Effect of transcranial direct current stimulation and transcranial magnetic stimulation on the cognitive function of individuals with Alzheimer's disease: a systematic review with meta-analysis and meta-regression

ObjectiveTo analyze the effects of transcranial direct current stimulation (tDCS) and transcranial magnetic stimulation (TMS) on the cognitive function of individuals with Alzheimer's disease (AD).MethodsThis systematic review with meta-analysis and meta-regression included randomized clinical trials published until 05/2022. We included studies conducted with individuals with AD of both sexes, aged between 55 and 85 years, treated with tDCS, TMS, or both.ResultsTwenty-one studies were included in the systematic review and sixteen in the meta-analysis. Meta-regression suggested a significant influence of anodic tDCS with current intensity of 1.5 mA on cognitive function. Significant results were found with treatment frequencies of three and five days a week for two weeks. Subgroup analysis found that anodic tDCS influences cognitive function, regardless of AD stage. Similar was observed for TMS using a frequency of 20 Hz and current intensity of 90% of the resting motor threshold.DiscussionAnodal tDCS and 20 Hz TMS have demonstrated the ability to improve cognitive function in AD by modulating neural activity. These therapies are safe and well-tolerated, offering promise as adjuncts to available pharmacological treatments. Studies with greater methodological rigor and parameter standardization are warranted. Comprehensive investigations involving neuroimaging techniques may provide a better understanding of the interaction between induced electrical fields and the complex neural networks affected in AD, paving the way for more personalized and effective neurostimulation approaches