There is much literature to back the efficacy of this process
As an example, The American Academy of Pediatrics reached the conclusion in October 2012 that EEG Biofeedback (aka Neurofeedback) is a level 1 (Best support) Evidence-Based Practice for the Attention and Hyperactivity and other recent evidence of the efficacy of the Neurofeedback for ADHD.
A creative psychologist at the University of Chicago made a very important discovery. Dr. Joe Kamiya discovered that some of his research subjects could learn to control the amplitude and frequency characteristics of their own electroencephalogram (EEG) if provided feedback about those characteristics. Many psychologists and medical practitioners soon sensed the possibilities such operant control of the nervous system electrical activity might have for clinical treatment. Within a few years, the term biofeedback was applied to these methods and to similar procedures involving other physiological processes. One of the first successful applications of biofeedback (EEG biofeedback or neurotherapy) was in the training of the brains of children having intractable epilepsy which had not responded to medications or surgery. the first application occurred as far back as the 1950s.
Frank H Duffy, M.D., a Professor and Pediatric Neurologist at Harvard Medical School stated in an editorial in the January 2000 issue of the journal "Clinical Electroencephalography" that scholars literature now suggest that neurofeedback, "should play a major therapeutic role in many difficult areas. In my opinion, if any medication had demonstrated such a wide spectrum of efficacy it would be universally accepted and widely used: (p.v). "It is a field to be taken seriously by all" (p.vii) A large body of literature exists and is accessible on all search engines by using keywords such as: quantitative EEG, neurotherapy conditions