Photobiomodulation effects on cognitive function - a systematic review and meta-analysis of randomized controlled trials.

Photobiomodulation can alleviate the severity or delay the development of cognitive impairment through early prevention and intervention. This systematic review summarizes the effectiveness of photobiomodulation in improving cognitive function across various populations. Clinical randomized controlled trials from the establishment of the database to October 2024 were searched in PubMed, Web of Science, EMBASE, and the Cochrane Library according to PRISMA guidelines. Trials comparing the effects of PBM treatment with placebo or sham stimulation on cognitive function in healthy adults or subjects with cognitive impairment were included. Two independent researchers conducted literature screening, data extraction, and quality assessment of the included studies. Meta-analyses were performed using random effects models with Review Manager V.5.4 software. The methodological quality of the studies was evaluated using the Cochrane Risk of Bias tool. Sensitivity analyses were performed using Stata V.15.1 software. A total of 24 randomized trials involving 820 participants met the inclusion criteria. Compared with the control group, PBM treatment showed significant benefits for subjects in terms of global cognitive function (SMD = 0.66, 95% CI: 0.23 to 1.08, P = 0.003), working memory span (SMD = 1.41, 95% CI: 0.78 to 2.04, P < 0.0001), attention (SMD = -1.15, 95% CI: -2.05 to -0.24, P = 0.01) and the reaction time of executive function (SMD = -1.10, 95% CI: -1.86 to -0.33, P = 0.005) aspects. In the subgroup analyses, with the exception of no differences in both reaction time of working memory and accuracy of executive function, cognitive impaired subjects showed some improvement in other all cognitive domains (attention test only for healthy subjects), while healthy subjects showed an insignificant improvement in reaction time of executive function. This meta-analysis found that PBM treatment positively impacts global cognitive function, working memory, and executive function in persons with cognitive impairment, and partially improved global cognitive function, working memory and attention in the healthy population. However, this finding should be treated with caution due to the heterogeneity and limitations of the studies. Registration number: CRD42024552832. Registration data: 2024/06/10.