A Pilot Study Comparing Effects of Bifrontal Versus Bitemporal Transcranial Direct Current Stimulation in Mild Cognitive Impairment and Mild Alzheimer Disease

OBJECTIVE: While transcranial direct current stimulation (tDCS) can enhance aspects of memory in patients with mild cognitive impairment (MCI) and Alzheimer disease (AD), there has been wide variability in both the placement of tDCS electrodes and treatment response. This study compared the effects of bifrontal (anodal stimulation over the dorsolateral prefrontal cortices), bitemporal (anodal stimulation over the temporal cortices), and sham tDCS on cognitive performance in MCI and AD. METHODS: Seventeen patients diagnosed with MCI or mild AD received 3 sessions of anodal tDCS (bifrontal, bitemporal, 2 mA for 20 minutes; and sham) in random order. Sessions were separated by 1 week. The Alzheimer's Disease Assessment Scale–Cognitive Word Recognition Task, Alzheimer's Disease Assessment Scale–Cognitive Word Recall Task, 2-back, and Montreal Cognitive Assessment were used to assess cognition. RESULTS: There was a significant effect of stimulation condition on 2-back accuracy (F(2,28) = 5.28 P = 0.01, η(2)p = 0.27), with greater improvements following bitemporal tDCS compared with both bifrontal and sham stimulations. There were no significant changes on other outcome measures following any stimulation. Adverse effects from stimulation were mild and temporary. CONCLUSIONS: These findings demonstrate that improvements in specific memory tasks can be safely achieved after a single session of bitemporal tDCS in MCI and mild AD patients.