Non-invasive brain stimulation for cognitive impairment after traumatic brain injury: an umbrella review of systematic reviews
Background Cognitive impairment is a frequent and disabling consequence of traumatic brain injury (TBI). Non-invasive brain stimulation (NIBS), including repetitive transcranial magnetic stimulation (rTMS) and transcranial direct current stimulation (tDCS), has been investigated as a potential adjunctive intervention, but review-level conclusions remain inconsistent. Methods We conducted an umbrella review of published systematic reviews evaluating NIBS for cognitive outcomes after TBI. PubMed, Cochrane Library, Embase, Web of Science, CNKI, and Wanfang were searched from inception to May 2026. The unit of analysis was the systematic review, not individual primary trials. Eligible reviews assessed rTMS, tDCS, or both, and reported cognitive outcomes. Methodological quality was reappraised using AMSTAR-2, and primary-study overlap was assessed from the existing review-by-study citation matrix using corrected covered area (CCA). Where reviews reported quantitative estimates for cognition, these estimates were summarized descriptively at the review level; no de novo primary-study meta-analysis and no independent treatment-effect estimation were performed. The protocol was registered in PROSPERO (CRD420261395308). Results Twenty-nine records were identified. Ten review records were included, consisting of seven core evidence reviews and three supplementary reviews. Eight reviews directly addressed cognitive outcomes, while supplementary reviews provided contextual review-level evidence. Conservative AMSTAR-2 reassessment found no high- or moderate-quality reviews; two were rated low and eight critically low in the complete 10-record assessment. The citation matrix contained 42 unique primary studies and 92 primary-study occurrences across 10 review records, yielding a CCA of 13.23%, consistent with high overlap. Previously published quantitative review-level estimates showed inconsistent directions of evidence and did not demonstrate consistent evidence of an overall cognitive benefit. Conclusion Current review-level evidence does not demonstrate consistent evidence of an overall cognitive benefit of NIBS after TBI. Because available reviews are methodologically limited and clinically heterogeneous, routine use of NIBS for post-TBI cognitive rehabilitation is not supported outside research or carefully selected clinical contexts.