A Review of Transcranial Magnetic Stimulation for Cognitive Impairment: Evidence for Expansion of Clinical Indications

Abstract

Background Cortical regions such as the dorsolateral prefrontal cortex (dlPFC) and its associated networks exhibit dysfunctional activity in a multitude of mental illnesses. Neuromodulation of cortical areas via non-invasive brain stimulation (NIBS) modalities such as rTMS are emerging as a promising treatment option to optimize regional and network activity in order to reverse cognitive impairment. Methods: The databases Ovid, Medline, and Embase were searched using the terms: (((((transcranial magnetic stimulation) OR transcranial direct current stimulation)) AND ((traumatic brain injuries) AND mood disorders))) OR ((((transcranial magnetic stimulation) OR transcranial direct current stimulation)) AND ((dementia) AND ((cognition disorders) OR cognit* impairment))). The filters “english language” and “humans” were applied to the initial search. We adhered to PRISMA guidelines and the results were manually sorted into randomized controlled studies by three independent reviewers. Results: 360 initial results were filtered to distill 42 randomized/sham-controlled trials. Of these, 9/21 demonstrated statistical significance of rTMS superior to sham in behavioral measures of cognition. High frequency rTMS (10 Hz) yielded positive results, though ultra-HF (20-30 Hz) also led to improvements (2/9). While L dlPFC was the most stimulated region (5/9), targeting R IFG, bilateral dlPFC, R dlPFC, and Precuneus in isolation was also beneficial. Conclusions: Findings demonstrate improvements in cognition across a variety of neuropsychiatric disorders spanning the spectrum of neurocognitive domains. TMS findings are explored to identify paradigms favoring behaviorally measurable improvements, and to harness utility of imaging technologies in combination with TMS for biomarker-related diagnostic purposes. “Negative” results offer important insights as well. Conflicts of Interest: None Funding: Personal