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Self-reported effectiveness of electroencephalogram-based neurofeedback (EEG-NF) against the core symptoms of attention-deficit hyperactivity disorder (ADHD) in adolescents/adults remains unclear. We searched PubMed, Embase, ClinicalKey, Cochrane CENTRAL, ScienceDirect, Web of Science, and ClinicalTrials.gov from inception to August 2021 for randomized clinical trials (RCTs) of EEG-NF with self-reported ADHD symptom ratings. Comparators included participants on waitlist/treatment as usual (TAU) or receiving other interventions. Of the 279 participants (mean age = 23.48; range: 6–60) in five eligible RCTs, 183 received EEG-NF treatment. Forest plot demonstrated no difference in inattention (SMD = −0.11, 95% CI −0.39–0.18, p = 0.46), total score (SMD = −0.08, 95% CI −0.36–0.2, p = 0.56), and hyperactivity/impulsivity (SMD = 0.01, 95% CI −0.23–0.25, p = 0.91) between EEG-NF and comparison groups. Nevertheless, compared with waitlist/TAU, EEG-NF showed better improvement in inattention (SMD = −0.48, 95% CI −0.9–−0.06, p = 0.03) but not hyperactivity/impulsivity (SMD = −0.03, 95% CI −0.45–0.38, p = 0.87). Follow-up 6–12 months demonstrated no difference in inattention (SMD = −0.01, 95% CI −0.41–0.38, p = 0.94), total score (SMD = 0.22, 95% CI −0.08–0.52, p = 0.15), and hyperactivity/impulsivity (SMD = −0.01, 95% CI −0.27–0.26, p = 0.96) between the two groups. Dropout rate also showed no difference (RR = 1.05, 95% CI 0.82–1.33, p = 0.72). Our results support EEG-NF for improving inattention in adolescents/young adults, although its effectiveness against hyperactivity/impulsivity remains inconclusive.

The significance of probability discounting (PD) among individuals with Internet gaming disorder (IGD) remains unclear. Following the PRISMA guidelines, we systematically searched the PubMed, Embase, and ScienceDirect databases for English articles on Internet addiction that included comparison between individuals with and without IGD as well as probabilistic discounting task as the main outcome from January 1970 to July 2020 using the appropriate keyword strings. The primary outcome was the overall difference in rate of PD, while the secondary outcomes included the difference in PD with magnitude of probabilistic reward and response time of the PD task. Effect size (ES) was calculated through dividing the group means (e.g., h value or AUC) by the pooled standard deviations of the two groups. A total of five studies with 300 participants (i.e., IGD group, n = 150, mean age = 20.27 ± 2.68; healthy controls, n = 150, mean age = 20.70 ± 2.81) were analyzed. The IGD group was more willing to take risks in probabilistic gains but performances on probabilistic losses were similar between the two groups. The IGD group also exhibited a shorter response time (Hedge’s g = − 0.51; 95%CI = − 0.87 to − 0.15). Meta-regression demonstrated a positive correlation between maximum reward magnitude and PD rate (p p