an overview of impor- tant current developments in the field of neurofeedback. It is difficult if not impossible to dispute the effects of neurofeedback training after reading through the papers in this issue. However, which specific protocols to use in which clinical or non-clinical cases, how many training sessions should be applied before effects can be seen in those cases, how long these effects last, which exact brain mechanisms are involved, etcetera, are important questions that do not have clear answers in many specific instances, but which clearly warrant further investigations. In this sense, this special issue should be viewed not only as an overview of the current state of affairs, but also as a starting point for further study into neuroplasticity.
We are grateful to Prof. Ottmar Lipp for granting us the oppor- tunity to publish this special issue in Biological Psychology and to Elsevier for encouraging SAN to undertake special journal issues to promote the field of applied neuroscience.
Available online 8 December 2013