The aim of this scoping review is to systematically map methodological and analytical gaps in EEG-NFB studies, evaluate the current state of interventions in both athletes and non-athletes, and identify priorities for advancing transparency, reproducibility, and neurophysiological validity in future research.
2. Materials and Methods
2.1. Protocol and Registration This scoping review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses extension for Scoping Reviews (PRISMA-ScR [ 28 ]). The protocol was developed a priori, following PRISMA-P guidelines [ 29 ] and methodological recommendations from the Joanna Briggs Institute [ 30 ]. To ensure transparency, reproducibility, and methodological rigor, the review was prospectively registered on the Open Science Framework (OSF). The protocol defines the eligibility criteria, outlines procedures for study selection, data extraction, and synthesis, and specifies the use of Rayyan software for independent screening by two reviewers [ 31 ]. The complete protocol is publicly accessible under the DOI registration: https://doi.org/10.17605/OSF.IO/XCUWY (accessed on 22 October 2025).
2.2. Eligibility Criteria The research question was developed using the PCC framework—Population, Concept, and Context [ 30 ]. The target population included adults ≥ 18 years, divided into three groups: (i) elite athletes, training and competing at professional or international levels, with weekly physical activity typically >9 METs (vigorous-intensity [ 32 ]; (ii) amateur athletes, engaged in regular but non-professional sports practice, typically 3–9 METs; and (iii) non-athletes, healthy adults without organized sport participation, typically <3 METs. These classifications were based on the Compendium of Physical Activities [ 32 ]. The concept focused on EEG-NFB as the primary intervention. Only studies reporting objective neurophysiological or cognitive outcomes were eligible (e.g., event-related potentials (ERP), quantitative electroencephalography (qEEG), low-resolution electromagnetic tomography (LORETA); or validated measures of attention, working memory, reaction time). Studies based solely on self-reported questionnaires or satisfaction ratings were excluded. The context included sports and laboratory settings. Eligible studies could come from any country, year, or language, provided full-text access and accurate translation into English or Portuguese. Only original empirical studies were included randomized controlled trials (RCTs), quasi-experimental, cohort, observational, qualitative, or mixed-method studies with explicit NFB interventions. Exclusions comprised systematic reviews, meta-analyses, theoretical papers, editorials, and conference abstracts—although these were screened for additional references. Studies were excluded if they: (i) involved clinical populations, (ii) failed to report detailed NFB protocols or outcomes, (iii) assessed only non-specific effects (e.g., expectancy, placebo), or (iv) lacked peer-review. Full-text availability was mandatory.
2.3. Information Sources and Search Strategy The research team conducted an extensive literature search across seven academic databases: PubMed/MEDLINE, Embase, Scopus, Web of Science, PsycINFO, Cochrane Library, and LILACS. Both controlled vocabulary terms (MeSH, DeCS) and free-text terms were used to link NFB with EEG, cognitive performance, ERP, qEEG, and LORETA. Boolean operators and truncations were adapted for each database. To minimize publication bias, grey literature sources were also searched, including Google Scholar, ProQuest Dissertations & Theses, Trip Database, and Dissertations Citation Index. Reference lists of included studies were hand-searched to identify additional articles. No restrictions were applied regarding year, language, or country of origin, provided accurate translation could be ensured. References were deduplicated in EndNote X9 (Clarivate Analytics), and records were screened independently by two reviewers using Rayyan [ 31 ]. The complete database search strategies, including the detailed list of keywords applied, are reported in the Supplementary Materials (Appendix S1)
2.4. Study Selection Process The Rayyan system (Qatar Computing Research Institute) was employed to conduct the study selection process in two phases. In the first phase, two independent reviewers (RZ and TB) screened titles and abstracts against the eligibility criteria. In the second phase, the same reviewers conducted a full-text evaluation of studies that passed the initial screening. Disagreements were resolved through discussion, and when consensus could not be reached, a third reviewer (IBB) acted as arbitrator. Additionally, the reference lists of included studies were manually reviewed to identify further eligible records. The entire selection process was documented through the PRISMA-ScR flow diagram, including reasons for exclusion during the full-text stage. To enhance methodological rigor, the procedure underwent independent double verification, thereby ensuring transparency, reliability, and reproducibility.
2.5. Data Charting Process and Data Items The first reviewer (RZ) independently performed the data charting process using a structured extraction form based on the PCC framework. A second reviewer (TB) verified all extracted data, while the first reviewer (RZ) and a third reviewer (IBB) resolved any discrepancies through discussion. The extraction process included study characteristics (authors, year, country, study design), population details (type of participants: elite athletes, amateur athletes, or non-athletes; age range; gender distribution; and level of competition), characteristics of the NFB intervention (protocol type, frequency band, number and duration of sessions), neurophysiological assessment tools (ERP, qEEG, LORETA), cognitive outcome measures, and methodological aspects. In addition, although not pre-specified in the initial charting form, all studies were systematically reviewed for the use of modern spectral parameterization methods (e.g., FOOOF [ 23 ]) and for transparency and reproducibility practices (e.g., pre-registration, data sharing, code availability, detailed reporting of analysis pipelines; cf. [ 21 22 ]). These exploratory assessments were included to provide further insight into the analytical and methodological rigor of NFB research in sport. 33, The evaluation also focused on methodological strength through an assessment of sham controls (none, Active, or Inert), blinding procedures, and statistical approaches. Following [ 19 34 ], sham controls were operationally categorized as Active Sham—non-contingent but plausible feedback (e.g., pre-recorded EEG or randomized signals)—and Inert Sham, fully decoupled from participants’ physiological activity (e.g., random tones or pre-recorded videos). This classification allows for a clearer evaluation of methodological rigor, reducing the risk of conflating non-specific engagement effects with genuine NFB-related changes. A summary of the distribution of sham control types across studies is presented in the Section 3 (Figure 4) to providing a visual overview of this critical methodological factor. When any essential information was unclear or unavailable, the corresponding study authors were contacted by email. However, response rates were limited, and missing data were coded as “not reported”. Finally, the entire process was piloted on five studies to ensure consistency and clarity in the data extraction procedure, with particular emphasis on identifying the presence and type of sham controls as a critical methodological factor.