Parietal and Prefrontal Transcranial Magnetic Stimulation (TMS) for Mild Cognitive Impairment (MCI): A Pilot Randomized Clinical Trial

Background Even though studies of repetitive transcranial magnetic stimulation (rTMS) have demonstrated improvements in cognitive function, we know little about what site of stimulation would be ideal for improving memory. Methods We investigated two sites: (1) the dorsolateral prefrontal cortex (DLPFC); and (2) the lateral parietal cortex (LPC), a more novel site. Forty amnestic MCI participants were randomized to one of three rTMS groups: (1) active DLPFC; (2) active LPC; and (3) sham. After completing 20 sessions of MRI-neuronavigated, bilateral rTMS, the participants were followed for 6 months. The primary outcome/endpoint was the California Verbal Learning Test-II (CVLT-II) list learning score assessed at 1-week post intervention. Results Thirty-seven of 40 randomized participants provided primary endpoint data. Compared with the sham group, the active LPC group performed significantly higher on CVLT-II list learning ( p = .048; standardized mean difference (SMD) = 0.86). No significant differences in CVLT-II list learning were detected between the active DLPFC and sham groups ( p = .629; SMD = 0.20). Exploratory analyses revealed that the active LPC group performed better than sham on CVLT-II long-delay recall at the 1-week-post primary endpoint ( p = .004; SMD = 1.30), and higher on CVLT-II semantic clustering at the 3-month follow-up ( p = .015, SMD = 1.16). Conclusion The parietal cortex is a promising TMS target for improving memory function in MCI. More definitive trials are needed to compare the efficacy of parietal and DLPFC TMS for treatment of memory and cognitive impairment.